Book of Abstracts PLENARIES TALKS POSTERS Topics A Multiscale phenomena in plasticity B Residual stresses C Cyclic deformation behavior, crack initiation & crack growth of metals D In-situ microscopy and diffraction E Size effects and small-scale mechanical behavior of materials F Advanced steels and steel composite materials G Fracture mechanics H Materials for fission and fusion I High temperature materials K Polymer based composites L Lightweight alloys and structures M Ultrastrong metallic and non-metallic glasses X General mechanical behavior Karlsruhe Institute of Technology · Institut für Angewandte Materialien Engelbert-Arnold-Str. 4 · 76131 Karlsruhe · Germany phone: +49 (0) 721 608-24815 mail: info@icm12.com Contents CONTENTS 1 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Plenary Talks  The treatment of residual stresses in fracture mechanics calculations: Bob Ainsworth ..................................... 25 X-Mechanics for Metal Plasticity: W. A. Curtin ..................................................................................................... 25 Materials for ultra high-temperature applications: Haruyuki Inui, Kyosuke Kishida, Norihiko L. Okamoto ......26 Materials Innovation for Nuclear Energy - Super ODS Steels R&D: Akihiko Kimura, Wentuo Han, Hwanil Je, Yoosung Ha, Hiroyuki Noto, Dongsheng Chen, Noriyuki Iwata, Ryuta Kasada, Takanari Okuda, Shiheharu Ukai, Masayuki Inoue, Peng Dou, Sanghoon Noh ............................................................................ 27 Tensile and fatigue behavior of steels in high pressure hydrogen gas atmospheres: Hisao Matsunag, Junichiro Yam, Saburo Matsuoka ....................................................................................................................... 28 Deformation, Fatigue, and Fracture of Ultrafine Grained and Nanocrystalline Materials: A. Hohenwarter, T. Leitner, O. Renk, C. B. Yang, M. Kapp, L. Krämer, P. Gupta, V. Maier, R. Pippa ................................................. 28 Damage Tolerance in Natural and Bioinspired Structural Materials: Robert O. Ritchi ........................................ 29 Talks Topic A1: Multiscale phenomena in plasticity  Talks Topic A1 Atomistic Simulations as Bridge between Experiments and Mesoscale Models: a Case-Study on Dislocation-Precipitate Interactions in Ni-base Superalloys: Erik Bitzek .............................................................. 32 Accelerated molecular dynamics study of grain boundary motion and dislocation nucleation from grain boundary: Shigenobu Ogata, Akio Ishii, Yunjiang Wang, Junping Du....................................................... 33 Ab initio-based atomistic model simulation of deformation and fracture in SiC power device: Yoshitaka Umeno, Atsushi Kubo, Shijo Nagao .................................................................................................... 33 Research on constitutive model of nickel-based superalloy and the numerical simulation during superalloy blade cold rolling process: Xiangwei Kong, Wenran Geng, Chunlin Qiu ............................................................ 34 Development of Mechanism-Based and Microstructure-Sensitive Modeling Approach to Plastic Deformation in Multi- Phase Alloys: Duchao Lv, Pengyang Zhao, Don McAllister, Stephen Niezgoda, Michael Mills, Yunzhi Wang ................................................................................................................................ 35 Talks Topic A2 Size-Dependent Mechanical Properties of Crystalline Nanoparticles: Dan Mordehai ......................................... 37 Molecular dynamics study of the response of a nanowire containing defects to a uni-axial strain: case of nickel: Kahina Lounis, El hocine Megchiche, Zenia Hand ..................................................................... 37 Tension/compression anisotropy in yeild stress and Bauschinger effect in ultrafine-grained metals: Tomohito Tsuru, Yoshiteru Aoyagi, Yoshiyuki Kaji, Tomotsugu Shimokawa .................................................... 38 Particle and solid solution strengthening.  Part 1: experiments to control microstructure: Philipp Schu- macher, Stefan Pogatscher, Marco J Starink, Christoph Schick, Olaf Kessler, Volker Mohles, Benjamin Milkereit ............................................................................................................................................................... 39 Particle and solid solution strengthening. Part 2: modelling plastic behaviour: Volker Mohles, Volker Pankoke, Philipp Schumacher, Benjamin Milkereit ................................................................................ 40 Talks Topic A3 Comparison of statistical descriptors for the construction of Statistically Similar RVEs: Lisa Scheunemann, Daniel Balzani, Dominik Brands, Jörg Schröder ............................................................................................... 42 Phase transitions’ energies and activation energies from nothing else than indentation loading curves: Gerd Kaupp ........................................................................................................................................................... 43 2 Contents Rate effects in finite element modeling of transformation induced visco-plasticity: Maher El Haj Kacem, Fabrice Barbe, Nicolas Lecoq .............................................................................................................................. 44 Talks Topic A4 Size effects in void growth from nano- to microscale: Javier Segurado, Hyung-Jun Chang, Javier LLorca ........46 Dislocation interaction across grain boundaries and grain boundary yielding in a discrete dislocation dynamics framework: Markus Stricker, Daniel Weygand .................................................................................. 46 Dislocation alignment tensors: their conservation laws and how to determine them from discrete dislocation configurations: Thomas Hochrainer .................................................................................................. 47 Representation of Dislocation Interactions in a Dislocation Density Field Theory for Crystal Plasticity: Severin Schmitt, Peter Gumbsch, Katrin Schulz ................................................................................................ 47 Microstructural comparison of continuum models for dislocation plasticity: Mehran Monavari, Michael Zaiser, Stefan Sandfeld ......................................................................................................................... 49 Talks Topic A5 The «Cauchystat»: accurate control of the true stress in molecular dynamics simulations of martensitic phase transformations: Ronald E. Miller, Ellad B. Tadmor, Noam Bernstein, Fabio Pavia, Josh Gibson .........51 Multiscale modeling of solute atom effect on critical resolved shear stress of Fe: Masato Wakeda, Shigenobu Ogata .................................................................................................................................................. 51 Multi-scale modeling of dislocation-precipitate interactions in Fe: from molecular dynamics to discrete dislocations: A. Lehtinen, F. Granberg, L. Laurson, K. Nordlund, M. Alava ..................................................... 52 Detailed description of the screw dislocation motion in iron revealed by atomistic simulations: Ghiath Monnet, Akiyoshi Nomoto ................................................................................................................................... 53 Depinning-Controlled Plastic Deformation during Nanoindentation of BCC Iron Thin Films and Nanoparticles: Roman Kositski, Dan Mordehai ........................................................................................................................... 53 Talks Topic A6 Gradient enhanced modeling of fcc and bcc nanocrystalline materials: Benjamin Klusemann, Swantje Bargmann, Yuri Estrin ......................................................................................................................................... 56 A consistent homogenization theory for a higher order plasticity model from meso to macro scale: Phan Van Tung, Poh Leong Hien .......................................................................................................................... 57 Spectral Method Simulations of High Phase-Contrast Materials: A Joint Numerical–Experimental Study:  M. Diehl, P. Shanthraj, P. Eisenlohr, C.C. Tasan, F. Roters, D. Raabe .................................................................. 58 Influence of the microstructure of Al-components on the life time of integrated circuits: F. Meier, C. Schwarz, E. Werner ......................................................................................................................................... 59 Deformation behavior of gradient materials with nanostructured near surface regions: Florian Rieger, Andrey Molotnikov, Xiaolei L. Wu, Yuntian T. Zhu, Thomas Böhlke, Yuri Estrin ............................................. 59 Talks Topic A7 Modelling the thermomechanical behaviour of the polycrystalline microstructure of dual phase steels during sheet bulk metal forming: Stefan Loehnert, Sebastian Zeller, Peter Wriggers ...................................... 62 Computational assessment of the microstructure-dependent plasticity of lamellar gray cast iron: Mario Metzger, Thomas Seifert .......................................................................................................................... 62 A Multiscale approach for thermo-mechanical simulations of loading courses in cast iron brake discs: Christoph Herrmann, Stefan Schmid, Daniel Schneider, Michael Selzer, Britta Nestler ............................... 63 Multi-physics, Multiscale Modeling of Plastic Deformation in Plasma-Facing Components: N.M. Ghoniem, J. Blanchard, D. Rivera, E. Gao, M. Wasfy, C. Martin ......................................................................................... 64 3 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic A8 A Continuum Model for Dislocation Dynamics in Three Dimensions using the Dislocation Density Potential Functions: Yang Xiang, Yichao Zhu ...................................................................................................................... 66 A Minimalistic Continuum Approach to Formation of Dislocation Patterns Under Multislip Conditions: Dominik Steinberger, Stefan Sandfeld, Michael Zaiser ..................................................................................... 66 Orientation Dependence of the Forest Strengthening Studied with Dislocation Dynamics Simulations: Vanessa Verbeke, Stefan Sandfeld, Benoit Devincre .......................................................................................... 67 Formation of Persistent Dislocation Patterns in the Similitude Regime: Stefan Sandfeld, Michael Zaiser ......... 68 Structural model of dislocation plasticity and twinning for high-rate deformation of metals: Alexander Mayer, Vasiliy Krasnikov, Elijah Borodin ............................................................................................................ 68 Talks Topic A9 Stress and Strain Fluctuations in Plastic Deformation of Crystals with Disordered Microstructure: Olga Kapetanou, Markus Stricker, Daniel Weygand, Michael Zaiser .............................................................. 71 Strain localization and surface effects in 2D and 3D stochastic models of amorphous plasticity: David Fernandez Castellanos, Stefan Sandfeld ................................................................................................. 72 Numerical investigataion of welding residual stress field in tubular joints considering the effects of solid-state phase transformation: Kimiya Hemmesi, Majid Farajian, Dieter Siegele ............................................ 72 The influence of GP and GDP precipitates on the viscoplastic material behaviour of Inconel 718: Andreas Drexler, Hermann Maderbache, Hans-Peter Gänser, Werner Ecker , Andreas Fischersworring- Bunk, Bernd Oberwinkler ................................................................................................................................... 73 A representative volume element based multiscale modeling of fish scale: A.M. Rajendran, M.P. Nelms ......... 74 Multiscale crystal plasticity simulation on anisotropic yielding behavior of ultrafine-grained metal: Yoshiteru Aoyagi .................................................................................................................................................. 75 Topic B: Residual stresses  Talks Topic B1 Fatigue Strength of Anodized Al 7050-T7451. Herman Jacobus Cornelis Voorwald, José André Marin de Camargo, Maria Odila Hilário Cioffi, Midori Yoshikawa Pitanga Costa ..................................................... 77 The Influence of Residual Stress on the Failure Modes in a Thermal Barrier Coating System: Dong Liu, Claudia Rinaldi, Peter E J Flewitt ........................................................................................................................ 78 Overloads on cracks: using Barkhausen microscope and SEM-based digital image correlation to evaluate mechanisms and effects on local (residual) stress fields: Matthias Thielen, Meisam Sheikh-Amiri, Michael Marx, Christian Boller, Christian Motz .............................................................................................. 78 Assessment of shot-peening on fatigue life prediction: microstructural effects. Louise Toualbi, Pascale Kanouté, Serge Kruch, Arnaud Longuet, Alexandre Seror, Jean-Patrick Goulmy, Quentin Puydt ................ 79 Thermal Stability of Residual Stresses in Ti-6Al-4V components. Aleksandar Stanojevic, Hermann Maderbacher, Paul Angerer, Bernd Oberwinkler ............................................................................................. 80 Development of residual stresses during cyclic loading in the very high cycle fatigue regime: Hongwang Fu, Benjamin Dönges, Hans-Jürgen Christ ............................................................................................................... 81 Talks Topic B 2 3DXRD microscopy applied to study stress-induced martensitic transformation over one hundred individual grains in a shape-memory alloy polycrystal: Sophie Berveiller, Benoit Malard, Younes El-Hachi, Jonathan Wright ................................................................................................................................................. 83 Measuring Residual Stresses in Monolithic Fuel Foils using Neutron Diffraction: Bjørn Clausen, Donald W. Brown, Maria A. Okuniewski, Levente Balogh, Thomas A. Sisneros .............................................. 83 4 Contents Characterization of microscopic stress and strain evolved in polycrystalline Fe-Ga alloys using synchrotron radiation: Shigeru Suzuki, Yusuke Onuki, Shigeo Sato, Shun Fujieda, Kozo Shinoda, Kentaro Kajiwara, Masugu Sato ........................................................................................................................................................ 84 Analysis and Assessment of Residual Stresses in Ground Steels and Ceramics: A. Liehr, W. Zinn, B. Scholtes ...85 Assessing material properties with Neutron and Synchrotron radiation - Two complementary tools: T. Buslaps, V. Honkimäki, M. DIMICHIEL, J. WRIGHT, A. FITCH, C. Curfs, T. Pirling ............................................................... 85 Talks Topic B 3 Estimation of residual stress distribution in polyethylene pipes. Jan Poduška, Pavel Hutař, Jiří Sadílek, Jaroslav Kučera, Martin Ševčík, Luboš Náhlík ................................................................................................... 88 A combined experimental and numerical approach to the investigation of the influence of geometry on residual stresses in structural glass: Mithila Achintha, Bogdan Balan ............................................................... 89 Benefits of Whole Powder Pattern Decomposition in the Determination of Residual Stress in Multiphase Materials: Hugues Guérault, Jens Brechbuehl.................................................................................................... 90 Simulation-based optimization of the multiple incremental hole-drilling method for the simultaneous ana- lysis of residual stresses and the measurement accuracy: Frank Schweizer, Melanie Senn, Wulf Pfeiffer ......90 Analysis of residual stress gradients by X-ray diffraction with five-axis diffractometer: Alex Ulyanenkov, Andrei Benediktovitch, Tatiana Ulyanenkova, Josef Keckes ............................................................................... 91 Comparsion of the residual stress distributions in conventional and stationary shoulder friction stir welding: Tianzhu Sun, Yingchun Chen, Philip B. Prangnell, Matthew J. Roy, Philip J. Withers ...................................... 92 Talks Topic B 4 Nitriding stress due to nitrogen diffusion and nitride formation: Tatsuo Inoue ................................................... 94 Infuence of rotational speed in friction stir welding on heat generating behavior of MPS analysis: Hisashi Serizawa, Taku Hayami, Fumikazu Miyasaka ........................................................................................................ 94 Failure analysis and optimization of welding process for 347H boiler tube of thermal power plant: Han-sang Lee, Jine-sung Jung, Doo-soo Kim, Keun-bong Yoo ............................................................................................ 95 Evaluation of the interfacial shear stress between FeCrAl coating and Zircaloy-4 fuel cladding: Yang Liu, Imran Bhamji, Philip J. Withers, Weicheng Zhong, Peter Mouche, Brent J. Heuser, Michael Preuss ............ 96 Mechanical property and Residual Stress in Type304 stainless steel repaired partially by HVOF sprayed technique: Masayuki Arai, Sho Tanaka, Tatsuo Suidzu ....................................................................................... 97 Comparative residual stress measurements on shot peened spring steel by XRD and PRISM hole drilling method: Theo Rickert, Dominik Dapprich, Carlo Scheer .................................................................................... 98 Talks Topic B 5 Combined machining/burnishing process optimization for alloy steel 42CrMo4 using Taguchi technique: Anis Rami, Salem Sghaier, Hedi Hamdi, Samir Lahouar .................................................................................... 100 The residual stress homogeneity state induced by gear manufacturing processes: Fritz Klocke, Jefferson Gomes, Christoph Löpenhaus, Ronnie Rego ..................................................................................................... 100 Influence of specimen size on the residual stress formation after heat treatment of hot-work tool steel components: M. Schemmel, P. Prevedel, R. Schöngrundner, W. Ecker, T. Antretter ..................................... 101 Effect of different surface treatments on A7N01S-T5 aluminum alloy butt joints fatigue properties: Chuanping Ma, Hui Chen, Qimeng Zhu,Yuanming Ma, Xu Zhao ....................................................................... 102 Thermomechanical behaviour and microstructural evolution of high temperature forged Ti-6Al-4V during heat treatment quenching: Renaud Julien, Vincent Velay, Vanessa Vidal, Mehdi Salem, Yoann Dahan, Romain Forestier, Farhad Rezaï-Aria ................................................................................................... 102 Development of ProCast® Models to Predict Residual Stress within Femoral Implant Castings: Brian Conroy, Alan Kavanagh, David Tanner ................................................................................................... 103 5 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic B 6 Evolution of residual stresses and work hardening during cycling loading and their impact on fatigue behavior of a single crystal nickel based superalloy: Amélie Morançais, Pascale Kanouté, Manuel François, Mathieu Fèvre, Anaïs Gaubert .......................................................................................................... 106 Numerical and Experimental Description of the Surface and Subsurface Residual Stresses in Metallic Components after Mechanical Surface Treatment : Majid Farajian, Mirko Boin, Robert C. Wimpory, Michael Hofmann, Alexandru D. Stoica, Ke An ................................................................................................ 107 Evaluation of stress determination methods for a 2D x-ray diffraction portable apparatus using in-situ measurements during tensile testing: Joaquin Ramirez Rico, Jinjing li, Seung Yub Lee, Ismail Cevdet Noyan .................................................................................................................................................................. 108 Laboratory Micro-focus X-ray Sources for Stress Measurements: Bernd Hasse, Andreas Kleine, Jörg Wiesmann, Carsten Michaelsen ........................................................................................................................ 109 Phase-Field Model for Solid-Solid Phase Transformation Driven by Elasticity. Oleg Tschukin, Daniel Schneider, Britta Nestler ................................................................................................................................. 109 Talks Topic B 7 Experimental and Numerical Investigation of Residual Stress Relaxation in Shot-Peened Notch Geometries under Low-Cycle Fatigue: Chao You, Mithila Achintha, Katherine Soady, Philippa Reed ................................. 111 Analysis of compositionally ungraded FGM analogues: Neutron diffraction measurements of residual stress and mechanical testing of pressure sintered Mo-Y2O3 and Mo-Al2O3 systems: Michael Saleh, Dorji Chavara, Karl Toppler, James Alexander, Andrew Ruys, Kaveh Kabir, Vladimir Luzin ...................... 112 The distribution laws of residual stress of high speed trains by statisatical method: Guoqing Gou, Hui Chen, Yuping Yang, Jia Chen ............................................................................................................................... 113 How to depict measured data and results in the matrix method: balder Ortner ............................................. 113 Finite Element modeling and investigation of the process parameters in Deep Rolling of a plane geometry: Nataliya Lyubenova, Dirk Baehre ...................................................................................................................... 114 Topic C: Cyclic deformation behavior, crack initiation & crack growth of metals   Talks Topic C 1 Effect of chemical heterogeneity on the low-cycle-fatigue behavior of austenitic Cr–Ni stainless steels: Jiří Man, Marek Smaga, Ivo Kuběna, Alice Chlupová, Jaroslav Polák............................................................. 117 The distribution of local plastic deformation during VHCF loading of duplex stainless steel and martensitic steel: Alexander Giertler, Rudolf Denk, Ulrich Krupp .................................................................................... 118 Fatigue mechanisms of an austenitic-ferritic duplex stainless steel at loading conditions close to the conventional fatigue limit: Benjamin Dönges, Claus-Peter Fritzen, Hans-Jürgen Christ ................................ 118 Material Development for Precision Steel Tubes for Stabilizer Bars: Mario Mücher, Robert Brandt .............. 119 Effect of Cementite Morphology on Fatigue Crack Propagation in Smooth Steel Specimen: Zhou-Jia Xi, Motomichi Koyama, Yuichi Yoshida, Nobuyuki Yoshimura, Kohsaku Ushioda, Hiroshi Noguchi .................. 120 Talks Topic C 2 The role of corrosion pit in corrosion fatigue crack initiation process of 12Cr stainless steel: Ryuichiro Ebara .................................................................................................................................................. 122 Characterization of the fatigue behavior of the metastable austenitic steel X6CrNiNb1810 from LCF to VHCF at 300°C: Andreas Sorich, Marek Smaga, Dietmar Eifler, Tilmann Beck ............................................... 122 Influence of the surface morphology on the cyclic deformation behaviour of cryogenic turned metastable austenitic steel X6CrNiNb1810: Robert Skorupski, Marek Smaga, Dietmar Eifler, Tilmann Beck .................. 123 Hybrid surface treatment on austenitic stainless steel JIS SUS316 to improve fretting fatigue strength: Toshihiro Omori, Tatsuro Morita, Kohei Okada, Hideaki Maeda ..................................................................... 124 6 Contents Low cycle fatigue behaviors of hot-bent 347 Stainless Steels in a simulated PWR water: Junho Lee, Jong-Dae Hong, Changheui Jang ....................................................................................................................... 125 Effect of Cold-Drawing on High-Cycle Fatigue Properties of Austenitic TWIP and Fully Pearlitic Steels: Seok Weon Song, Jeong Hun Lee, Hyong Jik Lee, Chul Min Bae, Chong Soo Lee ............................................. 126 Talks Topic C 3 Influence of characteristics of inclusion on rolling contact fatigue of bearing steel: Eiichi Tamura, Yusuke Sandaiji, Takehiro Tsuchida ............................................................................................................................... 128 Evaluation of the fatigue behavior of damage tolerant TRIP-modified SAE 52100 steels using the short- time-procedures PHYBALCHT- and PHYBALLIT: Marcus Klein, Hendrik S. Kramer, Tilmann Beck, Dietmar Eifler ................................................................................................................................................................... 129 The development of the indirect method for estimation of strain life fatigue parameters: Robert Basan, Domagoj Rubeša, Marina Franulović .............................................................................................................. 130 Fatigue Properties of DLC Coated Steel AISI1045 with Cr Diffusion Layer on the Substrate Surface by AIH-FPP Process: Kenta Ueyama, Koji Kobayashi, Hiroyuki Akebono, Jun Komotori, Atsushi Sugeta .............131 Low cycle fatigue properties of the Fe-28Mn-5Cr-6Si-0.5NbC alloy: Nobuo Nagashima, Takahiro Sawauchi, Kazuyuki Ogawa ................................................................................................................................................. 132 Talks Topic C 4 Effects of nitriding temperature on the fatigue properties of Ti-6Al-4V alloy and in-situ observation of fatigue cracks in 4-points bending: Shoichi Kikuchi, Sho Yoshida, Yuta Nakamura, Akira Ueno, Yoshikazu Nakai ................................................................................................................................................................... 134 The influences of foreign object damage on the high cycle fatigue behavior of titanium alloy TC11: Zhao Zhenhua, Chen Wei, Wu Tieying ............................................................................................................... 135 Effect of forging condition on fatigue behavior in AZ61 bulk nanostructured metal fabricated by multi- directional forging: Yoshihiko Uematsu, Toshifumi Kakiuchi, Taishi Nozaki, Hiromi Miura ............................ 135 Variable-Amplitude of Aluminum Alloy 7075 in the VHCF Regime under Superimposed Loading Conditions: S.E. Stanzl-Tschegg, M. Meischel, N. Iyyer, A. Arcari, N. Phan ........................................................................ 136 Talk Topic C 5 Assessment of fatigue crack closure under in-phase, out-of-phase and phase-shift thermomechanical fatigue loading using a temperature dependent strip yield model: Carl fischer, Christoph schweizer, Thomas seifert.................................................................................................................................................... 138 Dwell time effects on the Thermo-Mechanical Fatigue Behaviour of a Wrought Ni-base Alloy: Stefan Guth, Jonas Müller, Karl-Heinz Lang ......................................................................................................................... 139 Biaxial fatigue behavior of a hot-pressed metastable austenitic steel: Stephanie Ackermann, Tim Lippmann, Sebastian Henkel, Horst Biermann .................................................................................................. 140 High temperature low cycle fatigue behavior of cast superalloy Inconel 713LC coated with ZrO2-SiO2-Al2O3 nanocrystalline thermal barrier coating: Karel Obrtlik, Ladislav Čelko, Tomáš Chráska, Ivo Šulák, Lenka Klakurková, David Jech, Viktor Škorík, Jiří Švejcar ............................................................................... 141 Optimal Design of Skirt Supporting Structure of Coke Drum for Thermal-Mechanical Cyclic Loading: Edward Wang, Zihui Xia .................................................................................................................................... 142 Numerical and experimental analysis of the influence of process parameters on the damage of hot rolling rolls: Luiz Gustavo Del Bianchi da Silva Lima, Alexandre Gonçalves, Ana Paola Villalva Braga, Izabel Fernanda Machado, Roberto Martins de Souza, Mário Boccalini Jr. ............................................................ 143 Talks Topic C 6 Rolling Contact Fatigue Strength of Ceramic Coated Steel Laser-Quenched after Coating Process: Hirotaka Tanabe, Yuki Nakamura, Yui Izumi, Tohru Takamatsu ....................................................................... 145 7 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Crack propagation behavior in titanium alloy under combined axial-torsional cyclic loading modes: Toshihiko Hoshide, Tetsuya Tokuhara, Masashi Nagaoka ............................................................................... 145 The AA2124/SiC metal matrix composites under fatigue, creep and monotonic loading conditions: Agnieszka Rutecka, Paweł Grzywna, Lech Dietrich ......................................................................................... 146 Fatigue crack growth behavior of Ti-6Al-4V ELI alloy under constant amplitude loading with different single overloads: Chuanyong Chen, Duyi Ye, Xumin Hu, Jianzhong Liu, Lina Zhang ........................................ 147 Prestrain memory on subsequent cyclic behavior of FCC metallic materials presenting different dislocation slip tendencies: Gael Marnier, Clement Keller, Lakdhar Taleb ..................................................... 148 Talks Topic C 7 The effects of periodic overloads and high/low loading blocks on fatigue crack growth of aluminum alloy: Haifeng Xu, Duyi Ye, Lei Xiao, Jianzhong Liu, Lina Zhang .................................................................................. 150 Multiaxial fatigue damage in fibrous composites: an approach based on micromechanical crack growth: Roberto Brighenti, Andrea Carpinteri, Daniela Scorza .................................................................................. 150 Predicting the fatigue life at crack initiation in cruciform welded joints by using the effective cyclic J-integral (∆Jeff): Desire Tchoffo Ngoula, Heinz Thomas Beier, Michael Vormwald ....................................... 151 Fatigue behavior of Al/Steel dissimilar resistance spot welds fabricated using Al-Mg insert film: Ren Ito, Ishak Ibrahim, Yoshihiko Uematsu, Toshifumi Kakiuchi, Yun Kyyoul, Chihiro Matsuda ................... 152 High cycle fatigue strength of pure lead: Masahiro Endo, Keiko Morita, Akira Yasunaga ............................... 153 Talks Topic C 8 Accuracy improvement of fatigue damage evaluation based on phase analysis of dissipated energy: Daiki Shiozawa, Tsuyoshi Inagawa, Atsushi Akai†, Takahide sakagami ............................................................ 155 Fatigue damage evaluation of polycrystaline alloy by diffraction contrast tomography using ultra-bright synchrotron radiation: Yoshikazu Nakai, Daiki Shiozawa, Shoichi Kikuchi, Shota Matsuda, Ryota Nakao ......156 Dislocation-based modelling of low cycle fatigue in FCC single and polycrystals: Nicolò Grilli, Koenraad G. F. Janssens, Helena van Swygenhoven ......................................................................................................... 156 3D dislocation dynamics simulation of crack shielding and blunting in FCC metals: Laurent Korzeczek, Benoit Devincre, Riccardo Gatti, Arjen Roos ................................................................................................... 157 Analysis of the cyclic plastic response of materials based on the hysteresis loop shape: Roman Petráš, Jiří Tobiáš, Jaroslav Polák ................................................................................................................................. 158 Talks Topic C 9 The role of graphite in fatigue crack growth of ductile cast iron under the presence of internal and external hydrogen: Takashi Matsuo, Kosei Yamada, Hisao Matsunaga, Masahiro Endo, Saburo Matsuoka ............... 160 Shear mode crack propagation along with plastic flow of small area Shuto Fukudome, Sigeru Hamada, Masaharu Ueda, Hiroshi Noguchi ........................................................... 161 A Continuum Damage Mechanics Approach For Prediction of Fatigue Crack Initiation Life: Shiva Kumar Chitta, m.m.mayuram .................................................................................................................. 161 Generalized critical fatigue crack length for transition from microstructure-driven to mechanics-driven propagation: Yasuaki Hamano, Motomichi Koyama, Kaneaki Tsuzaki, Hiroshi Noguchi ................................. 162 Fatigue crack growth characteristic under hydrogen atmosphere in an ultra-low frequency region in Low Carbon and Interstitial Free Steels: Yousuke Onishi, Motomichi Koyama, Atsushi NIshimoto, Daisuke Sasaki, Yasuji Oda, Hiroshi Noguchi .................................................................................................................. 162 Short crack growth kinetics in heat resistant austenitic stainless steel Sanicro 25: Veronika Mazánová, Jaroslav Polák, Guocai Chai .............................................................................................................................. 163 8 Contents Talks Topic C 10 Application of area parameter for estimation of thereshold stress intensity factor range ∆Kτth of small shear-mode cracks Saburo Okazaki, Hisao Matsunaga, Masahiro Endo ......................................................... 166 Fatigue crack initiation near inclusions in Ni superalloys – a SEM based study with high resolution EBSD: Jun Jiang, Jie Yang, Tiantian Zhang, Maki Kuwabara, Fionn Dunne, Ben Britton .......................................... 167 Non-destructive evaluation of multiple-site small cracks in high-temperature low cycle fatigue of an austenitic stainless steel by using multipoint probe DC potential difference measuring system: Shio Nakanishi, Takayuki Suzuki, Yuji Nakasone ............................................................................................... 167 Crack detection by Sonic-IR method using ultrasonic wave inputted through water: Yui Izumi, Hirotaka Tanabe, Tohru Takmatsu1, Takahide Sakagami .................................................................................................. 168 Low-cycle fatigue Simulation in micro-scale to obtain fatigue behavior of bimodal AL alloys: H. Hosseini- Toudeshky, M. Jamalian ..................................................................................................................................... 169 Fatigue of automotive engine cylinder heads – A new model based on crack propagation and micro- structure interaction: Guillaume Morin, Romain Dejean, Jean-Michel Fiard, Mathieu Beranger .................. 169 Topic D: In-situ microscopy and diffraction  Talks topic D 1 In-situ TEM deformation of lightweight alloys and local strain measurements with diffraction imaging: Andrew M. Minor .............................................................................................................................................. 172 CSL Σ3 and Σ9 activity as a deformation pathway in nanocrystalline Pd and AuPd: Aaron Kobler, Christian Kübel1, Horst Hahn ........................................................................................................................... 172 In-situ characterization of martensite plasticity by high resolution microstructure and strain mapping: C.C. Tasan, L. Morsdorf, M-M. Wang, D. Barbier, O. Jeannin, D. Raabe ........................................................... 173 Complex analyses of mechanical and electrical performance of metallic thin films on flexible substrates combined with in-situ Reflectance Anisotropy Spectroscopy: Andreas Wyss, Matthias Schamel, Richard Denk, Michael Hohage, Alla S. Sologubenko, Ralph Spolenak ....................................................................... 174 Crystallographic and mechanical charactization of micro-bicrystal cantilevers: S. Zaefferer, N. Bozzolo, S. Kleindiek, A. J. Smith ....................................................................................................................................... 174 Talks Topic D 2 In-situ micro-mechanical testing at the sychrotron: Steven Van Petgem ........................................................... 176 Optimizing Single Crystal Growth for Detector Applications using Energy-dispersive Neutron Imaging: H. Matthias Reiche, Sven C. Vogel, Edith D. Bourret, Adrian Losko, Anton Tremsin, Gregory A. Bizarri, Martin M. Gascon, Didier Perrodin, Eric C. Samulon ..................................................................................... 176 Time-resolved (4D) in situ x-ray tomographic microscopy at TOMCAT: Understanding the dynamics of materials: J.L.Fife, F. Marone, R. Mokso, M. Stampanoni .................................................................................. 177 Grain and subgrain high resolution diffraction from polycrystalline bulk materials: Ulrich Lienert, Wolfgang Pantleon, Gábor Ribárik, Tamás Ungár .......................................................................................... 178 Advanced Laboratory X-ray Microscopy : In Situ Materials Characterization and Diffraction Contrast Tomography: Arno Merkle, Christian Holzner, Benjamin Hornberger, Hrishikesh Bale, William Harris, Leah Lavery ........................................................................................................................................................ 179 Topic E: Size effects and small-scale mechanical behavior of materials Talks Topic E 1 Size dependent strength and its exploitation for length-scale engineered material systems: Andy Bushby, David Dunstan .................................................................................................................................................... 181 9 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Three-dimensional modeling of size effects in micromechanical testing: Edgar Husser, Erica Lilleodden, Swantje Bargmann ............................................................................................................................................. 182 Dislocation grain boundary interaction in bi-crystalline micro pillars studied by in situ SEM and in situ µLaue diffraction. Nataliya Malyar, Christoph Kirchlechner, Gerhard Dehm ................................................. 182 Size effects and dislocation structure under torsion loading of single crystalline wires: a discrete dislocation dynamics study: Daniel Weygand, Peter Gumbsch ........................................................................................... 183 Investigation of crystal plasticity of single crystal copper by using micro scale torsion test: Kozo Koiwa, Chuantong Chen, Nobuyuki Shishido, Masaki Omiya, Shoji Kamiya, Hisashi Sato, Masahiro Nishida, Takashi Suzuki, Tomoji Nakamura, Toshiaki Suzuki, Takeshi Nokuo ................................................................ 184 Talk Topic E 2 Study of fatigue damage evolution in micron sized bending beams by in situ µLaue diffraction: C. Kirchlechner, P.J. Imrich, J.-S. Micha, O. Ulrich, C. Motz ............................................................................ 186 A comparative study of fatigue properties of nanoscale Cu films on a flexible substrate: Bin Zhang, Ying Zhang, Xiao-Fei Zhu, Xue-Mei Luo, Guang-Ping Zhang ..................................................................................... 187 Strain-dependent fatigue damage of nanocrystalline 930-nm-thick Au films: Xue-mei Luo, Guang-ping Zhang .................................................................................................................................................................. 188 Influence of surface energy and dislocation pile-up on the size dependent strength of single-crystalline micro-pillars Bo Pan, Yoji Shibutani .................................................................................................................... 189 In situ fracture tests of brittle materials at the microscale: Giorgio Sernicola, Tommaso Giovannini, Rui Hao, T. Ben Britton, Finn Giuliani ............................................................................................................... 190 Talks Topic E 3 Smaller is not always stronger – inverse scale effect on metal- ceramics interface strength observed in LSI interconnect structures : hoji Kamiya, Nobuyuki Shishido, Kozo Koiwa, Masaki Omiya, Hisashi Sato, Masahiro Nishida, Takashi Suzuki, Tomoji Nakamura, Toshiaki Suzuki, Takeshi Nokuo ................................. 192 Characterisation and Mechanical Properties of the Boundary Layers of Soft Magnetic Composites: Tabea Schwark, Ruth Schwaiger, Oliver Kraft ................................................................................................. 193 Multiscale Modelling of Damage and Failure in a Biological Hierarchical Material: Ingo Scheider, Songyun Ma, Ezgi Yilmaz, Swantje Bargman ................................................................................................................... 193 Surface properties of biopolymer films - Morphology, adhesion and friction: Maurice Brogly, Ahmad Fahs, Sophie Bistac ....................................................................................................................................................... 194 Microstructure evolution of Cu/Au and Cu/Cr multilayers under cyclic sliding: Zhao-Ping Luo, Guang-Ping Zhang, Ruth Schwaiger ................................................................................................................. 195 Toward the modulation of interface barrier strength of Cu/Au nanolayered composites: Xi Li, Guang-Ping Zhang ............................................................................................................................................. 196 Talks Topic E 4 Probing thermally activated properties on a local scale: Daniel Kiener, Alexander Leitner, Verena Maier .....198 Micro- and Macro-mechanical Testing of Grain Boundary Sliding (GBS): Junnan Jiang, Angus Wilkinson, Ricahrd Todd ..................................................................................................................................................... 198 Nanoindentation at Room and Elevated Temperatures of Au/Cu-Multilayers: Thomas Kreuter, Guang-Ping Zhang, Oliver Kraft, Ruth Schwaiger .......................................................................................... 199 Mechanical behavior of the MAX-phase Nb2AlC at the nanometer and micrometer scale by means of in situ indentation: Nadine Schrenker, Yonnes Kabiri, Mirza Mačković, Julian Müller, Peter Schweizer, Florian Niekiel, Björn Hoffmann, Silke Christiansen, Erdmann Spiecker ...................................................... 200 Deformation behavior of copper thin films indented with patterned nanoindenter tips: Anke Schachtsiek, Oliver Kraft, Ruth Schwaiger ........................................................................................................................... 201 10 Contents Talks Topic E 5 Using high temperature micromechanical testing to inform microstructure based models: application to IN718: J. Molina-Aldareguia, B. Gan, A. Cruzado, M. Jiménez, J. Segurado, J. Llorca ................................... 203 Multi-scale Fracture Behaviour of Tungsten Alloys for Nuclear Fusion: Bo-Shiuan Li, David Armstrong, James Marrow, Steve Roberts ........................................................................................................................... 203 Effect of composition and morphology on the mechanical and electrical behavior of Cu-Cr thin films: Alla. S. Sologubenko, Wilhelm Hüttenes, Huan Ma, Ralph Spolenak ............................................................. 204 Thermomechanical influence grinding of electrodeposited chrome coated on a 300M substrate: Benjamin Weiss, André Lefebvre, Olivier Sinot, Albert Tidu........................................................................... 205 Orthogonal machining of a Cu-1.8wt%Be-0.1wt%Co alloy: influence of the microstructure: Alban De Saever, Albert Tidu ....................................................................................................................................... 206 Talks Topic E 6 Grain size gradient-induced work hardening and extraordinary ductilization: Xiaolei Wu, Yuntian Zhu ..........208 Mechanical properties and microstructural changes of high strength AA7075 alloy during low temperature ECAP: Sebastian Fritsch, Mario Scholze, Martin F.-X. Wagner ....................................................................... 208 Effect of creep and aging on the precipitation kinetics of an Al-Cu-Alloy after ECAP: Markus Härtel, Kevin G. Abstoss, Swetlana Wagner, Philipp Frint, Peter Mayr, Martin F.-X. Wagner ................................... 209 On shear localization in an SPD-processed Aluminum Alloy – Part 1: Microstructures and local mechanical properties: Philipp Frint, Steffen Pfeiffer, Martin F.-X. Wagner ..................................................................... 209 On shear localization in an SPD-processed Aluminum Alloy– Part 2: A simple model concept and FE simulation of the formation of alternating bands: Steffen Pfeiffer, Philipp Frint, Martin F.-X. Wagner .......210 Talks Topic E 7 Bio-inspired, self-assembled functionalized Fe3O4 nanoparticles with tunable machanical properties: Gerold A. Schneider, Axel Dreyer, Artur Feld, Ezgi Yilmaz, Andreas Kornowski, Tobias Krekeler, Heshmat Noei, Martin Ritter, Andreas Stierle, Hosrt Weller ....................................................................................... 212 In situ SEM compression tests of layered crystals : Peter Schweizer, Florian Niekiel, Erdmann Spiecker ......212 Material development for high-strength nanocomposites: Almut Schroer, Jens Bauer, Oliver Kraft ............ 213 Mechanical behavior of ultrathin aluminum oxide films: Influence of open or closed porosity: A. van der Rest, F. Henry, A. Favache, J. Proost, Q. Van Overmeere, T. Pardoen .............................................. 214 Influences of vacancy defects on compressive behaviors of open-tip carbon nanocones: Ming-Liang Liao .....215 TalksTopic E 8 Size Effect of Single Crystalline Noble FCC Metal Nanowires: In-Suk Choi.......................................................... 217 Mechanical Behavior of Fivefold Twinned Nanowires understood from Anisotropic Elasticity: Florian Niekiel, Erdmann Spiecker, Erik Bitzek .............................................................................................................. 217 Mechanical properties of nano-twinned Ag wires: Aaron Kobler, Thorsten Beuth, Tobias Klöffel, Markus Moosmann, Horst Hahn, Christian Kübel, Bernd Meyer, Erik Bitzek, Thomas Schimmel ................ 218 Influence of artificial defects on the mechanical behavior of Au nanowires: Charlotte Ensslen, Christian Brandl, Gunther Richter, Oliver Kraft ............................................................................................ 219 In-Situ Electromechanical Properties of ZnO Nanowires: Sanjit Bhowmick, Ude Hangen, Douglas Stauffer, Syed Asif .............................................................................................................................................................. 219 11 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Topic F: Advanced steels and steel composite materials Talks Topic F 1 Mechanical Properties of a 0.2%C–1.5%Si–5%Mn TRIP-aided Annealed Martensitic Steels: Kohichi Sugimoto, Hikaru Tanino ................................................................................................................................... 221 Nano-laminate TRIP-TWIP steel with dynamic strain partitioning and enhanced damage resistance: C. C. Tasan, M-M. Wang, D. Ponge, D. Raabe ..................................................................................................... 221 Characterization of strain localizations during plastic deformation of TRIP/TWIP steels: Anja Weidner, Christian Segel, Horst Biermann ...................................................................................................................... 222 Temperature evolution during tensile straining of high Mn twinning induced plasticity (TWIP) steels: JeeHyun Kang, Tobias Ingendahl, Wolfgang Bleck .......................................................................................... 222 Microstructure as well as mechanical and magnetic properties of Fe-based alloys with different contents of metastable austenite: Marek Smaga, Dietmar Eifler, Tilmann Beck ............................................................ 223 Microstructural Evolution of TRIP-aided Medium Mn Steel During Warm Deformation: Yongmoon Lee, Chong Soo Lee .................................................................................................................................................... 224 Talks Topic F 2 Influence of temperature on fatigue-induced martensitic phase transformation in a metastable CrMnNi-steel: Horst Biermann, Matthias Droste, Alexander Glage ............................................................... 226 Importance of ε-martensite on embrittlement and fatigue crack growth in Fe-Mn-based austenitic steels: Motomichi Koyama, Huichao Li, Takahiro Sawaguchi, Kaneaki Tsuzaki, Hiroshi Noguchi ............................. 226 Importance of strain aging on fatigue limit in austenitic TWIP steels: Yuusuke Yamamura, Motomichi Koyama, Renqing Che, Takahiro Sawaguchi, Kaneaki Tsuzaki, Hiroshi Noguchi............................................. 227 Influence of Si addition on deformation and fracture behaviors of aging treated cast Fe-Mn-Al-C lightweight steel: Soon Il Kwon, Je Hyun Lee, Seong Jun Park, Hyun Uk Hong ................................................ 228 Effect of shot peening on microstructure of steels exhibiting a TRIP effect – Experimental and modeling approaches: Romain Guiheux, Sophie Berveiller, Denis Bouscaud, Régis Kubler, Etienne Patoor, Quentin Puydt .................................................................................................................................................... 229 Study of Lüders band propagation using IR thermography and DIC method in the wide range of strain rates: Michal Maj ......................................................................................................................................................... 230 Talks Topic F 3 Homogenization of TRIP steel behaviour using a strain gradient plasticity model: M.K. Hatami, T. Pardoen, P. Berke, P.J. Jacques, T.J. Massart .................................................................................................. 232 A crystal plasticity model for advanced high strength steels including both TRIP and TWIP effect: Franz Roters, Su Leen Wong ............................................................................................................................. 232 Multiscale Modelling of Damage and Fracture in High Mn TWIP Steels: Manjunatha Madivala, Christian Segel, Anja Weidner, Horst Biermann, Wolfgang Bleck, Ulrich Prahl ........................................ 233 Artificial microstructure model and its applications on plasticity and damage of the dual phase steels: Napat Vajragupta, Mohamed Sharaf, Junhe Lian, Sebastian Münstermann, Wolfgang Bleck ..................... 234 Dislocation plasticity in precipitate hardened advanced austenitic lightweight high-Mn steels by coupled TEM and DDD simulations: Strengthening and dislocation-based mechanisms: E. Welsch, S.M. Hafez Haghighat, I. Gutierrez-Urrutia, D. Raabe ........................................................................................................ 235 Phase-field modeling of solid-solid phase transformations: Daniel Schneider, Oleg Tschukin, Michael Selzer, Britta Nestler ......................................................................................................................................... 236 12 Contents Talks Topic F 4 Z phase strengthened steels for ultra-supercritical power plants: Daniel F. Urban, Christian Elsässer, Hermann Riedel .................................................................................................................................................. 238 Different mechanical behavior of MA957 ODS and Eurofer’97 steels exposed to flowing helium of 720˚C: Anna Hojna, Hynek Hadraba, Jana Kalivodova, Roman Husak ........................................................................ 238 Characterization of the weldability of different AHS steel and aluminium alloy grades using thermo- mechanical physical simulation: János Lukács, László Kuzsella, Zsuzsanna Koncsik, Ádám Dobossy, Dóra Pósalaky .................................................................................................................................................... 239 The microstructure characterization of the HAZ and welding CCT diagram of API X100 steel: Chunlin Qiu, Liangyun Lan, Xiangwei Kong ............................................................................................................................ 240 Weldability of modern high strength bainitic steel: Liangyun Lan, Xiangwei Kong, Chunlin Qiu .................... 241 Topic G 1: Fracture mechanics Talks Topic G 1 Numerical Simulation of ZrO2(Y2O3) Ceramic Plate Penetration by Cylindrical Plunger: Vladimir Bratov, Nikita Kazairnov, Yuri Petrov ............................................................................................................................ 243 Temporal Peculiarities of Fracture Caused by Threshold Pulses in Spallation: Grigory Volkov, Yuri Petrov, Yuri Mescheryakov, Natalia Mihaylova ................................................................................................ 243 Dynamic fracture of concrete: Experimental and numerical studies on compact tension and L- specimen: Joško Ožbolt, Uwe Mayer, Natalija Bede, Akanshu Sharma .............................................................................. 244 Multiscale model of the dynamic tensile fracture of solid and molten metals: molecular dynamics and continuum mechanics: Alexander Mayer, Vasiliy Krasnikov, Polina Mayer .................................................... 245 Stage I fatigue crack studies in order to validate the dislocation-free zone model of fracture for bulk materials: Florian Schäfer, Michael Marx, Horst Vehoff ............................................................................... 246 Talks Topic G 2 The Mechanics of Bridged Fatigue Cracks: Jamie J. Kruzic .................................................................................. 248 On the need to reconsider fatigue crack growth at negative stress ratios: Christoper Benz, Manuela Sander ................................................................................................................................................................. 248 Effect of adjacent small defects on fatigue limit of steels: Mari Åman, Saburo Okazaki, Hisao Matsunaga, Gary Marquis ................................................................................................................................ 249 Comparison between three fatigue damage models and experimental results for composite materials submitted to spectrum loading: Mohammed Bousfia, M. Aboussaleh, B. Ouhbi, R.Boukhili .......................... 250 Experimental and numerical analysis of damage in random fibrous networks: E. Sozumert, E. Demirci, M. Acar, B. Pourdeyhimi, V. V. Silberschmidt.................................................................................................... 251 Talks Topic G 3 A boundary finite element for anisotropic/piezoelectric materials containing multiple cracks: Chyanbin Hwu, Shao-tzu Huang ........................................................................................................................................ 253 Effect of micromorphology on crack growth in cortical bone tissue: X-FEM study: Mayao Wang, Xing Gao, Adel Abdel-Wahab, Simin Li, Elizabeth A. Zimmermann, Christoph Riedel, Björn Busse, Vadim V. Silberschmidt ..................................................................................................................................................... 254 Extended damage modelling for fracture control in modern line pipe steels: Aida Nonn ................................. 254 Talks Topic G 4 Cleavage Initiation Angle for High Strength Steels under Mixed-Mode Conditions: Zefeng Zhang, Xudong Qian ....................................................................................................................................................... 257 13 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Experimental and numerical investigations on the crack growth stage of crane runway girders subjected to cyclic loading: Philipp Rettenmeier, Eberhard Roos, Stefan Weihe, Xaver Schuler ........................................ 258 Crack Path in connection with the Two-Parameter Fracture Mechanics Approach on X52 steel pipe repairing: M. Hadj Meliani, G. Pluvinage, Y.G. Matvienko ................................................................................ 259 A modified Sih criterion for crack deflection in dipolar gradient elasticity: Ioannis D. Gavardinas, Antonios E. Giannakopoulos ............................................................................................................................. 259 Cohesive laws for adhesive layers loaded in a state close to pure shear: Ulf Stigh, Anders Biel ...................... 260 The role of Geometrically Necessary Dislocations in the fracture process of metallic materials: Emilio Martínez-Pañeda, Christian Niordson .................................................................................................. 261 Talk Topic G 5 On the fracture toughness of bulk-metallic glasses: Bernd Gludovatz, Jamie J. Kruzic, Marios D. Demetriou, William L. Johnson, Robert O. Ritchie........................................................................................... 263 Damage & Fracture Toughness of Fibrous Dual-Phase Steels for Automotive Applications: Karim Ismail, Thomas Pardoen, Pascal J. Jacques, Laurence Brassart, Astrid Perlade ........................................................ 263 New insights on the physically correct application of the J-integral for characterizing fatigue crack growth in elastic–plastic materials: Walter Ochensberger, Otmar Kolednik ............................................................... 264 Grain Boundary Precipitation and Creep Crack Growth in polycrystalline Ni-base superalloys: H. Sommer, C. Somsen, F. Mueller, V. Knezevic, N. de Boer, J. Klöwer, G. Eggeler ............................................................. 265 Examination of Evaluation Method for Static Strength of Casting Materials by Regarding Shrinkage Porosity as Cracks: Example of AZX912 Mg Cast Alloy: Yu-ki Higuchi, Naoya Ochi, Hiroshi Noguchi ............. 265 Insight into MAG welding under constructive constraint conditions by means of high energy synchrotron X-ray diffraction: Florian Vollert, Jens Gibmeier, Jonny Dixneit, Thorben Fischer, P.Staron, Arne Kromm, Thomas Kannengiesser ........................................................................................................................ 266 Talks Topic G 6 Testing fracture toughness of britle materials via chevron- notched bend bars of microscopic length-scale: Goran Zagar, Martin Mueller, Vaclav Pejchal, Lionel Michelet, Marco Cantoni, Andreas Mortensen ....268 Micro-fracture testing of tungsten single crystals: Christoph Bohnert, Nicola Schmitt, Sabine M. Weygand, Ruth Schwaiger, Oliver Kraft ......................................................................................................... 268 An Improved Micromechanical Method for Investigating the Statistical Strength of Poly-Silicon Membranes: John Brückner, Holger Pfaff , Alfons Dehé, Sven Rzepka ............................................................................. 269 How Crystals Break – Crack speed dependent environmental effect and surface instabilities Anna Gleizer, Liron Ben-Bashat Bergman, Dov Sherman ................................................................................ 270 Talks Topic G 7 Influences of hydrogen-affected yielding and work hardening on plastic zone evolution studied by Finite Element Method: Daisuke Sasaki, Motomichi Koyama, Kenji Higashida, Kaneaki Tsuzaki, Hiroshi Noguchi .272 On the fracture toughness of fcc medium- and high-entropy alloys at ambient to cryogenic temperatures:  Bernd Gludovatz, Keli V. S. Thurston, Anton Hohenwarter, Dhiraj Catoor, Hao Bei, Easo P. George, Robert O. Ritchie ................................................................................................................................................ 273 Stress corrosion cracking in sensitized austenitic stainless steel type 304 under tetrathionate solution environment: Tomoyuki Fujii, Keiichiro Tohgo, Yutaro Miura, Yoshinobu Shimamura ................................. 273 Effect of post weld heat treatment on the long-term reliability of austenitic stainless steel 347H: Jine-sung Jung, Han-sang Lee, Doo-soo Kim, Keun-bong Yoo ......................................................................... 274 Interaction between torsion damage and toughness anisotropy in a drawn pearlitic steel wire: Aurélie Jamoneau, Jean-Hubert Schmitt, Denis Solas ...................................................................................... 275 14 Contents Topic H 1: Materials for fission and fusion Talks Topic H 1 Effects of helium and irradiation damage on microstructure and mechanical properties of Fe base alloys for fusion applications: Richard Kurtz ............................................................................................................... 277 New Material Developments for Applications in Fusion Reactors: J.W. Coenen, J. Engels, S. Heuer, A. Houben, B. Jasper1, A. Litnovsky, Th. Weber, T. Wegener, W. Biel, T. Hoeschen, F. Koch, R. Neu, J. Riesch, M. Rasinski, B. Unterberg, Ch. Linsmeier .......................................................................................... 277 Functional graded tungsten/EUROFER coating systems for First Wall application: D. D. Qu, W.W. Basuki, J. Gibmeier, R. Vassen, J. Aktaa ........................................................................................................................... 279 CuCrZr alloys reinforced by Tungsten as structural Divertor applications for DEMO: Jan Hoffmann, Steffen Antusch, Jens Reiser, Michael Rieth, Verena Widak, Soeren Mueller, Hohe Joerg ......................... 279 Lithium evaporation and redeposition experiments under high density linear plasma dumping: X. Cao, W. Ou, Z. Cao, Y. Xia, W. Zhang, X. Xue, C. Wang, J. Wang, D. Yang, S. Chen, F. Gou ......................................... 280 Talks Topic H 2 Analyzing the ions radiation-induced defects and cavity swelling evolution in representative PWR internal austenitic steels: Bertrand Michaut, Joël Malaplate, Alexandra Renault Laborne, Faiza Sefta, Daniel Brimbal, Lionel Fournier, Brigitte Décamps ......................................................................................... 282 Insights in microstructure of austenitic ods steels: Tim Graening, Michael Rieth, Anton Moeslang .............. 282 Studies of high dpa ion beam irradiation effects on fcc AA-6061 and fcc-bcc duplex steel 2205: micromechanical modelling and nano-indentation examination of hardness variations: Michael Saleh, Paul Munroe, Lyndon Edwards ......................................................................................................................... 283 Mechanical Behavior of Unalloyed Plutonium: Adam Farrow, Tarik Saleh, Deniece Korzekwa, Jeremy Mitchell .............................................................................................................................................................. 284 Temperature dependent X-ray adsorption spectroscopy studies of Fe, Cr, and Ni local atomic structure for ferritic and austenitic ODS steels: Andris Anspoks, Juris Purāns, Aleksejs Kuzmins, Pavel Vladimirov, Tim Gräning, Jan Hoffmann, Kārlis Lazdiņš1, Arturs Cintiņš, Anton Möslang, Michael Rieth .................. 284 Talks Topic H 3 Mechancial Properties of a PM2000 ODS alloy tested at temperatures up to 700°C: Ude D. Hangen, Asta Richter ........................................................................................................................................................ 287 High temperature investigation of the fusion relevant material EUROFER by instrumented indentation: Julian Bredl, Manuel Dany, Hans-Christian Schneider, Oliver Kraft ............................................................. 287 Study of irradiation creep based on nanomechanical lab-on-chip testing: Pierre Lapouge, Fabien Onimus, Yves Bréchet, Thomas Pardoen, Jean-Pierre raskin, Renaud Vayrette ........................................................... 288 Atom probe tomography of nanoscale precipitates in 13% Cr ODS steels with Ti variation: S. Rogozhkin, N. Orlov, A. Aleev, A. Bogachev, A. Nikitin, A. Zaluzhnyi, R. Lindau, A. Möslang, P. Vladimirov .................. 289 Identification of Cr-Y-O Nano-Cluster in a 14Cr Oxide Dispersion Strengthened Steel: Xue Hu, Wei Yan , Wei Wang, Yiyin Shan, Ke Yang .......................................................................................................................... 290 Deuterium retention in reduced-activation ODS steels irradiated with 20 MeV W ions : O.V. Ogorodnikova, K. Sugiyama, Z. Zhou, Yu. Gasparyan, V. Efimov ................................................................................................ 290 Talks Topic H 4 Combined effect of radiation damage and helium on the hardening and embrittlement of ferritic / martensitic steels: Yong Dai, Kun Wang, Christiane Vieh, Vladimir Krsjak ..................................................... 293 Mechanical Properties of Irradiated Ferritic/Martensitic Steels: Tarik A. Saleh, Stuart A. Maloy, Tobias Romero, Matthew E. Quintana ......................................................................................................................... 293 15 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Influence of neutron irradiation on precipitate microstructure in EUROFER97: Christian Dethloff, Ermile Gaganidze, Jarir Aktaa ........................................................................................................................... 294 Atomic scale investigation of phase decomposition of Fe-22%Cr during thermal aging and subsequent heavy ion irradiation: O. Korcuganova, A. Aleev, S. Rogozhkin ........................................................................ 295 Comparison of mechanical properties between the HT9 and Gr.92 steel with various heat treatment conditions in a viewpoint of microstructure: SangGyu Park, HyeongMin Heo, JunHwan Kim, SungHo Kim ...295 Creep rupture behavior of the China Low Activation Martensitic steel at 600°C: Xue Hu, Lixin Huang, Wei Yan, Wei Wang, Yiyin Shan, Ke Yang ............................................................................................................ 296 Talks Topic H 5 Positron annihilation research on ferrtic/martensitic steels irradiated under mixed spectrum of high energy protons and spallation neutrons: Vladimir Krsjak, Yong Dai ................................................................. 298 Loss of strength and embrittlement of neutron irradiated beryllium: V. Chakin, A. Moeslang ......................... 298 Modeling Hydrogen Ad- and Desorption on Beryllium-(0001)-Surface: Christopher Stihl, Dmitry Bachurin, Pavel Vladimirov ................................................................................................................................................ 299 Dislocation microstructure evolution in tungsten due to indentation loading simulated by discrete dislocation dynamics: Kinshuk Srivastava, Daniel Weygand, Peter Gumbsch .................................................. 300 Characterization and modelling of the mechanical behaviour of Nb3Sn: Gilles Lenoir, Veronique Aubin .......300 Characterisation and modelling of nuclear graphite : from micrometres to metres: Dong Liu, Peter Heard, Gillian Smith, Branko Savij2 Erick Schelangen, Peter Flewitt ...................................................................... 301 Talks Topic I 1 Development of a novel microstructure highly resistant to grain boundary damage during creep at 950°C in Alloy 617: Ji-Won Lee, Hyun-Hwa Park,Tae-Ho Lee, Hyun-Uk Hong .............................................................. 303 Numerical multi-criterion optimization method for developing Ni-based superalloys: Development of a software tool and experimental validation: Ralf Rettig, NilsS C. Ritter, Alexander Müller, Harald E. Helmer, Robert F. Singer ................................................................................................................................... 304 On the importance of the matrix for the creep properties of single crystal nickel based superalloys: R. Völkl, E. Fleischmann, E. Affeldt, U. Glatzel ................................................................................................ 304 Influence of misfit stresses on dislocation glide in single crystal superalloys: A three-dimensional discrete dislocation dynamics study: Siwen Gao, Marc Fivel, Anxin Ma, Alexander Hartmaier ................................... 305 TEM analysis of localized, planar deformation events which govern creep of single crystalline CoNi-super alloys with γ/γ´-microstructures: Yolita M. Eggeler, Julian Müller, Michael S. Titus, Akane Suzuki, Tresa M. Pollock, Erdmann Spiecker ............................................................................................................... 305 Talks Topic I 2 On the Formation of Ledges and Grooves at γ/γ′ Interfaces of Single Crystal Superalloys: Alireza B. Parsa, Philip Wollgramm, Hinrich Buck, Aleksander Kostka, Christoph Somsen, Antonin Dlouhy, Gunther ggeler ................................................................................................................................................................. 308 The influence of Re and Ru on the high-temperature creep strength and phase stability of Ni-based superalloys: Kamil Matuszewski, Ralf Rettig, Robert F. Singer........................................................................ 308 Super-Solvus Heat Treatments of Ni-Based Superalloys in a Hot Isostatic Press/Quench Unit: Lais Mujica Roncery, Inmaculada Lopez-Galilea, Benjamin Ruttert, Werner Theisen ....................................................... 309 Crystal plasticity modeling of porosity reduction in an as-cast Ni-base single crystal superalloy during hot isostatic pressing: Siwen Gao, Inmaculada Lopez-Galilea, Anxin Ma, Stephan Huth, Werner Theisen, Alexander Hartmaier ......................................................................................................................................... 310 Characterization of <100> superdislocations and the γ/γ’ interface by an advanced FIB lamella lift out technique: Julian Müller, Michael J. Mills, Erdmann Spiecker ...................................................................... 311 New Experimental Results on Atomistic and Microstructural Aspects of Creep of Ni-Base Single Crystal Superalloys (SXs): H. Buck, A. Kostka, P. Nörtershäuser, A.B. Parsa, P. Wollgramm, G. Eggeler ................... 311 16 Contents Talks Topic I 3 Mechanical properties and microstructures of new polycrystalline γ/γ’ Co-base superalloys: Steffen Neumeier, Lisa Freund1, Mathias Göken ............................................................................................. 314 Investigation of the quaternary system Co-Al-W-Ta in the range of Co9Al10W2Ta: Alexander Epishin, Thomas Link, Jan Midtlyng, Nikolay Petrushin, Gert Nolze ............................................................................ 314 Influence of rhenium on the local mechanical properties of the γ and γ′ phase in cobalt-base superalloys: M. Kolb, C. Zenk, S. Neumeier, M. Göken ........................................................................................................... 315 Radiation stability of ZrSiN system under the Xe ions irradiation: Vladimir Uglov, Vitali Shymanski, Gregory Abadias, Gennagy Remnev2, Andrey Suvalov .................................................................................... 316 Effect of casting defects on high cycle fatigue behavior of nickel-based superalloy MAR-M 247: Miroslav Šmíd, Stanislava Fintová, Ludvík Kunz, Pavel Hutař, Karel Hrbáček ............................................... 317 Finite Element Simulation of the creep behavior of directionally solidified NiAl-9Mo: Jürgen Albiez, Ioannis Sprenger, Martin Heilmaier, Thomas Böhlke .................................................................................... 317 Talks Topic I 4 On the nucleation of Mo-rich Laves phase particles in 12% Cr tempered martensite ferritic steels:   Aleksander Kostka, Mehmet Ikbal Isik, Gunther Eggeler ............................................................................... 320 Temperature dependent solid solution strengthening of Nickel by transition metal solutes: Hamad ur Rehman, Karsten Durst, Steffen Neumeier, Roger Reed, Mathias Göken ....................................................... 320 Effect of the Stress Multi-Axiality on the Creep Damage in Fine Grained HAZ of Mod. 9Cr-1Mo Steels: Kimiaki Yoshida, Masataka Yatomi, Masaaki Tabuchi, Ken-ichi Kobayashi ........................................................ 321 Thermal stability of ferritic and austenitic nanocluster containing ODS steels: Sascha Seils, Daniel Schliephake, Daniel Janda, Alexander Kauffmann, Julia N. Wagner, Martin Heilmaier ............................... 321 Microstructure and micromechanics of directionally solidified eutectic alloys: Amritesh Kumar, Ruth Schwaiger, Oliver Kraft ........................................................................................................................... 322 Talks Topic I 5 Tungsten (W) laminate pipes made of ultrafine-grained (UFG) W foil: Jens Reiser, Simon Bonk, Jan Hoffmann, Michael Rieth ............................................................................................................................ 325 Internal Friction and Shear Modulus Temperature Dependence of 9%Cr Ferritic Steel P92 in 25 ÷750°C Temperature Range: Elguja Kutelia, George Darsavelidze, Tengiz Kukava, Temur Dzigrashvili, Ia Kurashvili, Francisco J. Perez Trujillo ........................................................................................................... 325 Bayesian approach to determine optimum inspection intervals for struct ural components of high temperature materials subjected to creep: Kyoko Nakamura, Yuji Nakasone ................................................... 326 Microstuctural study on the intermetallic compound NiAl-Cr: Antje Krueger, Michael Klimenkov, Anton Moeslang ................................................................................................................................................ 327 The crystallographic template effect preceding the formation of stable α-Al2O3 during low temperature oxidation of Fe-Al alloys: Pedro Brito, Haroldo Pinto, Anke Kaysser-Pyzalla ................................................. 327 Topic K 1: Polymer based composites   Talks Topic K 1 Integrative simulation of short glass fibers reinforced polyamides: methodology followed to identify polymer matrix constitutive models on a wide range of solicitations, temperature, moisture and strain rate: Gilles Robert, Olivier Moulinjeune ................................................................................................................... 330 X-ray microtomography and finite element modelling of the failure mechanism in epoxy syntactic foams under compressive loads: Peifeng Li, Ruoxuan Huang ........................................................................... 331 17 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Mechanical Properties of CFRTP Made from CF/PA Composite Yarn Sutured with PA Fiber: Yuji Takubo, Hiroaki Kimura, Takashi Matsuoka, Tomoko Hirayama1 Hiroyuki Fujita, Yasuji Miyata, Kunio Fujii .............. 331 Overall mehanical properties of composites with complex orientationally distributed microstructures: Olesya I. Zhupanska, Pavlo Krokhmal ................................................................................................................ 332 Estimataion of Dispersion Condition for PP/CNT Nano Composite by Using the New Segments with Extensional Flow for Co-Rotating Twin Scew Extruder: Koki Matsumoto, Takayuki Morita, Yoshihiko Arao, Tatsuya Tanaka .................................................................................................................................................... 333 Characterisation of graphene-reinforced nanocomposites: optical-microscopy analysis of spatial non- uniformity: Osman Bayrak, Mariana Ionita, Emrah Demirci, Vadim V. Silberschmidt ..................................... 334 Talks Topic K 2 Progressive damage evaluation of Glass-Epoxy laminated composites under fatigue loading: Soran Hassanifard, Mohsen Feyzi ................................................................................................................................ 336 Experimental Investigation of Cold Forming of PC-Films and tensile bars using Optical Measurements: Kai-Uwe Widany, Christian Dammann, Rolf Mahnken ..................................................................................... 337 Failure processes of fiber reinforced composites under off-axis loading: Christian Marotzke, Titus Feldmann ............................................................................................................................................................ 337 Analysis and Simulation of the Fatigue Behaviour of CFRP Laminates: Janko Kreikemeier, Lukas Geiger .........338 Inline metrology of carbon fiber preforms as an indicator of mechanical properties of consolidated CFRP parts: Daniel Brabandt, Gisela Lanza ................................................................................................................. 339 Characterization of complexly warped components made from locally reinforced UD-tape laminates: Benjamin Hangs, Tobias Link, Frank Henning .................................................................................................... 340 Talks Topic K 3 RVE modeling of fibre-reinforced-polymer curing coupled to visco-elasticity: Christian Dammann, Rolf Mahnken .................................................................................................................................................... 342 Characterization and simulation of the time-dependent anisotropic deformation behaviour of continuously reinforced PA6 material: Andreas Roesner, Luise Kaerger, Frank Henning ..................................................... 342 Topological Interlocking Materials - Towards New Polymeric Hybrid Materials: Lee Djumas, Andrey Molotnikov, George P.Simon, Yuri Estrin ......................................................................................................... 343 Homogenisation of thermoelastic properties of short-fibre reinforced polymers and validation based on experimental characterisation: L. Kehrer, V. Müller, B. Brylka, T. Böhlke ................................................... 344 Phenomenological characterization and macromechnical modeling of anisotropic, non-linear behavior of sheet molding compounds (SMC): Marina Mrkonjić, Ute Rayling, Kay André Weidenmann, Luise Kärger, Frank Henning .................................................................................................................................... 345 Topic L 1: Lightweight alloys and structures   Talks Topic L 1 Mechanical properties and microstructure of Ti6Al4V fabricated by selective laser melting: Radomila Konecna, Gianni nicoletto, Adrian Baca, Ludvik kunz ..................................................................................... 347 Formation of Twin Bands and Inhomogeneous Deformation in Mg-wrought Alloy AZ31 During Tension-Compression or Bending Loading: K. Anten, A. Liehr, B. Scholtes ....................................................... 348 Electrochemical-based characterization of the corrosion fatigue behavior of creep-resistant magnesium alloy DieMag422: Martin Klein, Philipp Wittke, Frank Walther ...................................................................... 348 Very High Cycle Fatigue (VHCF) Assessment of Selective Laser Melted (SLMed) AlSi12 Alloy: Shafaqat Siddique, Frank Walther Formability Enhancement of 7075 Al Sheet with Two Step Forming: Yong-Nam Kwon, Young Seon Lee .........349 18 Contents Talks Topic L 2 Effect of Missing Cells on the Initial Stiffness and Plastic Yielding Surface of Three-Dimensional Micro-Lattice Structures: Kuniharu Ushijima1 Dai-Heng Chen, Wesley James Cantwell .................................. 351 High-strength microarchitected cellular materials: The interplay of design and size-dependent strengthening: Jens Bauer, Oliver Kraft .................................................................................................................................... 351 Self-assembled ultra high strength, ultra stiff mechanical metamaterials based on inverse opals: Gerold A. Schneider, Jefferson J. do Rosário, Erica T. Lilleodden, Martin Waleczek, Roman Kubrin, Alexander Yu. Petrov, Pavel N. Dyachenko, Julian E.C. Sabisch, Kornelius Nielsch, Norbert Huber, Manfred Eich ............352 An efficient analysis model for the stresses in arbitrary adhesive lap joints with flat laminated adherends: Nicolas Stein, Philipp Weissgraeber, Wilfried Becker ..................................................................................... 352 Optimization of fatigue behaviour of metallic shear joints: Taha Benhaddou, Alain Daidie, Pierre Stephan, Clement Chirol, Jean-Baptiste tuery. ................................................................................................. 353 Microstructure evolution and deformation texture during rolling of TIMETAL407. Gaurav Singh, J. Quinta Da FonsecaCA, M. Thomas, M. Preuss ............................................................................................... 354 Topic X 1: General mechanical behavior  Talks Topic X 1 Wedge indentation studies of Zr-Cu-based bulk metallic glass: V. Nekouie, A. Roy, V.V. Silberschmidt ............356 Mechanics Behavior of Protein Material: Inchul Baek, Myeongsang Lee, Hyun Joon Chang, Jae In Kim, Sungsoo Na ........................................................................................................................................................ 356 Rigidity characterization and fracture analysis of the solar-grade multi-crystalline silicon plates at low temperature: Lv Zhao, Anne Maynadier, Daniel Nelias ..................................................................................... 357 Quantum field theory approach in mechanics of polycrystalline materials: Vyacheslav Shavshukov, Anatoly Tashkinov .......................................................................................................................................................... 358 Axial Crash and Crush Response of Novel Nested Tubes: Zana Eren, Fatiḣ Usta, Zafer Kazanci , Haliṫ S. Tkmen, Zahiṫ MectoĞLu ...................................................................................................................................... 359 Neutron diffraction and imaging for industrial and engineering applications: Anna Paradowska .................... 359 Talks Topic X 2 Preparation and Characterization of Neat and Thermally- treated Silicon Carbide Fibers-reinforced Gypsum Cements: Y. E. Greish, H. F. El Maghraby, O. Gedeon, O. Alnuaimi, M. S. Katsiotis, K. Polychronopoulou ....361 Phase-field modeling for microstrucurure formation of metal foam materials: Takuya Uehara ........................ 362 Fiber-reinforced Calcium Sulfate Bone Cement Composites with Enhanced Bioactivity, Mechanical Properties and Controlled Biodegradability: Yaser E. Greish1 Abdel hamid I. Mourad, Nuha F. Attia ............. 362 Mixed Elastic Variational Formulation of Composite Plates Based on Dimension Reduction Method: Mohammad Javad Khoshgoftar, Mohammad Mirzaali ................................................................................... 363 Effect of Friction on Material Mechanical Behaviour in Non-equal Channel Multi Angular Extrusion (NECMAE): Mohamed S. El-Asfoury, Mohamed N. A. Nasr, Ahmed Abdel-Moneim .......................................................... 364 Poster   Poster Topic A: Multiscale phenomena in plasticity   The effect of hydrogen on the macroscopic strain localization of steels: Svetlana Barannikova, Anatoly Malinovsky, Dmitrii Pestsov .............................................................................................................................. 367 Atomistic analyses of nucleation and propagation behavior of ridge shaped kink band in long-period- stacking-ordered phase: Ryosuke Matsumoto, Masayuki Uranagase ............................................................... 368 19 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Microtension behavior of hydrogen-containing metastable austenitic stainless steel: Ryo Matsuoka, Kaoru Koga, Yoji Mine, Kazuki Takashima .................................................................................................................... 368 Microtension behaviour of dual-phase steel subjected to pre-straining: Shinya Ogata, Yoji Mine, Kazuki Takashima, Hiroshi Shuto, Tatsuo Yokoi .......................................................................................................... 369 Adaptive boost molecular dynamics method for study of rare events in plastic deformation: Naomchi Tsuji, Akio Ishii, Junping Du, Shigenobu Ogata .......................................................................................................... 370 Quantitative evaluation of dislocation nucleation as thermal activation process via atomistic simulations: Masayuki Uranagase, Ryosuke Matsumoto ...................................................................................................... 371 Poster Topic B: Mechanical behavior   Residual stress evaluation of shot peened Ag-based contact materials via diffraction technique: Seung-Yub Lee, Jingjing Ling, Hyo-Soo Lee, Min-Ha Lee ...................................................................................................... 373 Structural phase states and residual stresses in the Ta/TiNi surface layers before and after high-current pulsed electron beam impact. L.L.Meisner, M.G.Ostapenko, M.A.Zakharova, E.Yu.Gudimova ........................ 373 The effect of residual stresses on the change of the B2 phase lattice parameter in the NiTi with Tantalum coating after pulsed electron-beam treatment: M.G. Ostapenko, L.L. Meisner, M.A. Zakharova, E.Yu. Gudimova ............................................................................................................................................................ 374 Laser assisted residual stress determination in ceramic coatings: Peter Weidmann, Giancarlo Pedrini, Venancio Martínez-García, Ulrich Weber, Andreas Killinger, Martin Wenzelburger, Siegfried Schmauder, Rainer Gadow, Wolfgang Osten .................................................................................................. 375 Poster Topic C: Cyclic deformation behavior, crack initiation & crack growth of metals   Fatigue crack initiation from notches and mean stress effect in 2024 T351 Al-alloy: Mustapha Benachour, Nadjia Benachour, Mohamed Benguediab ....................................................................................................... 377 Resonant acoustic for nondestructive inspection of accumulated damage assessment in austenitic stainless steel subjected to fatigue tests in rotating bending: Ricardo A. Casali, Maria A. Caravaca, Cesar G. Veroli, Gabriel Vallejos, Jorge Forte ............................................................................................................................ 377 Determination of the Crictical Resolved Shear Stress in a NiAl-Cr composite by Discrete Dislocation Dynamics: Herve Gakam, Daniel Weygand ........................................................................................................ 378 Cyclic softening in the MA956 ODS steel:Ivo Kubena,Jaroslav Polák, Tomáš Kruml ....................................... 378 Influence of pre-strain on fatigue crack growth behavior in rolled AZ31 magnesium alloy: Ryoichi Momoe, Shigeki Morita, Tsuyoshi Mayama, Nobusuke Hattori ...................................................................... 379 Anisotropy of cyclic deforrmation and fatigue properties in rolled AZ31 magnesium alloy: Shigeki Morita, Ryota Ikeda, Tsuyoshi Mayama, Nobusuke Hattori ........................................................................................... 380 Fatigue properties of fine-grained AZ31 magnesium alloy: Yuji Okamoto, Takahito Hori,Shigeki Morita, Hidetoshi Somekawa, Tsuyoshi Mayama, Nobusuke Hattori............................................................................ 381 Dwell effects on low cycle fatigue behaviour of diffusion coated nickel base superalloy IN 713LC at temperature of 800°C: Ivo Šulák, Karel Obrtlík, Simona Hutařová, Martin Juliš, Tomáš Podrábský, Ladislav čeklko ................................................................................................................................................... 382 Poster Topic D: In-situ microscopy and diffraction   Strain induced martensitic Transformation in Austempered Ductile Iron (ADI): Xiaohu Li, Patrick Saal, Michael Hofmann , Markus Hölzel................................................................................................................... 384 An in situ experimental method for evaluating the tensile property of single crystalline gold nanorod: Yabin Yan, Xiaoyuan Wang, Takashi Sumigawa, Takuya Nakano, Takayuki Kitamura ....................................... 384 Poster Topic E: Size effects and small-scale mechanical behavior of materials Indentation Size Effect of Nanoporous Gold: Correlated by Unique Structure and its Size-Dependent Mechanical Behavior: Seung-min Ahn, young-Cheon Kim, and Ju-Young Kim .................................................. 387 20 Contents High temperature nanoindentation - Dynamic measurements for thin film analysis: Dennis Bedorf, Martin Knieps, Wolfgang Stein......................................................................................................................... 387 Ductility in cold-rolled ultrafine-grained (UFG) tungsten (W): Correlation between microstructure and mechanical properties: Simon Bonk, Jens Reiser, Jan Hoffmann, Michael Rieth ............................................ 388 Fabrication of Al-Cu Composite Reinforced with BN by Powder Liquid-Phase Forging: Cunguang Chen, Leichen Guo, Wenwen Wang, Ji Luo, Zhimeng Guo .......................................................................................... 389 Mechanical response of nanoporous gold made from Au-Ag precursor alloys with different initial microstructure: Eun-Ji Gwak, Young-Cheon Kim, Ju-Young Kim ....................................................................... 389 Simulation of mechanical properties of nanotwin-strengthened metals: H. Hosseini-Toudeshky, M. Yadollahpour ................................................................................................................................................ 390 Nanotubular ZnO for flexible gas sensor: Na-Ri Kang, Ju-Young Kim ................................................................. 391 Improved elasticity of bilayer graphene cantilevers with interlayer shear and in-plane extension effects: Abed Moheb Shah Din, Amin Farrokhabadi ...................................................................................................... 391 Fracture of brittle spheres in compression: testing microscopic fused quartz: Vaclav Pejchal, Goran Žagar, Denis Lang, Marta Fornabaio, Andreas Mortensen ........................................................................................ 392 How to optimize the fatigue properties of bimodal microstructures of nanocrystalline (nc) and ultrafine grained (ufg) Nickel?: Dominic Rathmann, Michael Marx, Christian Motz ..................................................... 393 Surface oxidation of metallic glass surfaces and its effect on nanotribology: K. Rittgen, A. Caron, R. Bennewitz ....................................................................................................................................................... 393 Investigation of mechanical anisotropy in Mg using Berkovich indentation. Julian E. C. Sabisch, Erica T. Lilleodden ........................................................................................................................................................... 394 Size- and phase-dependent mechanical properties of ultra- thin silicon and Ge2Sb2Te5 films: Franziska Schlich, Ralph Spolenak ..................................................................................................................................... 395 Compression-shear behavior of a strongly textured Magnesium alloy AZ31 under different strain rates: Sebastian Seipp, Shibayan Roy, Benjamin Zillmann, Martin F.-X. Wagner ........................................................ 395 Roughness behaviour of nanomaterials: Sayah Tahar, Bouti Samir .................................................................. 396 Electronic properties and mechanical stability of ZnO in the bulk and nanowire structures under large uniaxial stresses: Lucy A. Valdez, Ricardo A.Casali ............................................................................................ 397 First-principles study on ferroelectricity and its coupling behavior with mechanical deformation of ultrathin PbTiO3 nanotube: Xiaoyuan Wang, Takahiro Shimada, Takayuki Kitamura ...................................................... 398 Thickness-dependent tensile properties of PEDOT:PSS: O Bae Woo, Ju-Young Kim .......................................... 398 Poster Topic F: Advanced steels and steel composite materials   Effect of filler metal on micro-structural, mechanical and corrosion behavior of austenitic stainless steel weldment 316L: A. Sriba, K. M. Rehouma, S.E. Amara, N. Madaoui ......................................................... 400 Poster Topic G: Fracture mechanics   Estimation of Fracture Toughness of Metallic Materials Using Instrumented Indentation Test: Jun-Yeong Kim, Woojoo Kim, Seung-Hun Choi, Dongil Kwon ......................................................................... 402 The experimental study of stress-strain states in stress concentrators with the use of the method of digital image correlation: Elena M. Spaskova, Evgeniy V. Lomakin .................................................................... 402 Methods of Stochastic Mechanics for Characterisation of Microstructural Failure in Heterogeneous Materials: Mikhail Tashkinov, Natalia Mikhailova ............................................................................................ 403 The complex experimental studies of the mechanical properties of reinforcing elements: Maria S. Temerova, Valeriy E. Vildeman, Evgeniy V. Lomakin ......................................................................................... 404 Shock loading direction effects on ejection mass and particle sizes of micro-jet from a grooved metal surface: Shi Yi-na, Qin cheng-sen ....................................................................................................................... 404 21 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Poster Topic H: Materials for fission and fusion  XRD examination of oxide dispersion strengthened steels irradiated by swift heavy ions: Andrei Benediktovitch, Vladimir Uglov, Svetlana Vlasenko, Tatiana Ulyanenkova, Alexander Sohatsky, Jacques O’Connell, Vladimir Skuratov ............................................................................................................ 407 Creep and anelasticity of ferritic ODS steel MA956: José Rodolpho de Oliveira Leo, Amir Shirzadi, Jan Kowal, Michael E. Fitzpatrick ...................................................................................................................... 407 Application of Automated Ball Indentation Innovative Technique on the Determination of Mechanical Properties of Nuclear Structural Materials: Jan Štefan, Radim Kopřiva, Jan Siegl ............................................ 408 Radiation stability of ZrSiN system under the Xe ions irradiation: Vladimir Uglov, Vitali Shymanski, Gregory Abadias, Gennagy Remnev, Andrey Suvalov ...................................................................................... 409 Poster Topic I: High temperature materials   Atomistic Simulations of Dislocation-Interface Interactions in the γ/γ’ Microstructure in Ni-base Superalloys: Frederic Houlle, Juan Wang, Julien Guenole, Johannes J. Möller, Aruna Prakash, Erik Bitzek ........................................................................................................................................................... 411 Internal Friction and Shear Modulus Temperature Dependence of 9%Cr Ferritic Steel P92 in 25 ÷750°C Temperature Range: Elguja Kutelia, George Darsavelidze, Tengiz Kukava, Temur Dzigrashvili, Ia Kurashvili, Francisco J. Perez Trujillo ....................................................................................................... 412 Poster Topic K: Polymer based composites Research of the Processing Parameters of Three-dimentional Printer and the Product: Kunihiro Araki, Goshi Hamabe, Tatsuya Tanaka, Yoshihiko Arao ............................................................................................... 414 Supervised Estimation of the Local Glass Fiber Content from 2D X-ray Imaging of Plate-like Parts made from Sheet Molding Compounds: Benjamin Bertram, Kay André Weidenmann .............................................. 414 Deformation and fracture of aircraft fibrous polymer composites in external actuating factors and high temperature mechanical tests: Dmitrii S. Lobanov, Valeriy E. Wildeman, Evgeniy V. Lomakin ........................ 415 Numerical simulation for developing grounds in support of application of fiber optic sensors for monitoring of composite materials: Valery P. Matveenko, Grigoriy S. Serovaev, Valery, V. Korepanov, Nataliia A. Yurlova, Aleksandr N. Anoshkin, Anatoliy A. Tashkinov, Gleb S. Shipunov, Valeriy Y. Zuyko .....416 Poster Topic L: Lightweight alloys and structures   Ab-initio coarse-grained approach for modeling the two-dimensional packing structure of solute nanoclusters in Mg-based LPSO phases: Hajime Kimizuka, Shigenobu Ogata ................................................... 419 Surface Nitriding of Titanium Using Atmospheric-controlled IH-FPP Treatment. Ota Shumpei, Murai Kazue, Omiya Msaki, Komotori Jun, Fukazawa Kengo, Misaka Yoshitaka, Kawasaki Kazuhiro .................................. 420 Poster Topic X: General mechanical behavior Thermal ageing effect on mechanical behavior of polycarbonate: Hamid Bbabou, Ferhoum Rabah, Meziane Aberkane .............................................................................................................................................. 422 Effect of Ultra-violet radiation on the mechanical behavior of PMMA (polymethyl methacrylate): Amirat Boukhalfa, Ferhoum Rabah .................................................................................................................. 422 Dynamic Mechanical Properties of Cortical Bone Depend on Bone Mineral Content: Zude Feng, Ting Wang ........................................................................................................................................................... 423 Study of concretes and mortars made with metallic fibers: Souad Kherbache, Karim Moussaceb, Nedjima Bouzidi, A. kader Tahakourt .............................................................................................................................. 424 Effect of Strain-Rate on Tensile Properties of Nuclear Piping Materials at RT and 316oC. Jin Weon Kim, Myung Rak Choi ................................................................................................................................................. 424 22 Contents Variation of Mechanical Properties in the Pipe Bends Fabricated by High-frequency Induction Bending: Jin Weon Kim, Mi Yeon Lee, Young Jin Oh, Heung Bae Park, Kyung Su Kim, Tae Soon Kim .............................. 425 Modeling and observation of compressive behaviors of anisotropic aluminum cellular structures based on the Voronoi tessellation concept: Sang-Youn Park, Byoung-Ho Choi, Seung Ki Moon, Il-Hyuk Ahn .........426 Influence of the addition of cooked and crushed clay on the mechanical strength of a self-compacting concrete: Fatiha Soudi, Nasser Chelouah, Tiziri Bezzi ...................................................................................... 427 Retained Austenite: Non Destructive Analysis by using X-Ray according to ASTM 975-03: M. Michiel van der Mey ........................................................................................................................................................ 428 23 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Plenary Talks 24 Plenary Talks The treatment of residual stresses in fracture mechanics cal- culations Bob Ainsworth The University of Manchester, Manchester, UK Fitness-for-purpose assessments of engineering com- the prior plastic straining which occurs either during ponents are required in order to demonstrate defect the welding process or as a result of subsequent load- tolerance and the ability to continue to operate safely ing, such as during pre-service proof loading. Consid- (Zerbst et al 2003). Such assessments are particularly eration is limited to the influence of prestrain on duc- required for welded regions as these are susceptible tile fracture. Both uniform plastic straining (Ainsworth to flaws and contain residual stresses which may con- 1986b) and recent studies on highly non-uniform tribute to structural failure (Zerbst et al 2014). The as- straining, such as occurs if a defect is present during sessments need inputs from both stress analysis and the proof loading for example, are addressed. It is materials properties. shown that non-uniform prestrain may significantly For the stress analysis, loadings can be both prima- complicate the measurement of representative frac- ry, such as pressure and dead-weight, and secondary, ture toughness values. such as the residual stresses at weldments. In the elastic region, primary and secondary stresses are References simply added linearly to calculate the total stress in- Ainsworth, R. A. (1986a): The treatment of thermal tensity factor. However, the relative contributions of and residual stresses in fracture assessments. Engng the primary and secondary loads to the total crack Fract Mech 24, 65-76. driving force change during the loading sequence as Ainsworth, R. A. (1986b): An assessment of the effects plasticity develops. In particular, the secondary stress of prestrain on upper shelf fracture toughness. J becomes much less significant when gross yielding oc- Strain Analysis 21, 219-223. curs (Ainsworth 1986a). However, if the crack tip plas- Zerbst, U., Schwalbe, K.-H. & Ainsworth, R. A. (2003): tic zone remains surrounded by elastic material at high An overview of failure assessment methods in codes remote stresses this can lead to an increase in the con- and standards. Chapter 7.01 in Comprehensive Struc- tribution of the secondary stresses to the crack driving tural Integrity (Eds I Milne, R O Ritchie, B Karihaloo), force (Ainsworth 2012). Such cases are referred to as Elsevier, Oxford. exhibiting elastic follow-up. This paper describes how Ainsworth, R. A. (2012): Consideration of elastic fol- the contribution of secondary stresses can be included low-up in the treatment of combined primary and in fitness-for-purpose assessments, including recent secondary stresses in fracture assessments. Engng developments which allow the treatment of cases ex- Fract Mech 96, 558-569. hibiting elastic follow-up. Zerbst, U., Ainsworth, R. A., Beier, H.-TH., Pisarski, Weldments are not only regions of high residual stress- H., Zhang, Z.L., Nikbin, K., Nitschke-Pagel, T., Mün- es but are also often regions of low fracture toughness stermann, S., Kucharczyk, P. & Klingbeil, D. (2014): properties. The paper therefore also addresses the Review on fracture and crack propagation in weld- fracture toughness input to fitness-for-purpose assess- ments – a fracture mechanics perspective. Engng ments and specifically how this may be influenced by Fract Mech 132, 200-276. X-Mechanics for Metal Plasticity W. A. Curtin Institute of Mechanical Engineering, Ecole Polytechnique Federale de Lausanne, Switzerland The application of X-Mechanics (X= quantum, atomis- requires application of X-Mechanics for both qualita- tic, statistical, dislocation, mesoscale, and continuum) tive and quantitative models of plastic flow as a func- to elucidate the mechanistic origins of plasticity phe- tion of alloying, temperature, strain-rate, grain size, nomena is emerging as a powerful paradigm for predic- and including size effects in plasticity. tive metallurgy. In particular, the structure of disloca- Here, we start with a brief overview of recent work at tions and the interactions of dislocations with solutes, the quantum, atomistic, and statistical scales aimed at precipitates, other dislocations, and grain boundaries, quantitative prediction of yield strength in Al and Mg 25 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 alloys. The onset of macroscopic plastic flow can be We have recently extended the 2d mesoscale disloca- predicted without recourse to higher-level modeling. tion dynamics models to include elements of 3d “forest Such studies also provide “inputs” to higher-level mod- hardening” and, thus, strain hardening phenomena. els, and can guide the formal structure of such models. This yields model systems with tunable yield strength We then move to mesoscale dislocation dynamics in and work-hardening, to enable study of the interplay 2d plane strain, but in the presence of pinning obsta- of these mechanisms in mesoscale deformation. How- cles typical of metal alloys. We present a new concept, ever, this method will not be discussed in detail in this “stress gradient plasticity”, that emerges naturally talk. from the analysis of dislocation pile-ups under a spatial We conclude with discussion on how to bridge be- stress gradient.1 The analysis shows that the spacing tween the smaller- and larger-scale X-Mechanics meth- between pinning obstacles is a material length scale ods. The key issue is whether smaller-scale X-Mechan- that can give rise to size-scale effects in the presence ics simply provides inputs into existing higher-scale of stress gradients. Discrete dislocation models clearly X-Mechanics models or provides guidance for entirely demonstrate the stress gradient plasticity phenome- new higher-scale X-Mechanics models. non and the role of obstacle spacing. “Stress gradient plasticity” is then implanted within a low-order con- References tinuum plasticity framework and is shown to predict Chakravarthy, S.S. & Curtin, W. A. (2011): Proc. Natl. size effects in bending, torsion, indentation, and void Acad. Sci. 108, 15716-15720. expansion. The model is applied to explain experimen- tal size effects – both strengthening and hardening – in recent bending and torsion experiments in pure poly- crystalline metals. Materials for ultra high-temperature applications Haruyuki Inui, Kyosuke Kishida, Norihiko L. Okamoto Kyoto University, Kyoro, Japan There are various applications for structural materials mary concern. The material should not lose the body used at high and ultra-high temperatures. Of these by oxidation in a severe oxidizing environment at very applications, turbines for land-based power genera- high temperatures. That means the material should tion and aircraft jet engines may be one of the typical form protective oxide scales during oxidation. When examples. For these applications, there is an ever-in- judged from the so-called Ellingham diagram, Al and creasing demand for efficiency improvement, in order Si are known to readily form thermodynamically very to reduce fuel consumption and CO2 gas emission. The stable oxides with a slow growth rate. This means that efficiency of a gas turbine combined cycle power plant alumina and silica can be a protective oxide scale and can be improved by increasing the turbine inlet tem- that the material of our concern should contain either perature. There is, therefore, a very strong demand for Al or Si in a good quantity for better oxidation resist- structural materials that can withstand for these very ance. On top of that, the material should have some high temperatures. The turbine inlet temperature has dislocation activity to achieve some allowable value increased year by year so that gas inlet temperature is of toughness. Dislocation properties are obviously in- always higher than the temperature capability of ma- fluenced by the lattice periodicity, as Peierls evaluated terial, indicating that the materials cooling is essential. the stress required for dislocation to overcome the po- Material cooling usually leads to the efficiency loss of tential barrier a long time ago. The lower Peierls stress a combined cycle engines by a few to several %. So, may lead to a higher dislocation mobility, and hence materials that can be used without cooling is badly de- the higher fracture toughness. Then, simple crystal sired. New high-temperature materials that can with- structures are naturally beneficial to high dislocation stand very high temperatures exceeding the upper lim- mobility, and hence the higher fracture toughness. it of Ni-base superalloys are strongly demanded. In that sense, intermetallics with superlattices based Generally speaking, high strength and high tough- on either FCC, BCC or HCP structures, especially alu- ness is a primary concern as the properties required minides and silicides formed with transition-metal can for high-temperature structural materials, although be strong candidates. these two are in the pay-off relation. Light weight is In the presentation, the current status for the devel- sometimes very important especially when used in a opment of high-temperature structural silicide and rotating part, since the centrifugal force is proportional aluminides will be reviewed, after the introduction to to the weight. High oxidation resistance is another pri- high-temperature structural materials. 26 Plenary Talks Materials Innovation for Nuclear Energy - Super ODS Steels R&D Akihiko Kimura1*, Wentuo Han1, Hwanil Je2, Yoosung Ha2, Hiroyuki Noto2, Dongsheng Chen2, Nori- yuki Iwata1, Ryuta Kasada1, Takanari Okuda3, Shiheharu Ukai4, Masayuki Inoue5, Peng Dou6, Sang- hoon Noh7 1 Institute of Advanced Energy, Kyoto University, Kyoto, Japan 2 Graduate School of Energy Science, Kyoto University, Kyoto, Japan 3 KOBELCO Research Institute, Kobe, Japan 4 Hokkaido University, Sapporo, Japan 5 Japan Atomic Energy Agency, Tokaimura, Ibaragi, Japan 6 Chongqing University, Chongqing, China 7 Korea Atomic Energy Research Institute, Daejon, Korea Materials development is essential for realization of TEM/EDS observations, high temperature XRD meas- advanced nuclear fission reactors as well as fusion urements and analyses by FE-EPMA and FE-AES. Chem- DEMO reactors and beyond. High performance struc- ical compositions of the main particles in Al-added ODS tural materials R&D has been conducted for the last steel were influenced by addition of small amount of several decades and there have been made some re- Zr, which resulted in the formation of (Y, Zr) oxide parti- markable technology innovations of nuclear structural cles rather than (Y, Al) oxide particles. The size and the materials [1]. number density of Zr-added steel was reduced and in- Among the candidate nuclear and blanket structural creased, respectively. The coherency of the (Zr, Y) oxide materials, oxide dispersion strengthened (ODS) steels, particles depended on the size of the particle. Charac- which have been produced by means of “mechanical teristic features of the oxide particles in strengthening alloying”, are considered to be promising for advanced mechanism is summarized for the ODS steels. nuclear systems with high thermal efficiency, because In this presentation, current status of ODS steels R&D the ODS steels have high-strength at elevated temper- in Japan is also summarized and the impacts of some atures and good resistance to corrosion and irradiation material innovations on the safety issue of nuclear degradation. The operation temperature can be elevat- technologies are addressed. Radiation tolerance mech- ed up to 700 °C. Radiation tolerance was considerably anism of advanced ferritic steels is introduced in terms improved by a dispersion of nano-scaled oxide parti- of trapping capacity for radiation defects caused by cles. nano-scaled ultra-fine oxide particles dispersion. Fur- There are several sorts of ODS steels with different thermore, the recent experimental results on mechan- Cr contents: (9-12)Cr-ODS ferritic/martensitic steels ical properties at elevated temperatures, corrosion be- [2] and (14-16)Cr-ODS ferritic steels with and without havior in SCW and LBE and phase stability under ion Al addition [3]. The former two groups of ODS steels irradiation of ODS steel are shown to demonstrate that were developed for application to sodium cooled fast the ODS steels with nano-scaled oxide particles in high reactors and fusion reactors, and the last group of ODS number density are promising for the fuel cladding ma- steels were for so-called Generation IV fission nuclear terial of next generation nuclear systems. reactors. More recently, accident tolerant fuel R&D is progressing to apply high Cr-high Al ferritic steels to fuel References cladding of light water reactor because of “Fukushima [1] A. Kimura, R. Kasada, N. Iwata, H. Kishimoto, T. Incident”. It has been considered that the replacement Okuda, M. Inoue, S. Ukai, T. Fujisawa, T.F. Abe et al., of Zirconium alloys cladding with high-performance (2011): J. Nucl. Mater. 417, p176-179. ferritic steels cladding may retard the hydrogen gen- [2] S. Ukai, T. Nishida, H. Okada, T. Okuda, M. Fujiwara eration at a severer accident (SA) of nuclear reactors, and K. Asabe, (1997): J. Nucl. Sci. Technol., 34[3], resulting in a large time lag up to hydrogen explosion. p256. High performance of ODS steels stems from the fine [3] A. Kimura, S. Ukai and M. Fujiwara, (2003): Proc. nano-scaled oxide particle dispersion. Dispersion mor- Int. Conf. On Grobal Environment and Advanced phology of the oxide particles, such as size, number Nuclear Power Plants, (GENES4/ ANP2003) ISBN: density, chemical compositions and coherency be- 4-901332-01-5, CD-ROM file, p. 1198. tween matrix and particles, are characterized by FE- 27 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Tensile and fatigue behavior of steels in high pressure hydro- gen gas atmospheres Hisao Matsunaga1, 2, 3, Junichiro Yamabe2, 3, 4, Saburo Matsuoka2 1 Department of Mechanical Engineering, Kyushu University, Fukuoka, Japan 2 Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University, Fukuoka, Japan 3 International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Fukuoka, Japan 4 International Research Center for Hydrogen Energy, Kyushu University, Fukuoka, Japan In preparation for the forthcoming commercializa- In this study, the following tests were conducted on a tion and subsequent world-wide adoption of fuel-cell variety of steels; austenitic stainless steels with various vehicles and hydrogen stations, a specialized set of austenitic stabilities, a quenched-and-tempered Cr-Mo components (e.g., vessels, valves, regulators and me- steel and an annealed carbon steel, in high-pressure tering devices) is being developed for the handling of hydrogen gas up to 115 MPa. high-pressure hydrogen gas. The degree of susceptibil- 1. Slow strain rate tensile (SSRT) tests ity of materials to hydrogen embrittlement (HE) greatly 2. Tension-compression fatigue tests using smooth influences their possible selection and qualification for specimens use with high-pressure hydrogen gas. This is because 3. Fatigue crack growth tests using compact tension HE is a potentially dangerous phenomenon known to (CT) specimens be dependent on various factors such as material type, The experimental results manifest the susceptibility of hydrogen gas pressure, temperature and loading con- the strength properties of these steels to high-pressure ditions. hydrogen gas, as well as the microscopic mechanism of NASA categorized numerous metallic materials into degradation associated with hydrogen-enhanced crack four specific grades according to their individual sus- growth. Finally, simple requirements are proposed for ceptibility to high-pressure hydrogen (NASA 2005). the qualification of metallic materials used under de- For instance, austenitic stainless steels with FCC struc- sign by rule (fatigue limit design) and design by analysis ture (e.g., types 316, 310 and 304ELC) are categorized (fatigue life design) for hydrogen service. in the guidelines as being “negligibly-embrittled” or “slightly-embrittled” and, therefore, are widely used Reference for various components exposed to hydrogen gas. On National Aeronautics and Space Administration. the other hand, martensitic and ferrite-pearlite steels (2005): Safety standard for hydrogen and hydrogen with BCT/BCC structure (e.g., AISI 1042 and AISI 1020) systems, NSS 1740.16. are categorized as being “severely-embrittled” or “extremely-embrittled”, due to such a high degree of Acknowledgements susceptibility. Therefore, the use of BCT/BCC steels in This work was supported by the New Energy and Indus- high-pressure hydrogen gas environments is highly re- trial Technology Development Organization (NEDO), stricted under current regulations and standards. How- Fundamental Research Project on Advanced Hydrogen ever, with the widespread commercialization of hydro- Science (2006 ~ 2012) and Hydrogen Utilization Tech- gen energy systems, BCT/BCC steels are also likely to be nology (2013 ~ 2018). used extensively for hydrogen service so as to reduce production costs. Deformation, Fatigue, and Fracture of Ultrafine Grained and Nanocrystalline Materials A. Hohenwarter2, T. Leitner2, O. Renk1, C. B. Yang, M. Kapp1, L. Krämer1, P. Gupta1, V. Maier1, R. Pippan1,2, 1 Erich Schmid Institute of Austrian Academy of Sciences and 2 Department of Material Physic University Leoben, Austria Tensile, fatigue and fracture mechanics properties of quantities. This enables us to determine the fatigue nanocrystalline materials are rare, because the avail- properties, ductility and fracture toughness of these able material volume is usually very small. Severe types of materials. High pressure torsion allows SPD of plastic deformation (SPD) is a new method to produce most metallic materials. Hence, it allows to transform ultrafine grained or nanocrystalline materials in larger the typical microcrystalline materials to an ultrafine or 28 Plenary Talks nanocrystalline state. The large HPT equipment at our tained results in pure metals, alloys, and nanocompos- institute permits now to determine standard tension ites. Special attention will be devoted to the developed and fracture mechanic tests on a large variety of metals anisotropy of the fracture toughness, which is in some and alloys. The paper will give an overview of the ob- materials extremely pronounced. Damage Tolerance in Natural and Bioinspired Structural Ma- terials Robert O. Ritchie1,2 1University of California, Berkeley, CA, USA 2Lawrence Berkeley National Laboratory, CA, USA The attainment of both strength and toughness, i.e., Here we focus on the mechanistic basis for the me- damage tolerance, is invariably a vital requirement chanical properties of several natural materials, name- for structural materials; unfortunately in many mate- ly bone, tooth dentin and nacre in seashells which rial classes these properties can be mutually exclusive are prime examples of natural materials that are truly (Ritchie 2011). Accordingly, the development of dam- damage-tolerant (Launey et al. 2011), fish scales which age-tolerant engineering materials has traditionally are designed as natural flexible dermal armors combin- been a compromise between hardness vs. ductility. ing hard surface layers with a tough (and adaptable) Natural materials often display excellent strength and subsurface region (Yang et al. 2013), and skin with its toughness (in relative terms) even though they are syn- remarkable resistance to tearing and fracture. (Yang et thesized at ambient temperatures from a fairly limited al. 2015). palette of constituents, often with relatively meagre We further examine attempts to make synthetic com- properties. Nature’s structures, however, usually com- posites in the image of such natural materials, though prise both hard and soft phases arranged in complex hi- in general the large span in length-scales and overall erarchical composite architectures, with characteristic complexity of most biological materials impose combi- dimensions spanning from the nanoscale to the macro- nations of requirements and design motifs that make scale. The result can be materials that are lightweight the development of new biomimetic materials gen- and often multi-functional, which can display unique erally well beyond the reach of present technologies. combinations of mechanical properties that are gener- We do describe, however, several examples where ally far superior to those of their constituents, but are one technique, freeze-casting has been used to make difficult to replicate synthetically (Wegst et al. 2015). “compliant-phase” ceramic composites in the image of In this work, we seek the inspiration of biology to nacre with exceptional damage tolerance (Munch et al. discern strategies for the development of new engi- 2008), although this and most of the other current pro- neering structural materials with enhanced damage cessing techniques are still not feasible for large-scale tolerance. We focus on the interplay between the in- materials production. dividual nano/micro-mechanisms that contribute to strength and toughness, that of plasticity and crack-tip References shielding, noting that these phenomena originate at Launey M.E., Buehler M.J. & Ritchie R.O. (2011): On very different structural length-scales – strength at the the mechanistic origins of toughness in bone. Ann. nano to micro scales, toughness primarily at the micro Rev. Mater. Res., 40: 25-53. to macro scales. The lessons from Nature are particu- Munch E., Launey M.E., Alsem D.H., Saiz E., Tomsia larly relevant as natural materials can display unusual A.P. & Ritchie R.O. (2008): Tough bio-inspired hybrid combinations of properties that derive from these dif- materials. Science, 322: 1516-1520. fering length-scales because of their multi-dimensional Ritchie R.O. (2011): The conflicts between strength hierarchical architectures with precisely engineered and toughness. Nature Materials, 10: 817-822. interfaces. Our objective is that by mimicking these Wegst U.G.K., Bai H., Saiz E., Tomsia A.P. & Ritchie natural structural architectures, identifying the salient R.O. (2015): Bioinspired structural materials. Nature strengthening and toughening mechanisms over mul- Materials, 14: 23-36. tiple length-scales, and most importantly finding ways Yang W., Chen I.H., Gludovatz B., Zimmermann E., to actually make these bioinspired materials in bulk Ritchie R.O. & Meyers M.A. (2013): Natural flexible form, that we can develop new lightweight structural dermal armor. Adv.. Mater., 25: 31-48. materials where the strength vs. toughness “conflict” Yang W., Sherman V.R., Gludovatz B., Schiable E., has been solved to achieve exceptional levels of dam- Stewart P., Ritchie R.O. & Meyers M.A. (2015): Ex- age-tolerance. traordinary tear resistance of skin. Nature Comm., in press. 29 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 TALKS 30 Talks Topic A 1: Multiscale phenomena in plasticity Talks Topic A1: Multiscale phenomena in plasticity 31 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Atomistic Simulations as Bridge between Experiments and Mesoscale Models: a Case-Study on Dislocation-Precipitate Interactions in Ni-base Superalloys Erik Bitzek Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Department of Materials Science and Engineering, Germany To study the mechanical properties of a specific ma- A novel technique was developed to reconstruct an at- terial or class of materials, mesoscale models like dis- omistic sample from an APT experiment on the alloy location dynamics (DD) or phase field simulations re- ERBO/1. The curvature of the reconstructed precipi- quire quantitative information on the properties of the tate leads to the formation of a misfit dislocation net- defects of interest. While some information like the work (MFDN), which is significantly different from the shape and arrangement of precipitates are readily ob- MFDN obtained for a planar interface. Unlike the con- tained by experiments, other properties like dislocation stricted misfit dislocation cores obtained in the usual mobilities or interface energies require more involved 2D setups, the misfit dislocations can dissociate, and experiments and analysis. Some material parameters the overall network structure is reminiscent of the in- like unstable stacking fault energies, however, can not terfacial dislocation network formed during the initial be determined experimentally. Atomistic simulations, stages of creep, see e.g. (Agudo Jacome et al. 2013), either based on density functional theory (DFT) or on and contains the same Burgers vectors and line direc- semi-empirical potentials, are ideally suited to calcu- tions. Simulations of the interaction of one and two 60° late many of these material parameters. Yet, the sim- channel dislocations with the MFDN reveal typical pro- ulation setups used to study atomic scale deformation cesses also observed in experiments like the knitting processes are in most cases highly idealized. While out of dislocations from the MFDN and the cutting of this is often necessary in order to quantitatively deter- the precipitate by a pair of channel dislocations. These mine certain material properties, overly simplified or results cannot be obtained with simulation setups that constricted setups might artificially supress important were previously used in the literature. As APT does not deformation mechanisms. only provide information on the sample morphology Here we present an example of how using atom probe but also on its chemical composition, the simulations tomography (APT) data can lead to more realistic at- were performed using stoichiometric Ni/Ni3Al as well omistic samples which show significantly different as with representative local concentrations of Ni, Al properties and deformation processes compared to and Re, thus allowing to asses the role of chemical the usually used simulation setups. The atom probe composition on the dislocation – precipitate interac- informed atomistic simulations in turn provide impor- tions. In addition to the qualitative information gleaned tant insights and material parameters for DD models. from the simulation on the reconstructed APT sample, The present example is centered on the study of dis- quantitative information on dislocation mobility and location processes in the γ/γ’ microstructure of single the critical cutting stress necessary for dislocations to crystalline Ni-base superalloys. The superior high-tem- penetrate the γ’-phase was obtained on 2D samples perature mechanical properties of these superalloys with representative local chemical compositions and is a direct consequence of this microstructure which passed on to DD simulations. consists of a high volume fraction of the cuboidal L12 ordered γ’-phase that is precipitated in a disor- References dered face-centered cubic γ-matrix. Such precipitate Agudo Jácome, L. et al. (2013) High-temperature and strengthened alloys are much stronger than the indi- low-stress creep anisotropy of single-crystal superal- vidual phases, and the strengthening effect is believed loys. Acta Mater. 61, 2926–2943. to mainly arise from the difficulty of channel disloca- tions in the γ-phase to cut into the γ’-precipitate. 32 Talks Topic A 1: Multiscale phenomena in plasticity Accelerated molecular dynamics study of grain boundary motion and dislocation nucleation from grain boundary Shigenobu Ogata1,2, Akio Ishii1, Yunjiang Wang3, Junping Du1 1Osaka University, Osaka, Japan 2Kyoto University, Kyoto, Japan 3Chinese Academy of Sciences, Beijing, China Grain boundary motion and dislocation nucleation motion was successfully accelerated, and we found a from grain boundary are key deformation units to un- sharp mechanism transition from displacive to diffu- derstand plastic deformation properties of nano-crys- sive motions with increasing temperature in several talline metals because of the less intra-grain dislocation grain boundaries, such as a sliding and migration cou- activities in the nano-grains. Since these deformation pled grain boundary motion at low temperatures less units are atomistic scale events and consist of ther- than ~500K and a decoupled motion above ~500K. The mally-activated processes at finite temperature, we latter was mainly driven by local atomic diffusion in the need to perform an atomistic simulation, like molecu- grain boundary. We estimated temperature dependent lar dynamics (MD) simulation, at finite temperature to activation volume of the grain boundary motion and obtain atomistic, kinetic and energetic details of these found that the activation volume sharply changed at events. However, it is difficult to find and analyze them the mechanism transition temperature. Next, we ap- at finite temperature and at usual experimental strain plied this method to dislocation nucleation from grain rates using conventional MD simulation method, be- boundary. Again, dislocation nucleation event from cause these are rare events in a typical MD time-scale. grain boundaries was successfully accelerated and ob- Recently, we have developed an accelerated MD simu- served in the MD simulation. Then, we analyzed tem- lation method (Ishii et al. 2012), that is called adaptive perature and stress dependent activation free energy boost MD method, and we have applied this method and activation volume, and based on them, we also to investigate a carbon diffusion (Ishii et al. 2012) and studied temperature and strain rate dependencies of a dislocation motion with solute atom (Ishii et al. 2013) critical stress of the dislocation nucleation. in iron, and demonstrated that the adaptive boost MD method can successfully accelerate these rare events References and provide atomistic event details, kinetics and ener- Ishii, A., Ogata, S., Kimizuka, H. & Li, J. (2012): Adap- getics. tive boost moelcular dyanmics simulation of carbon In this study, we applied this method to investigate the diffusion in iron, Physical Review B, 85-6, 064303. grain boundary motion and dislocation nucleation from Ishii, A., Li, J. & Ogata, S. (2013): ``Conjugate chan- a grain boundary. First we analyzed a behavior of sever- neling“ effect in dislocation core diffusion: carbon al grain boundaries in copper crystal under shear strain transport in dislocated BCC iron, PLoS ONE, 8-4 along the grain boundaries. Actually grain boundary (2013), e60586. Ab initio-based atomistic model simulation of deformation and fracture in SiC power device Yoshitaka UMENO1, Atsushi KUBO1, Shijo NAGAO2 1Institute of Industrial Science, The University of Tokyo, Japan 2The Institute of Scientific and Industrial Research, Osaka University, Japan SiC, which is semiconducting crystal having wider ulations to reveal the mechanism behind such defor- bandgap than that of Si, is one of the most promis- mation. ing materials for power semiconductor device. Major In fact, there have been some studies on the deforma- challenges toward application include cracking dur- tion in SiC using atomistic model simulation such as ing manufacturing process due to thermal stress and molecular dynamics. However, interatomic potentials stacking fault growth brought by migration of Shockley suggested thus far for SiC were constructed without partial dislocations around PN junction in operation. It taking into account the strong anisotropy of the crys- is therefore required to perform atomistic model sim- tal strength and the effect of multiaxial loading condi- 33 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 tions. To perform reliable atomistic-model simulations, in 3C, has different arrangement according to the crys- it is necessary to construct an interatomic potential tal structure. Our simulations also demonstrated that that can describe such aspects. both cleavage and slip can occur at the atomistic scale In this study, we firstly performed ab initio density although SiC is macroscopically brittle. functional theory (DFT) calculations to obtain ideal 　An analysis of shear deformation of a model contain- shear and tensile strength of SiC to develop an inter- ing Shockley partial dislocations revealed that electric atomic potential function based on the obtained DFT environment can alter the mobility of the two kinds data. Then, we carried out molecular dynamics simu- of dislocation core (Si- and C-cores). When negatively lations of deformation of SiC crystal under mechanical charged, the order of their mobilities can be reversed. loading using the develped interatomic potential. This result explains the contradiction between a cal- We employed the Angular-Dependent Potential (ADP) culation with the Tight-Binding method (where C-core model for the interatomic potential function. An ad- moved) and an experimental observation (where Si- ditional term for pairwise interaction is include in the core moved) and provides an important insight to the model to describe the Coulomb interaction, which mechanism of expansion of stacking faults under elec- should play an important role in SiC. Potential param- tric current. eters are fitted using the Force-Matching method for This work was supported in part by the Network Joint better transferability. The developed potential can Research Center for Materials and Devices. successfully reproduce the ideal strength, the effect of superimposed multiaxial loading on the strength and References phase transition under compression. Y. Mishin et al., Acta Mater. 53.15 4029 (2005). 　Our molecular dynamics simulations of tension of F. Ercolessi et al., Europhys. Lett. 26.8 583 (1994). thin film models of 3C-SiC and 4H-SiC showed that dif- A. T. Blumenau et al., J. Phys.: Condens. Matter 14.48 ferent deformation modes appear in the two models 12741 (2002). because the crystallographic plane that possesses the M. Skowronski and S. Ha, J. Appl. Phys. 99.1 011101 lowest strength against tension, (0001) in 4H and (111) (2006). Research on constitutive model of nickel-based superalloy and the numerical simulation during superalloy blade cold rolling process Xiangwei Kong1, Wenran Geng2, Chunlin Qiu3 1 School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China 2 CFHI Dalian International Tech & Trade Co. Ltd., Dalian,Liaoning Province, China 3 State Key of Laboratory of Rolling Technology and Automation, Northeastern University, Shenyang, China In recent years, cold rolling as a new technology has Then, the numerical simulation of blade rolling process been widely applied in the field of aviation blade manu- was implemented using the software DEFORM-3D em- facture because it has many advantages, such as stable bedded with the established constitutive model. working process, small equipment tonnage, fine work- In order to descript severe plastic deformation accu- piece mechanical properties and high production effi- rately, the Yoshida-Uemori constitutive model (Yoshi- ciency (Chaboche 2008). However, very few researches da 2002 and 2003) was employed in our study. The me- are focused on the blade rolling process because of the chanical properties of nickel-based superalloy GH4169 complexity of blade shape and the difficult-to- defor- was performed under different conditions at ambient mation of blade superalloys. The control of technical temperature to obtain the material parameters of the schedule and mould shape of blade rolling process is constitutive model. The secondary development of DE- totally dependence on the experiences. The blasd pol- FORM is carried out using the established constitutive ishing method and mould adjustment also mainly de- model o GH4169. Comparing the numerical simulation pend on the manual operation. Under such condition results with the results of cuboid compression test, the the production efficiency and the product quality are maximum error is lower than 1.1% for the GH4169. This not guaranteed. Therefore, the material flow behav- verifies that the new constitutive model for GH4169 is ior and forming mechanism of blade rolling process suitable for simulating the blade rolling process. The should be further investigated to optimize the design flow rule of blade metal during the process is that the of mould and the selection of technical parameters. In forward and back slip zones is not homogeous along this working, the constitutive model of superalloy was the transverse direction of blade. estabished according to the flow stress of materials. This work exhibits a new idea for the study on the form- 34 Talks Topic A 1: Multiscale phenomena in plasticity ing law, the optimization of moulds and the selection Yoshida F., Uemori, T.(2002): A model of large-strain of technique parameters during variable cross-section cyclic plasticity describing the Bauschinger effect rolling process. and workhardening stagnation, International Jour- nal of Plasticity, 18: 661-686; Hiroshima References Yoshida F, Uemori T. (2003): A model of large-strain Chacoche J.L. (2008): A Review of Some Plasticity and cyclic plasticity and its application to springback Viscoplasticity Constitutive Theories, International simulation, International Journal of Mechanical Journal of Plasticity, 24: 1642-1693; Troyes. Sciences, 45:1687-1702; Hiroshima. Development of Mechanism-Based and Microstructure-Sen- sitive Modeling Approach to Plastic Deformation in Multi- Phase Alloys Duchao Lv, Pengyang Zhao, Don McAllister, Stephen Niezgoda, Michael Mills, Yunzhi Wang Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio, USA The key to predicting, and therefore optimizing, prop- most conservative) property set over an entire compo- erties of materials is the knowledge of the state of nent, next generation modeling tools that incorporate microstructure. Figure 1 shows a typical example of specific deformation mechanisms operating in specific dramatic change in creep mechanism from disloca- alloy systems under a given set of processing parame- tion-based creep in the bore region to the remarkable ters, microstructure states and service conditions are microtwinning process in the rim region observed in desperately needed. an ME3 turbine disk for identical deformation condi- In this presentation, using plastic deformation in Ni- tions (Kovarik2009). The sensitivity of creep response base superalloys as an example, we show how to in- to subtle changes in microstructure and the need for tegrate mesoscale modeling (phase field (Wang2010)) location-specific microstructure optimization in a tur- with experimental characterization to bridge ab initio bine disk are quite obvious. calculations and image-based crystal plasticity (CP) simulations to (a) identify deformation mechanisms, quantify activation pathways, and provide deformation mechanism maps (DMMs) as function of alloy composi- tion, processing, microstructure and loading condition (Unocic2011; Zhou2011), (b) develop a fully integrated phase-field + FFT-CP modeling approach to simultane- ous polycrystalline and precipitate microstructure evo- lution and dislocation density evolution during creep, which incorporates the DMMs obtained from (a), and (c) develop a continuum level FEM for macroscopic re- sponse, which incorporates the deformation behavior of individual RVEs obtained from (b). Fig. 1: Strong dependence of monotonic creep response as References a function a subtle microstructure differences between the Kovarik, L. (2009): Microtwinning and Other Shearing bore and rim of an actual disk forging for ME3. Mechanisms at Intermediate Temperatures in Ni- Base Superalloys – In Prog. Mat. Sci. 54: 839-873. In the past decade, unprecedented methods to quan- Wang, Y. and J. Li (2010): Acta Materialia Overview tify, use and explore grain- and precipitate-scale mi- 150: Phase Field Modeling of Defects and Deforma- crostructures have been developed. However, most tion in Acta Mater. 58: 1212-1235. modeling approaches to microstructure-property re- Unocic, R, N. Zhou, L. Kovarik, C. Shen, Y. Wang, and lationship utilize highly simplistic descriptors of micro- M.J. Mills (2011): Evolution of Deformation Microt- structures (such as average particle size and volume wins during Creep of a g’ Precipitate Strengthened fraction) that are empirically correlated to the prop- Ni-Base Superalloy in Acta Mater. 59:7325-7339. erties (e.g., cutting vs. looping). Such approaches are Zhou, N., C. Shen, M.J. Mills, J. Li and Y. Wang (2011): utterly inadequate for addressing the design needs. To Modeling Displacive-Diffusinal Coupled Dislocation enable location-specific design where the designers Shearing of g’ Precipitates in Ni-Base Superalloys in strive to move away from using a uniform (usually the Acta Mater. 59:3484-3497. 35 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic A2: Multiscale phenomena in plasticity 36 Talks Topic A 2: Multiscale phenomena in plasticity Size-Dependent Mechanical Properties of Crystalline Nano- particles Dan Mordehai Department of Mechanical Engineering, Technion, Haifa, Israel It is well established that materials can drastically terial properties, such as the stacking fault energy and change mechanical properties when their size is re- elastic constants. duced to the nanoscale, mainly because of an increase In contrast, Fe nanoparticles (BCC) exhibit a much less in surface to volume ratio and of lowering the amount profound size effect due to strong dislocation pining at of defects in the lattice. In particular, defect-free crys- their nucleation sites. We denote this type of deforma- talline nanostructures reach strengths which are close tion as depinning-controlled mechanisms. Under com- to their ultimate shear strength, since their deforma- pression, the deformation of Fe nanoparticles exhibit tion is controlled by dislocation nucleation from the a size effect, similarily to FCC nanoparticles. However, surfaces. In this talk we examine how the size and they differ in the governing dislocation mechanism. shape of defect-free nanoparticles affect the mechani- While dislocations are nucleated at the vertices of cal response to compression and indentation. both Fe and FCC nanoparticles, these are accumulated Earlier experiments on Au nanoparticles showed that within the Fe nanoparticle instead of escaping from the they become easier to indent as they are smaller, but free surfaces, as in the FCC nanoparticles. a reduction of their size increases their strength under Further more, the size effect is shown to be suppressed compression. With large scale Molecular Dynamics in Ni3Al intermetallic nanocubes under compression, (MD) simulations, we show how the lateral dimensions since the stress concentration vanishes in this geom- give rise to size effect in indentation through the com- etry. An analysis of the dislocation evolution in Ni3Al petition between dislocation storage and depletion on nanoparticles shows that partial dislocations are nu- free surfaces. On the other hand, under compression, cleated at the vertices, shearing the nanoparticle with the size effect arises from a size-dependent dislocation large complex stacking faults planes. nucleation threshold at the nanoparticle’s vertices. A This combined computational-experimental study pro- dislocation nucleation model is employed to study how vides us with insights on how to model dislocation-nu- stress at which FCC nanoparticles yield depends on ma- cleation controlled deformation at the nanoscale. Molecular dynamics study of the response of a nanowire containing defects to a uni-axial strain: case of nickel Kahina Lounis1, El hocine Megchiche1, Zenia Hand 2 1Laboratoire de Physique et Chimie Quantique (LPCQ), Université Mouloud Mammeri, Tizi-Ouzou, Algéria 2Laboratoire de Physique Théorique, Université Abderrahmane Mira, Béjaia, Algéria Nanostructures hold very important potential techno- strain rate on the elastic limit of nickel nanowires, the logical applications nowadays. Besides their reduced role of defects has not yet been explored to our knowl- dimensionality (spatial dimensions) these structures edge. In this work we will present the results of our exhibit peculiar electronic, optical and mechanical simulations of nickel nanowires with defects in them. properties. Recent experiments conducted on nickel The calculations have been carried out using molecu- nanowires have revealed elastic limits many orders of lar dynamics as implemented in the Lammps[4] code, magnitude greater than their corresponding values in where Ni-Ni interactions are modeled by an embedded bulk nickel [1]. This disparity has been attributed to atom model (EAM) kind of semi-empirical potential. differing concentrations of defects (point or extend- Our results show that the elastic limit decreases with ed) present in both systems: nanowire and bulk. To increasing temperature and/or increasing strain rate simulate these systems care must be taken in tuning (frequency). We have found that the elastic limit (yield parameters structure size, temperature, strain/stress strain) decreases by a half when the strain rate (fre- rate, presence of defects to ensure that the simulation quency) varies from 1010 S-1 to 1008 S-1. conditions are as close as possible to the experimental Moreover, we have found that presence of a small setup. Although many researchers [2, 3] have studied cluster of defects (three, six or thirteen monovacan- the influence of the system size, temperature as well as cies) in the nanowire leads to a substantial decrease in 37 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 the elastic limit. Additionally, our results point to the Setoodeh, A, R. Attariani, H & Khosrownejad, M important role played by the initial location, of the de- (2008): Computational Materials Science 44, 378. fect cluster, in the occurrence of the yield point in the Peng, C. Ganesan, Y. Lu, Y & Lou, J. (2012): Journal of nanowire. Applied Physics. 111, 063524. Plimpton, S. (1995): Journal of computational Physics, References 117, 1-19. Celik, E. Guven, I & Madenci, E. (2011): Nanotechnol- ogy 22, 155702. Tension/compression anisotropy in yeild stress and Bauschinger effect in ultrafine-grained metals Tomohito Tsuru1, Yoshiteru Aoyagi2, Yoshiyuki Kaji1, Tomotsugu Shimokawa3 1 Japan Atomic Energy Agency, Tokai-mura, Ibaraki, Japan 2 Tohoku University, Sendai, Miyagi, Japan 3 Kanazawa University, Kanazawa, Ishikawa, Japan While the plastic deformation characteristics of coarse- system seems to occur when some dislocaton sourc- grained metals is generally determined by the aver- es activated. The Bauschinger effect of UFG metals is age quantity of collective motion of dislocations, the caused by the change in dislocation density in the pro- mechanical properties of nanocrystalline metals (d < cess of fowarding and backwarding deformation. Ad- 100 nm, d is the grain size) cannot be simply predict- ditionaly, the yield stresses of tensile and compressive ed based on assumptions of the average quantity of deformation have some sort of plastic anisotropy. UFG collective motion of dislocations. Recently, it has been aluminum shows more significant anisotropy than UFG possible to produce ultrafine-grained metals (100 copper. It would be illustrated well by comparing two nm < d < 1 μm) in bulk by severe plastic deformation materials that the intergranular dislocation nucleation process 1-2) and it has been known these UFG metals plays more important role in tension/compression an- achieve unique and excellent mechanical properties. isotropy. 3-4) As well as this strengthening mechanism, the anom- alous tension/compession deformation characteristics References and the Bauschinger effect have been observed in UFG Y. Iwahashi, Z. Horita, M. Nemoto, J. Wang and T. G. metals 5). Dislocation emission from grain boundaries Langdon (1996): Principle of equal-channel angular becomes more important deformation mechanism to pressing for the processing of ultra-fine grained describe the plastic deformation because it is difficult materials, Scripta Mater. 35: 143-146. to construct any intragranular dislocation source due Y. Saito, H. Utsunomiya, N. Tsuji and T. Sakai (1999): to the very limited individual grain’s space in UFG met- Novel ultra-high straining process for bulk materi- als. However it is difficult to express these unique me- als—development of the accumulative roll-bonding chanical properties in UFG metals using conventional (ARB) process, Acta Mater. 47: 579-583. theories . X. Huang, N. Hansen and N. Tsuji (2006): Hardening In this study, the plastic deromation characteristics by Annealing and Softening by Deformation in Na- of UFG metals were investigated by huge scale atom- nostructured Metals, Science 312: 249-251. istic simulations. Some polycrystalline models with Y. M. Wang and E. Ma (2004): Three strategies to intragulanular Frank-Read sources were constructed achieve uniform tensile deformation in a nanostruc- to elucidate the relationship between the inter- and tured metal, Acta Mater. 52: 1699-1709. intra-granular plastic deformation processes and the M. Haouaoui, I. Karaman and H. J. Maier (2006): Flow mechanical properties. Then the uniaxial tension and stress anisotropy and Bauschinger effect in ultrafine compression were applied to the polycrystalline alumi- grained copper, Acta Mater. 54, 5477-5488. num and copper models. It is found that yield stress J. Rajagopalan, C. Rentenberger, H. P. Karnthaler, G. is strongly influenced by the number of intragranular Dehm and M. T. A. Saif (2010): In situ TEM study of dislocation sources, i.e., dislocation density. Frank- microplasticity and Bauschinger effect in nanocry- Read sources were activated prior to intergranular stalline metals, Acta Mater. 58, 4772-4782. dislocation emission, and the yield event of the whole 38 Talks Topic A 2: Multiscale phenomena in plasticity Particle and solid solution strengthening. Part 1: experiments to control microstructure Philipp Schumacher1,2, Stefan Pogatscher3, Marco J Starink4, Christoph Schick2, Olaf Kessler1, Volker Mohles5, Benjamin Milkereit1,2,4 1University of Rostock, Chair of Materials Science, Rostock, Germany 2University of Rostock, Polymer Physics Group, Rostock, Germany 3ETH Zurich, Department of Materials, Laboratory of Metal Physics and Technology Zurich, Switzerland 4University of Southampton, Engineering Materials Group, Engineering and the Environment, Southampton, UK 5RWTH Aachen, Institute of Physical Metallurgy and Metal Physics, Aachen, Germany During quenching of age-hardenable aluminium alloys cooling than the upper critical cooling rate – is covered. thermal gradients can occur, which generate residual To analyse this wide dynamic range three different stresses and distortion. Heat treatment simulation is a types of DSC devices were utilised. The dependence of powerful tool for the prediction of their extent. How- formation enthalpy on cooling rate and temperature is ever, mechanical properties of the simulated alloy are modelled, providing a consistent physical description required depending on temperature, strain rate and its of precipitated volume fraction and amount of Si re- microstructure, which is strongly affected by the cool- maining in solid solution during cooling. This allows the ing condition. Approaches to model flow curves with generation of well-defined microstructural states with appropriate state variables have therefore been devel- application of controlled heat treatments. Compres- oped in the past, but influences of microstructural ele- sion tests in a quenching and deformation dilatometer ments such as solutes and second-phase particles need were carried out on specific states to investigate the further investigation. This study presents an approach strengthening effect of Si in solid solution and different to generate reliable experimental data on mechanical types of coarse quench-induced precipitates. Thereby, properties of well-defined microstructural states for samples possessing an equal amount of Si in solution the calibration and validation of a simulation model. but different types of precipitates with same precipi- Pure binary Al-Si alloys were analysed as Al-Si is an ideal tate volume fractions were produced and tested. The model system and Si is an important alloying element flow characteristics of these states were compared to in commercial age-harenable 6xxx alloys. During cool- precipitate-free conditions having the same amount of ing from solution annealing of Al-Si alloys two different solute Si. A big advantage of this method is that the types of precipitates occur in certain cooling rate and strengthening contribution of precipitates can be de- temperature ranges. Their microstructure was inves- termined without the need to assume any - potentially tigated by light optical, scanning electron, and trans- inaccurate - superposition law between particle and mission electron microscopy, as well as by atom probe solute strengthening. The fundemental ideas of this tomography. The precipitation enthalpy during cooling technique can be transferred to other precipitation was investigated with advanced DSC techniques in a hardening alloys. The flow behaviour was modelled. wide cooling rate range of 0.0001 K/s to 2 K/s. Hence, The modelling will be presented in part two of this the whole range of physical interest – from slow cool- work. ing close to thermodynamic equilibrium up to faster 39 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Particle and solid solution strengthening. Part 2: modelling plastic behaviour Volker Mohles1, Volker Pankoke1, Philipp Schumacher2, Benjamin Milkereit2 1RWTH Aachen University, Institute of Physical Metallurgy and Metal Physics, Aachen, Germany 2University of Rostock, Chair of Materials Science, Rostock, Germany Through-process modelling (TPM) has been estab- be considered as a work in progress until all new as- lished in recent years to simulate and predict the pects can be validated by corresponding experiments. micro structure and the resulting material properties 4IVM describes the material state by the densities, rx, in the production of aluminium sheet. One core ingre- of four dislocation classes with distinctly different prop- dient of such a simulation set-up is a statistical work erties: mobile dislocations (rmob), dislocation dipoles hardening and recovery model that predicts the evo- (rdip), dislocation locks (rock), and subgrain boundary lution of dislocation densities and the subgrain sizes dislocations (rub). While the mobile dislocations facil- during hot and cold rolling. These quantities affect the itate plasticity, the dipole dislocations do not contrib- material strength and thereby the rolling forces imme- ute to slip even though they can move in response to diately, and they influence texture evolution signifi- internal stress gradients. Lock and subgrain boundary cantly. Furthermore, they are also important in subse- dislocations are considered entirely immobile for now. quent processing because they form the driving force For all dislocation densities rx, generation and anni- for recrystallisation. One such work hardening model hilation rates are defined in dependence of all other that had been integrated in a full TPM set-up is 3IVM+ variables as well as the initial grain size (and eventually (3 Internal Variables Model). As designed, it allows suc- other influences like solute concentrations). By inte- cessful TPM for all rolling and annealing steps in many gration over time, these rates determine the coupled cases. However, 3IVM+ fails to model those annealing evolution of all rx. From these, the work hardening steps well in which only recovery takes place. The main stress is derived by application of the Taylor formula. reason for this lies in the state variables chosen for The total flow stress is calculated as a superposition of modelling. They enforced that during recovery simula- this Taylor stress and models for precipitate and solute tion, the state variables of the model approached the strengthening. same values as for a fully recristallised material, mak- The new model is validated by comparing simulated ing a distinction between recovered and recrystallized flow curves to measured ones. For this, binary Al-Si states impossible. Moreover, only in a few cases 3IVM+ and Al-Mg alloys have been prepared and compression offers good predictions for the impacts of variations tested in varying precipitation states as described. This in alloy composition even though direct strengthen- is described in the accompanying paper titled “Particle ing contributions by particles and by solute atoms had and solid solution strengthening. Part 1: experiments been considered. to control microstructure” by Schumacher, Pogatscher, Therefore, a new statistical work hardening and recov- Starink, Schick, Keßler, Mohles, and Milkereit. Com- ery model called 4IVM has been developed recently. pared to its predecessor, 4IVM offers improved flow Since this model is expected to cover many more as- curve predictions. pects of plasticity than 3IVM+, the new model should 40 Talks Topic A 3: Multiscale phenomena in plasticity Talks Topic A3: Multiscale phenomena in plasticity 41 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Comparison of statistical descriptors for the construction of Statistically Similar RVEs Lisa Scheunemann1, Daniel Balzani2, Dominik Brands1, Jörg Schröder1 1Universität Duisburg-Essen, Institut für Mechanik, Abteilung Bauwissenschaften, Fakultät für Ingenieurwissen- schaften, Essen, Germany 2TU Dresden, Institut für Mechanik und Flächentragwerke, Fakultät für Bauingenieurwesen, Germany In microheterogeneous materials, the effective ma- to ones constructed using probability density functions terial response is influenced by the underlying micro- based on Minkowski functionals to replace the line- structure morphology, the behavior of the individual al-path function. phases and the interaction at the interface. In order to take into account these microstructural effects, ho- References mogenization approaches, such as the FE2-method, see Balzani, D., Schröder, J. & Brands, D. (2009): FE2 simu- e. g. Smit et al. (1998), Miehe et al.(1999) & Schröder lation of microheterogeneous steels based on statis- (2014) are suitable tools. Herein, at every macroscopic tically similar RVEs. Proc. IUTAM Symp. Variational Gauss point, an additional microscopic boundary val- Concepts with application to mechanics of materi- ue problem is solved, which typically incorporates a als, September 22-26, Bochum, Germany. representative volume element (RVE) to represent the Balzani, D., Brands, D. & Schröder, J. (2010): Sensitivity microstructure. As the microstructure of a real mate- analysis of statistical measures fort he reconstruc- rial is governed by a highly complex morphology, the tion of microstructures based on the minimization consideration of such structures involves large compu- of generalized least-square functionals. Tech. Mech. tational efforts which pose a serious drawback to the Vol. 30,297-315. homogenization method. The use of statistically simi- Balzani, D., Scheunemann, L., Brands, D. & Schröder, lar RVEs (SSRVEs) is an alternative which involves much J., (2014): Construction of Two- and Three-Dimen- lower computational costs. SSRVEs have a statistically sional Statistically Similar RVEs for Coupled Mi- similar artificial inclusion morphology as well as a sim- cro-Macro Simulations. Comp. Mech., doi: 10.1007/ ilar mechanical behavior as the real microstructure. s00466-014-1057-6. SSRVEs are constructed by minimizing a least-square Miehe, C., Schröder J. & Schotte, J. (1999): Computa- functional taking into account the difference of statis- tional homogenization analysis in finite plasticity. tical measures computed for the real microstructure Simulation of texture development in polycrystalline and the SSRVE. This approach was proposed by Balzani materials. Comp. Meth. Appl. Mech. Eng., Vol. 171, et al. (2009) for two-dimensional SSRVEs and extend- 387-418. ed to 3D in Balzani et al. (2014). For the construction Schröder, J.: A numerical two-scale homogeni-zation of SSRVEs, the statistical measures used play a crucial scheme: the FE² method. In: Plasticity and Beyond role. Balzani et al. (2010) showed the importance of – Microstructures, Crystal Plasticity and Phase Tran- considering statistical measures of higher order, such sitions, CISM Lecture notes 550, Editors: K. Hackl & as spectral density, Yeong & Torquato (1998) point out J. Schröder, Springer 2014 that hybrid approaches lead to improved results when Schröder-Turk, G.E., Mickel, W., Kapfer, Schaller, S., reconstructing microstructures based on statistical Breidenbach, B., Hug, D. & Mecke, K. (2013): Min- measures. Statistical descriptors based on Minkowski kowski Tensors of Anisotropic Spatial Structures. functionals, a class of integral measures which can be New Journal of Physics. Vol. 15 083028 used to describe geometrical objects, cf. Schröder-Turk Smit, R., Brekelmansm W. & Meijer, H. (1998): Pre- et al. (2013), offer a possibility to increase the efficien- diction of the mechanical behavior of nonlinear cy of construction compared with the lineal-path func- heterogeneous systems by multi-level finite element tion. This contribution focusses on the comparison of modeling. Comp. Meth. Appl. Mech. and Eng., Vol. SSRVEs obtained from different sets of statistical meas- 155, 181-192. ures. Namely, SSRVEs based on volume fraction, spec- Yeong, C.L.Y. & Torquato, S. (1998): Reconstructing tral density and lineal-path function will be compared random media. Phys. Rev. E., Vol. 57, 495-506. 42 Talks Topic A 3: Multiscale phenomena in plasticity Phase transitions’ energies and activation energies from nothing else than indentation loading curves Gerd Kaupp University of Oldenburg, Faculty 5 Natural Sciences, Oldenburg, Germany Pyramidal and conical (as do spherical) indentation loading ranges. Examples with Berkovich pyramid are loading curves strictly follow the FN = k h 3/2 law for all compared for different types of materials. uniform materials under all thinkable conditions of The precision of the new analytic technique without constant normal force increase. This has been shown approximations and without iterations allows also for by analysis of experimental loading curves from all over the determination of the activation energy of phase the world, giving linear correlation coefficients of r > transitions by indentations at variable temperatures. 0.999 and often r > 0.9999. It does not matter whether These are available with reliable temperature control the materials are elastic, plastic, hard, ductile, brittle, by various commercial nanoindentation instruments. viscous, adhesive, soft, etc. Undeniable surface effects But activation energy for pressure induced phase are revealed and directly corrected. The penetration transformations is unprecedented in materials re- resistance k has the dimension [N/m3/2]. Elementary search. Its measurement under the Berkovich pyramid mathematics derives the applied work (Wapplied) and will be exemplified with the phase transition of NaCl the indentation work (Windent) relating with 5 : 4 for all (001), where the B1 and B2 states are most precisely uniform materials. The FN = k h 3/2 parabola enables the known, and where the transition is used as a pressure simplest determination of the indentation work that standard. The k1 and k2 values change with indenta- is precisely 80% of the applied work. The remaining tion temperature, here from room temperature to 20% produce all long range processes away from the 400°C, with correlation coefficients of r > 0.9999. The indentation volume, be these reversible or irreversible, normalized transition work (Wtrans/mN) rises with tem- including local phase transitions, if they occur. perature, due to deeper immersion h. The semi-loga- This quantitative analysis of indentations is of impor- rithmic plot of Wtrans/mN against temperature is linear tance for the identification and energetic of pressure and the slope provides the normalized phase transi- induced phase transitions (Wtrans). When these occur tion activation energy (Ea/mN) for the calculation of the F -h3/2N -plot yields a linear branch before (slope k1) the transition work for all interesting temperatures and and after the onset of the phase transition (slope k2) pressures. Ea/mN proves insensitive to creep-on-load. with sharp intersection at a kink point, both with the It yields valuable new material’s property of practical above correlation coefficients. Clearly, the transformed importance for adjustments of compatibility within material exhibits different mechanical properties in- composite materials under mechanical impact, or for cluding the penetration resistance k. This is observed the interpretation of shearing interactions at elevated for structural transitions and all other types of phase temperatures, etc. transformation, simply by the energy balance: Wtrans = full Wapplied – (W1applied + W2applied). Phase transforma- References tion energies can thus be positive (endothermic) or Kaupp, G. (2014): Activation energy of the low-load negative (exothermic). Basic arithmetic using the FN = NaCl transition from nanoindentation loading curves k h3/2 law allows for their calculation at freely chosen – Scanning, DOI: 10.1002/sca.21158; 8 pages; Wiley. 43 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Rate effects in finite element modeling of transformation in- duced visco-plasticity Maher El Haj Kacem1, Fabrice Barbe1, Nicolas Lecoq1,2 1INSA de Rouen, Groupe de Physique des Matériaux, Saint Etienne du Rouvray, France 2Université de Rouen, Morphodynamique Continentale et Côtière, Mont-Saint-Aignan, France The TRansformation Induced Plasticity (TRIP) in steels guish between creep deformation and transformation is a permanent strain which is achieved under the com- plasticity. bination of a phase transformation at elevated tem- It is found that not only viscosity can be very influen- perature and small external loading. This phenomenon tial on the prediction of the transformation induced can be interpreted from the elastoplastic interactions plasticity, but also the final properties of the product that occur locally between the growing particles and phase could be considerably affected due to the phase a parent matrix and which preferentially develop in transformation history. The FE Modelling is also used the loading direction. This model mechanism enables for other objectives: (i) to evaluate the contribution to obtain a first-order agreement on TRIP, as shown by of viscosity to predict Transformation visco-plasticity the model of [Leblond, 89] or by numerical simulations at different strain-rate sensitivities and (ii) to analyse [Tahimi et al., 2012] for displacive as well as diffusive particular cases of model TRIP tests which could help transformations. improving a simple rate-sensitive analytical model. However, in most modelling approaches (e.g. Leb- lond, Taleb-Sidoroff, Fischer et al. ; see [Barbe & Quey, References 2011] for references), viscous strains are neglected. By [Leblond, 89] Leblond, J.B., Mathematical modelling contrast, on an experimental basis, for 100C6 steel at of transformation plasticity in steels II: coupling 700°C, both phases show high strain-rate sensitivity with strain hardening phenomena Int J Plasticity [Tahimi et al., 2012]. The analytical model presented 5:573–591, 1989. in [Vincent et al., 2003] is one of the few accounting [Tahimi et al., 2012] A. Tahimi, F. Barbe, L. Taleb, R. for viscous effects but relies on strong hypotheses con- Quey, A. Guillet, Evaluation of microstructure-based cerning the distribution of plasticity between phases. transformation plasticity models from experiments In this work, the problem of viscoplastic interactions on 100C6 steel. Comput Mater Sci 52:55–60, 2012. between diffusively growing phases is introduced ex- [Barbe & Quey, 2011] F. Barbe, R. Quey. International plicitly in the constitutive laws of a phase transforming Journal of Plasticity. 27 (2011) 823-840. RVE; the mechanical problem is solved by means of the [Vincent et al., 2003] Yannick Vincent, Jean-Michel finite element method [Tahimi et al, 2012, Barbe and Bergheau, Jean-Batiste Leblond. Viscoplastic behav- Quey, 2011]. A particular processing of the total ine- iour of steels during phase transformations. C.R. lastic deformation induced during a classical TRIP test Mecanique 331(2003) 587-594. (consisting in imposing a small constant stress imposed during the phase transformation) enables to distin- 44 Talks Topic A 4: Multiscale phenomena in plasticity Talks Topic A4: Multiscale phenomena in plasticity 45 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Size effects in void growth from nano- to microscale Javier Segurado1,2, Hyung-Jun Chang1, Javier LLorca1,2 1 Department of Materials Science, Polytechnic University of Madrid, Spain 2Madrid Institute for Advanced Studies of Materials (IMDEA Materials Institute), Spain The ductility of metallic materials is determined to to nucleate the dislocations were in the order of GPa, large extent by the kinetics of void growth. The growth much larger than typical yield of these materials. mechanisms depend on the size of the initial voids. In For micron sized voids, DDD simulations were the case of very small voids (<100 nm), void growth is performed. In this case both 2D models representing triggered by the emission of shear dislocation loops cylindrical holes [2,3] and 3D models [4] with from the void surface when the stress approaches spherical voids were employed. The interaction of the strength of the perfect crystal. For voids with the dislocations with the void surface was accounted sizes >1 μm, void growth is controlled by dislocations coupling the DDD simulations with finite element nucleated in the bulk, that shear the void upon slip. models using the Needleman and Van-der-Giessen For a correct description of nano-sized void growth, approach. the discrete nature of the crystal has to be accounted This study using different models and covering a void to accurately represent the nucleation process [1]. size range of several orders of magnitude allow to have However, for micron-sized voids the volume of material a general picture of the mechanisms at each scale and and the number of dislocations involved prevents the the size effects in void growth process. use of a pure discrete study. In this case, Discrete Dislocation Dynamics (DDD) arises as an ideal technique References because it allows the use of larger simulation volumes [1] H-J. Chang, J. Segurado, O. Rodríguez de la Fuente, by considering a continuum framework with an explicit B. M. Pabón , J. Llorca (2013), “Molecular dynam- representation of the individual dislocations and ics modeling and simulation of void growth in two their interactions. Moreover, size effects are naturally dimensions” Modelling Simulation in Materials Sci- reproduced by DDD simulations [2-3] ence and Engineering 21 075010 In this work, simulation of the void growth process [2] J. Segurado , J. Llorca (2010) Discrete dislocation at different length scales (from 1 nm to microns) will dynamics analysis of the effect of lattice orientation be presented for an ideal FCC material with special on void growth in single crystals. International Jour- emphasis on void size effects. nal of Plasticity 26, 806-819, At the nano-scale, the void growth process has been [3] J. Segurado, J. Llorca, (2009) An analysis of the studied first by means of a 2D model of a periodic array size effect on void growth in single crystals using of circular voids [1]. The simplicity of the model allowed discrete dislocation dynamics Acta Materialia, 57, to cover a wide range of void sizes (<0.1microns). 1427-1436 In addition, 3D models with cilindrical holes were [4] H-J Chang, J. Segurado, J. LLorca (2015), Three-di- used at smaller sizes to confirm the similarity of the mensional dislocation dynamics analysis of size ef- mechanisms in the two cases : dislocation nucleation fects on void growth, Scripta Materialia 95,1-14 at the void surface. The level of stresses necessary Dislocation interaction across grain boundaries and grain boundary yielding in a discrete dislocation dynamics frame- work Markus Stricker, Daniel Weygand Institute for Applied Materials IAM, Karlsruhe Institute of Technology, Germany The plasticity of polycrystalline samples is strongly re- a residual Burgers vector¹. Recent strain gradient plas- lated to the effective resistance of grain boundaries ticity models describe this process phenomenological- (GBs) against plastic flow. Depending on the crystallo- ly², but the underlying physical picture is unclear. This graphic misorientaion of adjacent grains, a dislocation work revisites GB yielding from a DDD point of view, fo- from one grain is either blocked by the GB, transmitted cusing on the elastic interaction of discrete dislocations completely into the next grain or transmitted leaving across GBs modelled as impenetrable for dislocations 46 Talks Topic A 4: Multiscale phenomena in plasticity and adresses the question how the effective resist- the mismatch between otherwise cancelling stress and ance to plastic slip of a GB can be quantified within this displacement fields of dislocations in the vicinity of the framework. A systematic study of bicrystalline samples GB. This work discusses the (continuum) definition of containing tilt GBs is done, where the misorientation GB yielding and shows insights from DDD to bridge the between the grains is varied between 0° to 45°. A sim- gap between molecular dynamics findings4 to continu- ple shear loading is applied and the strain profiles per- um level frameworks. pendicular to the GB and the strain gradients at the GB are evaluated: Although the GBs are physically impen- References etrable for dislocations within this framework3, yield- [1] Sutton, A. P. & Balluffi, R. W. (1996): Interfaces in ing of the GB is observed due to transparency of the crystalline materials, Clarendon Press GB to the corresponding stress and strain fields. The [2] Zhang, X. et al. (2014): J. Mater. Res., 29: 2116 results show that with an increasing misorientation [3] Weygand, D. et al (2002): Model. Simul. Mater. Sc., angle, the effective transmission of plastic slip across 10:437 a GB decreases due to the effective residual Burgers [4] Jin, Z.-H. et al. (2006): Scripta Mater., 54:1163 vector left at the GB and the strain gradients reflect Dislocation alignment tensors: their conservation laws and how to determine them from discrete dislocation configura- tions Thomas Hochrainer Universität Bremen, BIME, Germany Alignment tensors are well known measures for the be obtained from DD simulations or from TEM pictures characterization of directional distributions of line like of dislocations. In light of these discrete definitions we structures. They have recently been introduced to dis- also review the evolution equations of the alignment location theory (Hochrainer 2015). The series of align- tensors, as introduced in Hochrainer 2015, and clarify ment tensors of increasing order recovers the total their interpretation as conservation laws. dislocation density as zeroth order tensor and the dis- location density tensor is connected to the alignment References tensor of first order. The second order dislocation den- Hochrainer, T. (2015): Multipole expansion of contin- sity tensor is a tensorial generalization of the occasion- uum dislocation dynamics in terms of alignment ally used decomposition of the total dislocation dnesity tensors, ArXiv e-prints. in edge and screw character (e.g., Reuber et al. 2014). Reuber, C., Eisenlohr, P., Roters, F., Raabe, D., 2014. Besides the dislocation alignment tensors we also in- Dislocation density distribution around an indent in troduce density measures of dislocation curvature, the single-crystalline nickel: Comparing nonlocal crystal scalar measure of which is closely related to the num- plasticity finite-element predictions with experi- ber of dislocations. In the current talk we show how ments. Acta Materialia 71 (0), 333-348 the alignment tensors and the curvature tensors may Representation of Dislocation Interactions in a Dislocation Density Field Theory for Crystal Plasticity Severin Schmitt1, Peter Gumbsch1,2, Katrin Schulz1 1Institute of Applied Materials, Karlsruhe Institute of Technology, Germany 2Fraunhofer Institute for Mechanics of Materials, Freiburg, Germany Even though many phenomenological models have a drive to derive models containing physically moti- been developed for the description of dislocation vated formulations. Multiscale material modeling is based plasticity incorporating the underlying effects inevitable to bring the effect of length and time scales due to the internal length scale, there has always been of smaller scales to regimes where they are relevant 47 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 for the prediction of macroscopic material properties. fects of the discrete scale, we derive a formulation of Multiscale material modeling aims to either couple the the internal stress caused by plastic distortion due to simulation of different scales at the prize of high com- dislocation motion and the interaction of dislocations putational costs or to reduce the number of unknowns on a slip system. of a system by incorporating information about the We discuss the method for the computation of the physical behavior gained on small scales onto larger internal stresses derived for a 2d dislocation configu- scales. The latter approach presumes a deep under- ration and compare our results with discrete disloca- standing of the underlying physical effects and the tion dynamics and results from statistical physics [3]. application of homogenization techniques to translate Furthermore we demonstrate how these results can discrete phenomena to a continuous representations. be generalized and applied to a 3d dislocation density In recent years, different approaches for physically field theory. based continuum theories have been introduced. Al- lowing for different dislocation orientations, the Con- References tinuum Dislocation Dynamics Theory was formulated [1] Hochrainer et al., Continuum dislocation dynamics: in order to introduce a kinematic description of the Towards a physical theory of crystal plasticity. JMPS, evolution of dislocations displayed in a density field 63:167-178,2014. theory [1]. Based on this theory, we focus on devel- [2] Schulz et al., Analysis of dislocation pile-ups using oping methods for incorporating the physical behavior a dislocation-based continuum theory. MSMSE, of dislocations and their stress interactions into the 22:025008, 2014. dislocation density field theory. The understanding of [3] Groma et al., Spatial correlations and higher-order these processes is gained on the scale of discrete dis- gradient terms in a continuum description of dis- location dynamics and analytical descriptions available location dynamics. Acta Materialia, 51:1271-1281, for simplified 2d systems [2]. By homogenizing the ef- 2003. 48 Talks Topic A 4: Multiscale phenomena in plasticity Microstructural comparison of continuum models for dislo- cation plasticity Mehran Monavari, Michael Zaiser, Stefan Sandfeld Friedrich-Alexander-Universität Erlangen-Nürnberg, Fürth, Germany Continuum modeling of dislocation microstructures CDD models, CDD(1) and CDD(2) [7]. We then discuss in started with the early works of Kröner and Nye [1]. detail the advantages and the deficiencies of the two They envisaged the geometrically necessary disloca- CDD variants in comparison with the initially men- tion (GND) density tensor (α) as the curl of the plastic tioned models of Acharya, Groma and Arsenlis. As a distortion in the crystal. The Kröner-Nye tensor, how- benchmark test we compare the performance of these ever, cannot represent the statistically stored disloca- models by studying the evolution of dislocation micro- tions (SSD) which become relevant when the plastic structure in a velocity field which idealizes the situa- distortion is resolved on a larger scale than the scale tion found in persistent slip bands (PSB). This is a very of single dislocations. Various continuum dislocation challenging model system because a continuum theory models have approached this problem from different needs to be able to represent the formation of edge perspectives: (I) complementing the evolution equa- dipoles in regions of low velocity and the threading tion of α by semi- phenomenological terms (A. Achar- screw dislocations in the channels – a complex interac- ya [2]); (II) representing fluxes of positive and negative tion of two types of SSDs and their (partial) conversion edge dislocations which automatically can represent into GND fields all of which has been directly observed GNDs and SSDs and their mutual conversion (I. Gro- in experiments. ma [3]); generalizing this approach one step further by distinguishing edge and screw dislocations forming References systems of rectangular loops as done by A. Arsenlis [4]. [1] E. Kröner, Springer-Verlag, 1958. Recently, also theory that allows for arbitrary disloca- [2] A. Acharya, J. Mech. and Phys. Solids 52 (2) tion orientations was proposed in the form of the high- (2004)301–316. er-dimensional continuum dislocation dynamics theory [3] I. Groma, Phys. Rev. B 56 (10) (1997) (hdCDD) introduced by T. Hochrainer [5]. Subsequent- [4] A. Arsenlis, et al., J. Mech. and Phys. Solids 52 (6) ly, Hochrainer et al. derived a systematic framework (2004) for constructing numerically efficient models based on [5] T. Hochrainer, et al., J. Mech. and Phys. Solids 63 Fourier expansions of the hdCDD density tensor [5,6] (2014 which, however, require closure assumptions in order [6] T. Hochrainer, submited to Phil. Mag. (arXiv: to arrive at finite systems of continuum dislocation dy- 1409.8461) namics (CDD) equations. [7] M. Monavari, et al., Mater. Res. Soc. Symp. Proc. In this paper we use the maximum entropy principle 1651 (2014) to derive closure assumptions for the two lowest order 49 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic A5: Multiscale phenomena in plasticity 50 Talks Topic A 5: Multiscale phenomena in plasticity The «Cauchystat»: accurate control of the true stress in mo- lecular dynamics simulations of martensitic phase transfor- mations Ronald E. Miller1, Ellad B. Tadmor2, Noam Bernstein3, Fabio Pavia4, Josh Gibson1 1Carleton University, Ottawa, Canada 2University of Minnesota, St. Paul, MN, USA 3NRL, Washington, DC, USA 4EPFL, Lausanne, Switzerland When using molecular dynamics (MD) to study, for ex- to the system. The “Cauchystat” is based on the con- ample, soft materials or stress-induced phase transfor- stant stress ensemble presented by Tadmor and Mill- mations of crystals, we are confronted with the need to er (2011), but with modified equations of motion that describe the material behaviour from the perspective update the system boundary conditions in response of finite deformation mechanics. Perhaps the most to the resulting deformation of the simulation cell. As important consequence of this is the correct definition a clear example of the method’s usefulness, we show and interpretation of what we nominally refer to as the that the correct stress control is important in the case “stress” on a system. of martensitic phase transformations, where the pre- It is common in MD simulations to want to control the dicted martensitic start temperature and austenitic fin- applied stress. In some MD codes, this control is limit- ish temperature are significantly altered as compared ed to control of only the hydrostatic pressure, or only to the Parrinello-Rahman result. We also examine the the direct (axial) stresses. In order to control the full effects of shear stress on the mechanism of the phase stress tensor including shear stress, MD codes almost transformation. universally use the Parrinello-Rahman technique (Par- rinello & Rahman 1981) or some related variation (e.g. References Martyna et al. 1994, Wentzcovitch 1991). However, Parrinello, M. and A. Rahman (1981): Polymorphic none of the these techniques are able to control the transitions in single crystals: A new molecular dy- true (Cauchy) stress applied to the system. Instead, namics method. J. Appl. Phys., 52(12):7182–7190. they apply an approximation to the second Piola-Kirch- Martyna, G.L., D.J. Tobias and M.L. Klein (1994): Con- hoff stress (related to the “engineering” stress). The stant-pressure molecular dynamics algorithms. J. true Cauchy stress that results during such a simula- Chem. Phys., 101(5) pp. 4177-4189. tion is dependent on the deformation of the simulation Wentzcovitch, R.M. (1991): Invariant molecular-dy- cell, and it cannot be known a priori. In fact, it can be namics approach to structural phase transitions. significantly different from the nominally applied stress Phys. Rev. B, 44(5):2358–2361. when the deformation is large. Tadmor, E.B. and R.E. Miller (2011): Modeling Mate- In this presentation, I will discuss an alternative MD rials: Continuum, Atomistic and Multiscale Tech- algorithm that controls the true Cauchy stress applied niques. Cambridge: Cambridge University Press. Multiscale modeling of solute atom effect on critical re- solved shear stress of Fe Masato Wakeda1, Shigenobu Ogata1,2 1Osaka University, Japan 2Kyoto University, Japan Solute atom changes mechanical properties of bcc Fe; on screw dislocation is a key to design and control plas- critical resolved shear stress (CRSS) and work harden- tic properties of Fe alloys. In this study, we predict CRSS ing coefficient increase with increasing solute atom of Fe-Si alloys using a multiscale modelling framework, concentration at room temperature [1]. In bcc Fe al- which includes from density functional theories (DFT) loys, screw dislocation is a dominant plastic deforma- calculation of atomistic scale to kinetic Monte Carlo tion unit, since the energy barrier for screw dislocation model for screw dislocation dynamics. motion is much higher than that of edge dislocation. First we investigated the interaction between solute Therefore, understanding of the effect of solute atom Si and screw dislocation in bcc Fe using DFT calcula- 51 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 tion method [2]. In the calculation models, of which location motion. The kinetic Mote Carl model can eval- crystal structure is bcc Fe, there are substitutional Si uate the screw dislocation dynamics with considering atoms and two screw dislocations with opposite helici- kink nucleation and migration and cross-kink mecha- ties. It is found that the substitutional Si atoms change nism. Based on the obtained screw dislocation velocity, the stable screw dislocation core structure, which is a we evaluated CRSS using a relationship between plastic six-fold symmetry in the case of pure Fe [3]. Moreover, strain rate and dislocation velocity, so called Orowan’s interaction between screw dislocation and solute Si is equation. The CRSS of Fe-Si alloys is smaller than that found to be attractive, and the interaction becomes of pure Fe at low temperature because of the reduc- larger if the screw dislocation approaches to the sol- tion of energy barrier for kink nucleation due to solute ute Si. Based on charge density distribution, we show Si. In contrast CRSS of Fe-Si alloys is larger than that of origin of the interaction from an electronic viewpoint. Pure Fe at high temperature because of the increase Using empirical Fe-Fe [4] and Fe-Si [5] interatomic po- of energy barrier for kink migration due to solute Si. tentials, which can quantitatively reproduce attractive These results agree well with experimental reports of interaction between solute Si and screw dislocation, Fe-Si alloys, where solute softening at low temperature we next evaluated the energy barriers for screw dis- and solute strengthening at high temperature are ob- location motion. In this calculation, we use a larger served. scale atomic model with more than 100,000 atoms, and there is one screw dislocation in the model. The References energy barriers for screw dislocation motion via kink [1] Advanced Steels: The Recent Scenario in Steel mechanism are evaluated for a pure Fe model and Fe- Science and Technology, Y. Weng, H. Dong, Y. Gan. Si alloy models. It is observed that energy barrier for Springer, Berlin (2011) pp.229-240. kink nucleation decreases if the screw dislocation ap- [2] http://www.openmx-square.org/ proaches to solute Si, while increases if the screw dislo- [3] M. Itakura, H. Kaburaki, M. Yamaguchi, Acta Ma- cation moves away from solute Si because of attractive ter., 60 (2012) pp.3698-3710. interaction between solute Si and screw dislocation. [4] G. J. Ackland, M. I. Mendelev, D. J. Srolovitz, S. Han Moreover, it is found that solute Si increases energy and A. V. Barashev, J. Phys.: Condens. Matter., 16 barrier for kink migration. (2004) pp. S2629-S2642. We finally evaluated the CRSS at give temperature, Si [5] M. Wakeda, H. Kimizuka and S. Ogata, J. Japan Inst. concentration and strain rate using the calculated en- Met. Mater., 77 (2013) pp. 409-414. ergy barriers and kinetic Mote Carl model for screw dis- Multi-scale modeling of dislocation-precipitate interactions in Fe: from molecular dynamics to discrete dislocations A. Lehtinen,1 F. Granberg,2 L. Laurson,1 K. Nordlund,2 M. Alava1 1Department of Applied Physics, Aalto University School of Science, Aalto, Espoo, Finland 2Department of Physics, University of Helsinki, Finland Plasticity in crystalline materials is due to the motion cipitate potential and the dislocation mobility are ob- of crystal defects known as dislocations. Dislocations tained from a molecular dynamics simulations. When create an anisotropic stress field around themselves dislocation encounters an impenetrable obstacle, eg. which can be quite complex, giving rise to a rich varie- precipitate, it will become pinned. If the external stress ty of possible interactions. Discrete Dislocation Dynam- is high enough, the dislocation bypasses the obstacle ics (DDD) is a method where the dislocation lines are by bending around it, leaving behind an Orowan loop. taken to consist of straight segments. The dislocation New dislocations need more stress to get depinned be- stress fields are obtained from linear elasticity theory. cause they must overcome the old loop in addition to Reactions related to the dislocation core, such as junc- the obstacle. This leads to work hardening of the metal tion formation and pinning to defects, are beyond the which is an important phenomenon to understand eg. reach of linear elasticity theory and thus require input in the context of building structural parts for nuclear from more microscopic approaches. reactors. Here we combine molecular dynamics (MD) with DDD in order to model carbide precipitate interactions with References edge dislocations in BCC-iron. We have implemented Athanasios Arsenlis et al. (2007): Enabling strain immobile spherical precipitates into the ParaDis[1] si- hardening simulations with dislocation dynamics. mulation code, interacting with the dislocations via a Modelling and Simulation in Materials Science and Gaussian potential which generates a normal force to Engineering. the dislocation segments. The parameters for the pre- 52 Talks Topic A 5: Multiscale phenomena in plasticity Detailed description of the screw dislocation motion in iron revealed by atomistic simulations Ghiath Monnet1, Akiyoshi Nomoto2 1 EDF – R&D, MMC, Moret sur Loins, France 2 CRIEPI, Tokyo, Japan It is well known that the motion of screw dislocations Then, simulation results are stochastically analyzed fol- is the key feature of plastic deformation in body-cen- lowing a recently reported theory [Monnet 2011]. The tered-cubic materials at low temperature. In spite of analysis results allow for the determination of parame- the large number of associated investigations reported ters of thermal activation, such as the activation ener- in the literature, some important issues are still un- gy and volume. The identification of these parameters clear. allows for the establishment of constitutive equations, One of the most important of these issues is the abili- necessary for the description of the dislocation mobili- ty of screw and other dislocations to move on specific ty over the different slip planes at the continuum scale. crystallographic planes, which determines their availa- bility as active slip planes. References In this work, we first present new molecular dynamics Monnet, G., 2011. Determination of the activation en- results of dislocation motion in iron. Simulations con- ergy by stochastic analyses of molecular dynamics sim- ditions were varied in order to cover a large spectrum ulations of dislocation processes. Philosophical Maga- of factors affecting the dislocation motion, such as the zine, 91(29), pp.3810–3829. dislocation length, temperature, strain rate and the state of the applied stress. Depinning-Controlled Plastic Deformation during Nanoin- dentation of BCC Iron Thin Films and Nanoparticles Roman Kositski, Dan Mordehai Department of Mechanical Engineering, Technion – Israel Institute of Technology, Haifa, Israel The strength of a dislocation-free specimen at the on the periphery of the indenter. The dislocations are sub-micrometer scale focuses great attention in recent nucleated on six possible slip systems: 4 in-plane and years. One of the techniques commonly employed to 2 out-of-plane directions. However, as opposed to FCC study mechanical properties at this scale is nanoin- metals, the dislocations remain pinned after nucleation dentation. Nanoindentation of Au (FCC structure) na- on both ends to the contact area with the indenter. A noparticles revealed that the indentation forces de- drop in the load, which in turn corresponds to strain crease as the particle size increases and that thin-films bursts, is observed only when these dislocations depin of the same height are substantially harder [1]. Based from around the indent and not with the nucleation on Molecular Dynamics (MD) simulations, it was sug- of a new dislocation [2]. Thus, we denote this type of gested that the deformation commences with disloca- deformation as depinning-controlled. tion nucleation and that the size effect arises from the Two depinning mechanisms are identified in thin films. competition between accumulating the nucleated dis- The out-of-plane dislocations detaches from the indent locations and the efficiency of depleting them on the by turning into prismatic loops via double cross-slip lateral surfaces. and annihilation of their screw components. The in- In this work we present MD simulations of nanoin- plane dislocations, which are half prismatic loops, de- dentation α-Fe (BCC phase) thin films and nanoparti- pin from their nucleation site on both ends and glided cles in order to better understand how dimensionali- away from the indenter. ty effect their mechanical response and the effect of Indentation of faceted nanoparticles demonstrates size on the strength of BCC samples. After an elastic similar dislocation mechanism. In addition to the regime, which corresponded well to a Hertzian curve, mechanisms found in thin-films, the in-plane disloca- plastic deformation was accompanied with small load tions depin only on one end at a time, resulting in pure drops. A detailed analysis revealed that ½<111>(110) screw dislocation that reaches the lateral surfaces. edge dislocations are nucleated beneath the top facet Glide of these screw dislocations to upper facets pro- 53 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 vides an additional route for dislocations to escape the References crystal, as well as depinning of the second end. Mordehai, D., Kazakevich, M., Srolovitz, D. J., & Due to the locality of the depinning-controlled defor- Rabkin, E. (2011). Nanoindentation size effect in mation, an indentation size effect was not identified in single-crystal nanoparticles and thin films: A com- the simulations, nor was a difference found between parative experimental and simulation study. Acta thin films and nanoparticles of the same height, in Materialia, 59(6), 2309-2321. contrast with the observations in FCC metals. Finally, Li, J., Van Vliet, K. J., Zhu, T., Yip, S., & Suresh, S. we relate the dislocation mechanisms during the de- (2002). Atomistic mechanisms governing elastic pinning-controlled deformation to the frequency and limit and incipient plasticity in crystals. Nature, extent of strain bursts during nanoindentation of BCC 418(6895), 307-310. specimens. 54 Talks Topic A 6: Multiscale phenomena in plasticity Talks Topic A6: Multiscale phenomena in plasticity 55 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Gradient enhanced modeling of fcc and bcc nanocrystalline materials Benjamin Klusemann1, Swantje Bargmann1,2, Yuri Estrin3 1Institute of Continuum Mechanics and Materials Mechanics, Hamburg University of Technology, Germany 2Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Germany 3Centre for Advanced Hybrid Materials, Monash University, Clayton, Australia Nanocrystalline materials are polycrystalline materials By contrast, nanocrystalline body-centered cubic (bcc) with an average grain size below 100 nm. Their me- materials show a decrease of the strain rate sensitivity chanical properties are distinctly different from those with decreasing grain size. To account for experimen- of coarse grained materials. Therefore, bulk nanocrys- tal observations for bcc materials, we have modified talline materials have received great attention of the the original phase-mixture model to capture this in- materials research community. verese strain rate dependency. We assume that plastic A modeling approach for nanocrystalline materials deformation in bcc materials is governed by the Peierls adopted here is based on the phase-mixture model in- mechanism, while the constraints put on the disloca- troduced by Kim et al. (2000a). In this model, different tion kink formation by the small grain size are consid- deformation mechanisms are assumed to operate in ered to be responsible for a decrease of the strain rate the grain interior and the grain boundaries. It is fur- sensitivity with grain refinement. The model for dislo- ther assumed that the strain and the strain rate are the cation glide is modified accordingly. same in both phases. For simplicity, the nanocrystal- Additionally, we look into the effect of strain gradients line grain shape is approximated as cube-shaped. The on the mechanical response of nanocrystalline materi- stress is determined additively by a rule of mixtures. als. The phase mixture model is augmented with gra- The deformation mechanism in the grain bounda- dient terms. Differences in the mechanical behavior of ries is associated with the diffusional mass transport fcc and bcc nanomaterials will be discussed in terms of along the boundaries; the maximum stress that can be the numerical results obtained with this gradient en- supported by the boundary phase is set to be equal hanced model. to the yield strength of the amorphous state (Kim et al., 2000b). As the model should be valid over several References length scales, from coarse grained material to nanom- Kim, H. & Estrin, Y. & Bush, M. (2000a): Plastic defor- eter grain sizes, Kim et al. (2000a) considered in the mation behaviour of fine-grained materials. Acta grain interior dislocation glide mechanism as well as Materialia, 48 (2), 493 - 504. diffusion mechanisms, namely Nabarro-Herring creep Kim, H. S. & Bush, M. B. & Estrin, Y. (2000b): A phase and Coble creep. The studies by Kim and Estrin (Kim mixture model of a particle reinforced composite and Estrin, 2005, 2008) showed that the model is ca- with fine microstructure. Materials Science and pable of correctly predicting the transition of the flow Engineering: A, 276 (12), 175 - 185. stress from the Hall-Petch behavior in the conventional Kim, H. S. & Estrin, Y. (2005): Phase mixture modeling grain size range to an inverse Hall-Petch relation for na- of the strain rate dependent mechanical behavior nocrystalline materials. Especially for small grain size of nanostructured materials. Acta Materialia, 53 (3), and low strain rates, the material behavior is controlled 765 - 772. by diffusion mechanisms. Additionally, their studies Kim, H. S. & Estrin, Y. (2008): Strength and strain hard- showed an increase of the strain rate sensitivity with ening of nanocrystalline materials. Materials Sci- decreasing grain size. However, this type of behavior ence and Engineering: A, 483-484 (0), 127 - 130. is only observed in face-centered cubic (fcc) materials. 56 Talks Topic A 6: Multiscale phenomena in plasticity A consistent homogenization theory for a higher order plas- ticity model from meso to macro scale Phan Van Tung, Poh Leong Hien National University of Singapore, Singapore Classical plasticity models, being scale independent, Considering an idealized bending problem, we illus- cannot capture any size depedent behavior. A remedy trate the excellent match between the homogenized is to adopt a gradient plasticity model at the sub-granu- solutions and meso solutions for the two limiting cas- lar (meso) scale to account for the different micro-pro- es – microfree and microhard conditions at the grain cesses leading to the various size effects. In this contri- boundaries. It is also highlighted that through the ho- bution, we adopt, at the meso scale, an isotropic gradi- mogenization framework, the strain gradient plasticity ent plasticity model (Gurtin, 2004) which incorporated model at the meso scale translates into a micromorphic the plasticity rotation effect to mimic the behavior of continuum at the macro scale. an analogous crystal plasticity model with multiple slip The homogenized plasticity model is next implement- systems (Bardella and Giacomini, 2008). ed numerically, and its predictive capabilities further- For a generic problem, the interaction and competition more demonstrated through a plane indentation prob- between the different processes are captured through lem. For the aforementioned two limiting cases, the three length scale parameters: a microstructural length homogenized solutions resemble closely the reference scale characterizing the rapid intra-granular fluctua- meso solutions, both in terms of the load displacement tions, the grain size describing the direct grain bound- graphs and the plastic strain profiles. It is noteworthy ary effect, and a structural length scale accounting for that the excellent predictions are obtained with a sig- the overall structural effect (Poh et al., 2013). Such a nificantly lower computational cost. high resolution approach, however, is computationally expensive for a large problem since the FE discretiza- References tion has to be done at a sub-granular level. Gurtin, M.E. (2004): A gradient theory of small-defor- This motivates a novel homogenization theory (Poh, mation isotropic plasticity that accounts for the 2013) that translates the isotropic plasticity model Burgers vector and for dissipation due to plastic spin from meso to macro. First, we introduce an additional – Journal of the Mechancis and Physics of Solids, 52: kinematic field that characterizes the average surface 2545-2568. deformation of a unit grain. Next the Hill-Mandel con- Bardella, L. & Giacomini, A. (2008): Influence of ma- dition is applied to extract the homogenized govern- terial parameters and crystallography on the size ing equations at the macro scale. Departing from most effects describable by means of strain gradient homogenization approaches, we furthermore impose plasticity – Journal of the Mechanics and Physics of the equivalence of energy and dissipation across the Solids, 56: 2906-2934. two scales in order to determine the macroscop- Poh, L.H., Peerlings, R.H.J, Geers, M.G.D. & Swad- ic constitutive relations and plasticity flow rules. The diwudhipong, S. (2013): Towards a homogenized scale translation framework is thus thermodynamical- plasticity theory which predicts structural and mi- ly consistent, with the three length scale parameters crostructural size effects – Journal of the Mechanics – the microstructural length scale, the grain size and and Physics of Solids, 61: 2240-2259. the characteristic structural length scale – manifesting Poh, L.H. (2013): Scale transition of a higher order themselves in the homogenized solutions. This allows plasticity model – A consistent homogenization the- for a direct study on the interaction and competition ory from meso to macro – Journal of the Mechanics between the different micro-processes, with a low- and Physics of Solids, 61: 2692-2710. er computational cost compared to a detailed crystal plasticity model. 57 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Spectral Method Simulations of High Phase-Contrast Materi- als: A Joint Numerical–Experimental Study M. Diehl1, P. Shanthraj1, P. Eisenlohr2, C.C. Tasan1, F. Roters1, D. Raabe1 1Max Planck-Institut für Eisenforschung, Düsseldorf, Germany 2CHEMS, Michigan State University, East Lansing, MI, USA The spectral method has emerged as a powerful nu- high-resolution, 2D strain mapping methodology is merical tool to predict the mechanical response of employed, in which 3D effects are considered by a polycrystalline materials (Lebensohn et al. 2011) and post-mortem serial sectioning procedure. A promising its efficiency over finite flement methods has been correlation between the experiments and simulations demonstrated (Eisenlohr et al. 2013). Applications to is achieved, despite the complex micro-mechanics of heterogeneous materials with a large stiffness are, this material. Obtained strain maps reveal significant however, limited by the slow convergence of the it- strain heterogeneity arising from martensite disper- erative scheme. Various ideas have been proposed to sion, ferrite grain size, and defect densities effects; and overcome this issue, and we recently formulated di- early damage nucleation at notch-like irregularities in rect and mixed variational conditions for mechanical martensitic zones that cause high stress triaxiality. De- equilibrium and strain compatibility in a framework viations between experiments and simulations can be that couples them to a general class of non-linear solu- explained in terms of limitations of the involved tech- tion methods (Shanthraj et al. 2014). These formula- niques. tions are implemented in DAMASK, the Düsseldorf The presented integrated engineering approach pro- Advanced Material Simulation Kit (Roters et al. 2012). vides a high dimensional set of micro-mechanical out- A comparison on benchmark examples show, that the put information that can enhance the understanding solution method has a dominant influence on perfor- and further development of complex bulk multiphase mance and stability at large material heterogeneities, alloys (Tasan et al. 2014, Tasan et al. 2014). and improvements are obtained when higher-order solution methods are employed over the conventional References approach. Lebensohn, R. A., Rollett, A. D., & Suquet, P. (2011). Optimal solution strategies are devised based on this Fast fourier transform-based modeling for the de- and applied to a dual phase (DP) steel microstructure, termination of micromechanical fields in polycrys- created from an electron backscatter diffraction (EBSD) tals. JOM, 63(3), 13–18. based phase and orientation map. DP steels are used Eisenlohr, P., Diehl, M., Lebensohn, R. A., & Roters, F. as an application example to show, how the mechan- (2013). A spectral method solution to crystal elas- ical response of multi-phase alloys is governed by the to-viscoplasticity at finite strains. Int. J. Plast., 46, microscopic strain and stress partitioning behavior 37–53. among the various phases, crystals and subgrains. Due Shanthraj, P., Eisenlohr, P., Diehl, M., & Roters, F. to the limitations that are inherent in the experimental (2014). Numerically robust spectral methods for characterization of the stress-strain partitioning that crystal plasticity simulations of heterogeneous ma- takes place at the microscale, microstructure optimi- terials. Int. J. Plast., in press. zation of such alloys is typically based on the averaged Roters, F., Eisenlohr, P., Kords, C., Tjahjanto, D. D., Die- macroscale response (e.g. engineering stress-strain hl, M., & Raabe, D. (2012). DAMASK: the Düsseldorf curve). To strengthen the connection between micro- Advanced MAterial Simulation Kit for studying crys- structure and mechanical properties, a novel method- tal plasticity using an FE based or a spectral numer- ology is presented, that enables the joint experimental ical solver. In O. Cazacu (Ed.), Procedia IUTAM (Vol. and simulation-based analysis of the deformation-in- 3, pp. 3–10). duced evolution of heterogeneous materials with mul- Tasan, C. C., Diehl, M., Yan, D., Zambaldi, C., Shan thraj, tiphase microstructures. P., Roters, F., et al. (2014). Integrated experimen- This is achieved through a combined experimental-nu- tal-numerical analysis of stress and strain partition- merical approach, i.e. relying on in-situ deformation ing in multi-phase alloys. Acta Mat., 81, 386–400. experiments and crystal plasticity simulations both in- Tasan, C. C., Hoefnagels, J. P. M., Diehl, M., Yan, D., itiated from the same microstructural area of interest. Roters, F., & Raabe, D. (2014). Strain localization and For the experiments, deformation induced microstruc- damage in dual phase steels investigated by coupled ture evolution is tracked to increasing strain levels. To in-situ deformation experiments-crystal plasticity map local strains free of surface roughening effects, simulations. Int. J. Plast., 63, 198–210. a recently developed, digital image correlatiobased, 58 Talks Topic A 6: Multiscale phenomena in plasticity Influence of the microstructure of Al-components on the life time of integrated circuits F. Meier1, C. Schwarz, E. Werner 1Institute of Materials Science and Mechanics of Materials, Technische Universität München, Germany Growing demands on performance and durability of tion layer and the silicon substrate are supposed to be- integrated circuits (ICs) require an understanding of have elastically and temperature dependent. possible failure mechanisms. One main cause for dam- We investigate the influence of the microstructure on age of ICs arises from thermo-mechanical loads of the the stress and strain distribution within the model by involved materials as a result of current pulses. The changing the grains’ orientation, distribution and es- mismatch in thermal expansion leads to stresses which pecially size. Where possible, the simulation results are cause crack initiation and, in consequence, short cir- compared with experimental results taken from litera- cuits and the loss of functionality of the assembly. ture. Observations like surface roughening, crack initia- This study presents a series of numerical simulations tion and life extension when decreasing the aluminium using a three dimensional model considering alumin- film thickness can be predicted qualitatively correct. ium conductor paths sputtered on a silicon substrate and surrounded by a passivation layer. The ther- Acknowledgements mo-mechanical problem is solved utilizing the Abaqus/ This work has been conducted in the context of the Standard solver in combination with an user-defined research project SCHW 1347/3-1, funded by the DFG material subroutine which takes into account the mi- (Deutsche Forschungsgemeinschaft). We thank the crostructure, the grain orientation and size and the Max Planck Institut für Eisenforschung in Düsseldorf temperature dependent anisotropic visco-plastic ma- for providing the simulation kit DAMASK and for the terial behaviour of aluminium. Voronoi tessellation is open and constructive collaboration. used to model a realistic microstructure. The passiva- Deformation behavior of gradient materials with nanostruc- tured near surface regions Florian Rieger1, Andrey Molotnikov2,3, Xiaolei L. Wu4, Yuntian T. Zhu5,6, Thomas Böhlke1, Yuri Estrin2,3 1Chair for Continuum Mechanics, Institute of Engineering Mechanics, Karlsruhe Institute of Technology (KIT), Germany 2Department of Materials Engineering, Monash University, Clayton, Australia 3National University of Science & Technology “MISIS” Leninskii pr.4, 119049, Russia, Moscow 4State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China 5Department of Materials Science & Engineering, North Carolina State University, Raleigh, USA 6School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, China Materials processed by surface mechanical attrition ior of IF steel with a gradient microstructure produced treatment (SMAT) are attracting considerable inter- by SMAT through use of computational modelling. est. They possess extremely fine grain structure in a The proposed model is based on a microstructure-re- near-surface layer, while retaining a coarse grained lated constitutive description in which the dislocation (CG) interior. The experimental observations by various density is considered as a scalar internal variable (Es- groups (Wu et. al 2014, Lu 2014) have demonstrated trin, 1996). The model accounts for the grain size de- that such materials exhibit a favorable combination of pendent dislocation density evolution and also incor- strength and ductility. Computational models are re- porates the Kachanov-type damage model to predict quired to accelerate the design of such materials with failure. The model parameters were obtained using microstructure architectured for better performance. uniaxial tensile test data for CG material and a nanos- This study aims at investigating the deformation behav- tructured strip as the two extremes. 59 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 The average grain size variation with the distance from References the surface was used as input for one-dimensional cal- Wu X, Jiang P, Chen L, Yuan F, Zhu YT (2014) Extraor- culations of different SMAT-processed IF steels. Under dinary strain hardening by gradient structure. the Taylor (iso-strain) assumption, calculations were Proceedings of the National Academy of Scienc- carried out and validated against experimental uniax- es.111:7197-201. ial tension data for different SMAT processing times. Lu K. (2014) Making strong nanomaterials ductile with A good predictive capability of the model was thus gradients. Science. 345:1455-6. demonstrated. Estrin Y. (1996) Dislocation-Density-Related Constitutive Modeling. In: Krausz AS, Krausz K, editors. Unified Constitutive Laws of Plastic Deformation. San Diego: Academic Press; p. 69. 60 Talks Topic A 7: Multiscale phenomena in plasticity Talks Topic A7: Multiscale phenomena in plasticity 61 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Modelling the thermomechanical behaviour of the polycrys- talline microstructure of dual phase steels during sheet bulk metal forming Stefan Loehnert, Sebastian Zeller, Peter Wriggers Institute of Continuum Mechanics, Leibniz Universität Hannover, Germany During the forming process of metals, heat is released which leads to a significant temperature dependence due to the dissipative nature of plastic deformations. of the hardening. This heat leads to an increase of the temperature with- The three dimensional geometry of the polycrystal- in the material. Depending on the speed of the forming line microstructure is modelled by means of randomly process the rising temperature can be significant and generated Voronoi-cells of different sizes. To each cell may cause undesired effects such as residual stresses a random crystal orientation is assigned. The fully cou- or additional distortions. Depending on the speed of pled initial boundary value problem is solved for differ- the forming process the heat conduction may lead to ent boundary conditions applied on the outer bound- larger or smaller increase of the temperature. Thermal ary of a representative volume element of the poly- strains may also lead to a loss of geometrical accuracy crystal. In contrast to the commonly used staggered of the formed part. It is thus essential to consider tem- schemes here the coupled problem is solved directly perature effects and the strong coupling between the leading to a more robust numerical behaviour and fast- mechanical and the thermal part of the metal forming er convergence. process. From the results of the microstructural simulations To motivate the development of an effective, homoge- eventually the effective material behaviour can be nized macroscopic material model that can be used in computed by means of a homogenization procedure. macroscopic metal forming simulations, the polycrys- talline microstructure of the material is considered. References This necessitates the thermo-mechanical extension Anand, L. & Gurtin, M.E. & Reddy, B.D. (2015): The of the available purely mechanical crystal plasticity stored energy of cold work, thermal annealing, and models. This extension of this crystal plasticity model other thermodynamic issues in single crystal plas- helps to explain macroscopically observable effects like ticity at small length scales. – International Journal a temperature dependent yield stress or a storage of of Plasticity, 64, 1-25 energy that cannot be retrieved by mechanical unload- Zaiser, M. (2013): The energetics and interaction of ing. In this contribution we focus on dual phase steels random dislocation walls. – Philosophical Magazine like the DP600. For the different constituents of the mi- Letters, 93, 387-394 crostructure different thermal effects can be observed Stainier, L. & Cuitino, A.M. & Ortiz, M. (2002): A micro- leading to the requirement of different thermo-me- mechanical model of hardening, rate sensitivity and chanical crystal plasticity models for each constituent. thermal softening in BCC single crystals. – Journal of The evolution of the dislocation density in the ferritic the Mechanics and Physics of Solids, 50, 1511-1545 part of the microstructure is temperature dependent Computational assessment of the microstructure-dependent plasticity of lamellar gray cast iron Mario Metzger1,2, Thomas Seifert1 1Offenburg University of Applied Sciences, Germany 2Fraunhofer Institute for Mechanics of Materials IWM, Freiburg, Germany This work focuses on the microstructure-dependent cal analyses by means of finite-element method. In the inelastic behavior of lamellar gray cast iron. It com- finite-element analysis, the metallic matrix is modeled prises the reconstruction of three dimensional volume with an elastic-plastic deformation law. The graphite elements by use of the serial sectioning method for inclusions are modeled nonlinear elastic in order to de- the materials GJL-150, GJL-250 and GJL-350. The ob- scribe the typical tension-compression asymmetry for tained volume elements are prepared for the numeri- this material class. The stress-strain curves obtained 62 Talks Topic A 7: Multiscale phenomena in plasticity with the microstructure-based finite-element models microstructure-based finite-element models correctly. agree well with experimental curves of tension and The initial inelastic flow direction is also computed at compression tests. Besides the analysis of the whole the onset of macroscopic yielding. The analysis show volume element, the scatter of the stress-strain re- that the inelastic flow is not normal the yield surface. sponse in smaller statistical volume elements is inves- Therefore, a new yield function is proposed that is able tigated. Numerical studies are performed to reduce to recompute the microstructure-dependent yield sur- computational costs. faces properly. Furthermore, the initial multiaxial yield behavior is Besides the monotonic loading of the volume ele- analyzed. Therefore, the reconstructed volume ele- ments, also cyclic loading conditions are applied. ments are loaded bi- and triaxially beyond macroscop- Therefore, the isotropic elastic-plastic deformation law ic yield. The shape of the obtained yield surfaces are of the matrix material is substituted with a kinematic compared to the surfaces of four continuum models hardening law. which, amongst others, are proposed in literature to The obtained stress-strain hysteresis of the microstruc- describe the inelastic behavior of gray cast iron with ture-dependent volume elements describe the experi- lamellar shaped graphite inclusions. It is found that mental data very well. none of these models is able to describe all features Subsequently the macroscopic yield surfaces of the of the macroscopic yield surfaces obtained with the volume elements are analyzed after cyclic preloading. A Multiscale approach for thermo-mechanical simulations of loading courses in cast iron brake discs Christoph Herrmann1, Stefan Schmid1, Daniel Schneider2, Michael Selzer1,2, Britta Nestler1,2 1Hochschule Karlsruhe, Institute of Materials and Processes, Germany 2Karlsruhe Institute of Technology, IAM - CMS, Germany This talk presents a multiscale approach for the simu- factors composed from micrographic analysis are used lation of coupled heat and stress evolution induced by to generate three-dimensional representative volume different loading courses in grey cast iron brake discs. elements (RVE) and to define the metallographic con- The concept integrates the microstructural properties stituents. The information serves as input parameters as homogenized material laws into the macroscopic to algorithmically construct cast iron microstructure. computations. Extensive experimental testing is re- The elastic and elasto-plastic material models of the quired to establish a complete set of material param- constituents are briefly elucidated. In order to sim- eters required to conduct thermo-mechanical simula- ulate the different material behaviour in tension and tions on a macroscopic length scale. In addition, the compression, a crack opening and crack closure mech- microstructure can vary within the disc due to differ- anism is included. The potential of complementing ences in wall thicknesses and cooling rates. and substituting experimental testing is shown by a In order to reduce the experimental effort and to esti- quantitative comparison of the simulation results with mate the influence of microstructure characteristics on experimental data at ambient temperature. Both, vir- macroscopic heat and stress distributions, simulations tual tension and compression tests are executed as on the mesoscopic scale resolving the heterogeneous well as a tension-compression cycle. The presented microstructure with graphite flakes in a cast iron matrix approach provides a first step into a versatile range of are conducted. The workflow to derive the elasto-plas- applications and illustrates a broad potential for future tic properties according to its microstructure is demon- challenges of multiscale modelling in the field of ther- strated for a typical cast iron material. Geometrical pa- mo-mechanical failure analysis. rameters of the graphite phase distributions and shape 63 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Multi-physics, Multiscale Modeling of Plastic Deformation in Plasma-Facing Components N.M. Ghoniem,1 J. Blanchard,2 D. Rivera 1), E. Gao 1, M. Wasfy 3, C. Martin 2 1 Mechanical & Aerospace Engineering Department, UCLA, Los Angeles, USA 2 Department of Eng Physics and Nuclear Engineering, University of Wisconsin, Madison, USA Plasma-facing components (PFCs) are exposed to un- structure is then represented as a polycrystal, and the precedented operational environments, thus requiring viscoplasticity model is used to describe plastic flow extraordinary research and development efforts. Phys- and reveal damage accumulation at grain boundaries. ics-based models of material behavior are urgently Experimental results will also be presented for the de- needed to design new alloys or material architectures pendence of the thermomechanical damage in tung- that can withstand the challenging and punishing con- sten test articles on the intensity and duration of the ditions of high heat flux, neutron irradiation, plasma plasma heat flux, from plasma exposure experiments ion bombardment and thermomechanical transients. in an arcjet facility at UCLA. These results are presented Advances in fundamental research on structural ma- in the context of an advanced Tokamak design with ag- terial degradation in a fusion environment serve two gressive physics assumptions. The paper will conclude distinct purposes: (1) enable a rational process of al- with an assessment of the viability of these structures loy design and optimization for service life and per- in a typical Fusion Nuclear Science Facility (FNSF). formance, and (2) have a connection with mechanical _________________________________________ design of fusion components. We present here a “Mul- a) This material is based upon work supported by the tiscale Modeling” strategy for determination of plastic U.S. Department of Energy, Office of Science, Office deformation and damage in large-scale plasma-facing of Fusion Energy Sciences, under Award Number DE- components. We focus on two main components: (1) FG02-03ER54708 with UCLA, and DE-FG02-98ER-54462 the blanket and first wall structure of a fusion energy with the University of Wisconsin, Madison. system (the ACT-2 Tokamak design), and (2) a test ar- ticle representative of an element of a plasma diver- References tor facing high heat flux. The method relies on the Shahram Sharafat, Aaron Aoyama, Nasr Ghoniem, Bri- creation of successive coarse-grained elasto-plasticity an Williams, “Design and Fabrication of a Flat-Plate models, with increased levels of spatial resolution and Multichannel He-Cooled Refractory HX for Divertor accuracy. At the largest scale, an elastic model with Applications,” Fusion Science And Technology, 60 several millions degrees of freedom is used to deter- (1), 203-207 (20110. mine the global stress and deformation, where the S Sharafat, AT Aoyama, N Ghoniem, „Assessment of structural model is coupled with heat transfer and flu- the DCLL TBM Thermostructural Response Based on id flow models. Critical Regions (CRs), where failure is ITER Design Criteria,“ Fusion Science & Technology likely to occur are identified. Each CR is then modeled 60 (1), 264-271 (2011) with a dislocation-density based, viscoplastic model T Crosby, NM Ghoniem, „Thermo-mechanical damage that describes the evolution of plastic strain and asso- of tungsten surfaces exposed to rapid transient plas- ciated dislocation densities, where the polycrystalline ma heat loads, „Interaction and Multiscale Mecha- nature of the structure is smeared out. A region of the nics 4 (3), 207-217 (2011). 64 Talks Topic A 8: Multiscale phenomena in plasticity Talks Topic A8: Multiscale phenomena in plasticity 65 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 A Continuum Model for Dislocation Dynamics in Three Di- mensions using the Dislocation Density Potential Functions Yang Xiang, Yichao Zhu Department of Mathematics, the Hong Kong University of Science and Technology, Hong Kong With the development of the micro-technology, an ef- ting stress field drives the motion of the dislocation fective model, which properly describes the mechani- ensembles. The derived continuum model using the cal properties of crystals of size from the order of mi- DDPFs are validated through comparisons with the crons to sub-millimeters is highly expected. This is be- DDD simulation and experimental observation. As cause for crystals at such physical length scales, there an application of the derived continuum model, the is still limitation in applying the existing plasticity the- ``smaller-being-stronger’’ size effect on crystal stren- ories, such as the discrete dislocation dynamical (DDD) gth observed in the uniaxial compression tests of mi- models or the phenomenological continuum plasticity cropillars is studied and an explicit formula between theories. Here a three-dimensional continuum model the yield stress σflow and the pillar size D is derived. homogenized from the underlying dynamics of the dis- The obtained formula shows excellent agreement with location substructures is derived by representing the the experimental observations and it is found that σflow existing dislocation ensembles with two dislocation scales with log(D)/D, which is not far from the empiri- density potential functions (DDPFs), denoted by ψ and cal power law σ ~D-mflow with 0 160 MPa until specimen failure. At the stress amplitude sa = 160 MPa cyclic softening is followed by cyclic hardening due to martensite for- mation, which results in a significant increase in life time, up to the ultimate number of cycles of Nu = 10 7 in HCF-regime (Fig. 1, white squares). In the VHCFrange also deformation induced martensite formation is ob- served. This transformation results in an endurance limit before the ultimate number of cycles N 8u = 5·10 is reached (Fig. 1, black circles). The cyclic hardening is driven by a deformation induced phase transformation from face-centered cubic austenite to body-centered cubic a´martensite and/or hexagonal emartensite. Fig. 1: HCF- and VHCF-Woehler curve at 300 °C The fatigue-related material behavior in the HCF- and VHCF-regime is characterized by microstructural inves- References tigations with scanning and transmission electron mi- Altpeter, I., et al. (2012): Early detection of damage croscopy as well as x-ray diffraction. The focus of these in thermo-cyclically loaded austenitic materials – in studies is the deformation induced martensite forma- Electromagnetic Nondestructive Evaluation (XV), tion, which significantly affects the cyclic deformation Vol. 36, Rao, B.P.C., Jayakumar, T. and Balasubrama- behavior and increases life time. nian, K., Eds., IOS, Amsterdam, pp. 130139. Sorich, A., Smaga, M. and Eifler, D. (2014): Influence of Acknowledgements cyclic deformation induced phase transformation on The authors thank the Ministry of Economy and Ener- the fatigue behavior of the austenitic steel X6CrN- gy (BMWi), Germany as well as the German Research iNb1810, Advanced Materials Research, Vols. 891- Foundation (DFG) for the financial support within the 892, pp 12311236. SFB 926 ‘‘Microscale Morphology of Component Sur- faces’’. Influence of the surface morphology on the cyclic deforma- tion behaviour of cryogenic turned metastable austenitic steel X6CrNiNb1810 Robert Skorupski, Marek Smaga, Dietmar Eifler, Tilmann Beck Institut of Materials Science and Engineering, University of Kaiserslautern, Germany In this investigation deformation induced α´-martensite the α’-martensite fraction from the maximum value of formation in the near surface microstructure was real- 25 vol.-% at a distance of 12 µm from the surface down ized using a low temperature turning process with car- to 0 vol.-% at 285 µm was measured. At higher feed, bon dioxide cooling in the cutting zone. Via variation of first an increase of the α’-martensite fraction from 9 the cutting parameters different near surface morphol- vol.-% at the surface to 37 vol.-% at 72 µm below the ogies can be formed. With optical micrographs of the surface and a following continuous decrease to zero near surface microstructure and additional micro hard- was measured. For both feeds, at the surface only the ness measurements it was proved that a surface layer two phases g-austenite and α’-martensite exist. The with a thickness of about 300 µm during the cryogenic ε-martensite was detected only below the surface (Au- turning process develops. Quantitative x-ray analysis rich, J., et al. 2014). The feed also influences the sur- of the cryogenic turned surface layers showed that the face topography, which affects significantly the fatigue feed f has a great influence on the resulting phase dis- strength in the high cycle fatigue regime. With increas- tribution. In addition to the paramagnetic fcc g-austen- ing feed rate the surface roughness increases and the ite and ferromagnetic bcc α’-marteniste a third phase, surface defects trough chip replacement decreases. the paramagnetic hexagonal ε-martensite, exists. Fur- The fatigue tests were performed on a servo-hydraulic thermore, for the small feed a continuous decrease of testing system using a triangular load-time function at 123 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 ambient (AT) and elevated temperatures (T = 300°C) in HCF range by stress control and a load frequency f = 5 Hz with the load ratio of R = -1. The benefit of the mar- tensitic surface layer on fatigue life can be clearly seen by the comparison of the fatigue life of a specimen loaded at AT after electrolytic polishing. The specimens with the martensitic layer reach the ultimate number of 2·106 cycles without failure whereas the specimens with austenitic surface layer fail ten times earlier. The plastic strain amplitude is significantly reduced by the deformation induced ma tensite layer caused by the restriction of dislocation mobility. Despite their larger roughness specimens with turned surface morphol- ogies reach the same number of cycles to failure as specimens with a polished austenitic surface. In analo- gy to results at AT the highest plastic strain amplitudes and consequently the shortest fatigue life at T = 300 °C are observed in specimens with an austenitic surface Fig. 1: Cyclic deformation curves of specimens with different layer after polishing. In fatigue tests at elevated tem- near surface morphologies, loaded with σa = 270 MPa at am- peratures specimens with a martensitc surface layer bient temperature reach, independent of the surface roughness, higher fatigue limits than specimens with austenitic surfaces References (Skorupski, R., et al. 2014). Skorupski, R., et al. (2014): Influence of Surface Mor- phology on the Fatigue Behavior of Metastable Acknowledgements Austenitic Steel. – Adv. Mat. Res. Vols. 891-892, pp. The authors thank the German Research Foun- 464-469. dation (DFG) for the financial support within the Aurich, J., et al. (2014): Characterization of deforma- SFB 926 ‘‘Microscale Morphology of Component tion induced surface hardening. – CIRP Annals - Surfaces’’. The fatigue specimens were turned at Manufacturing Technology, Bd. 63: 65-68. the Institute for Manufacturing Technology and Production Systems (FBK), University of Kaiser- slautern, Germany. We thank Prof. J.C. Aurich, Dr. B. Kirsch and P. Mayer for their support. Hybrid surface treatment on austenitic stainless steel JIS SUS316 to improve fretting fatigue strength Toshihiro Omori1, Tatsuro Morita2, Kohei Okada2, Hideaki Maeda1 1Torishima Pump Manufacturing Co., Ltd., Osaka, Japan 2Kyoto Institute of Technology, Kyoto, Japan Fretting is special wear which is induced by repeat- ed by simultaneous improvement in the friction-wear ed relative surface motion. This phenomenon often properties and the fatigue strength of metals. The occurs on the contact surfaces of combined machine above improvement can be achieved by appropriate parts and causes marked wear damage. If fretting was surface treatments. Moreover, the surface treatments induced under applied cyclic stress, it facilitates crack have an engineering advantage that there is no neces- initiation and greatly decreases fatigue strength (Endo sity of correcting the shapes of machine parts. & Goto 1976). Accordingly, the above phenomenon, In recent years, one of the authors has investigated the called fretting fatigue, has to be adequately prevented effect of various surface treatments such as plasma to assure the safety of the rotating machine products hardening treatments, fine-particle bombarding (here- such as turbines and water pumps. after, FPB), diamond-like carbon coating and their hy- The fretting fatigue is complicated because it is relat- brid surface treatments (Morita 2012, 2013). The re- ed to many factors such as friction-wear, metal fatigue, sults showed that the hybrid surface treatments were complex stress condition at contact surfaces and their more effective to improve the friction-wear properties interaction (Waterhouse 1992, Hoeppner 1994). How- and the fatigue strength than individual treatments. ever, it is expected that the fretting fatigue is prevent- From the above background, this study was systemati- 124 Talks Topic C 2: Cyclic deformation behavior, crack initiation & crack growth of metals cally conducted to investigate the effect of hybrid sur- ting fatigue strength. In the combination cases 1 and face treatment on the fretting fatigue strength of typ- 2, the fretting fatigue strength reached the same lev- ical austenitic stainless steel JIS SUS316. In this study, el and the improvement ratio was about 50 %. It was the hybrid surface treatment was composed of plasma thought that the above improvement resulted from nitriding and FPB (hereafter, PN/FPB). the simultaneous improvement in the wear resistance The fretting fatigue test was performed under the con- and the fatigue strength. dition in which two contact pads were pressed onto both sides of one fatigue specimen. The combinations References of fatigue specimen and contact pads are: 1. PN/FPBed Endo, K. & Goto, H. (1976): Wear 38, 311-24. specimen and contact pads; 2. PN/FPBed specimen Waterhouse, R.-B. (1992): Inter. Mater. Rev. 37, 77-97. and untreated contact pads; 3. untreated specimen Hoeppner, D.-W. (1994): Fretting Fatigue -in: Water- and contact pads for comparison. house, R.-B. & Lindley, T.-C. (eds.): Mech. Eng. Publi- The PN/FPB treatment formed a hardened layer. It cations, 3-19; London. gave no influence on the mechanical properties. The Morita, T. et al. (2012): Mater. Sci. Eng. A 558, 349-55. results of the fretting fatigue test showed that the PN/ Morita, T. et al. (2013): Mater. Trans. 54, 732-37. FPB treatment was very effective to improve the fret- Low cycle fatigue behaviors of hot-bent 347 Stainless Steels in a simulated PWR water Junho Lee, Jong-Dae Hong, Changheui Jang KAIST, Daejeon, Republic of Korea An austenitic stainless steel, SS347 is used for the pres- secondary hardening was not observed for the spec- surizer surgeline pipes in a pressurized water reactor imen tested in a PWR environment. Also, the cyclic (PWR). However, if the environmental fatigue is con- hardening behaviors showed some orientation depen- sidered per NRC Regulatory Guide 1.207 and NUREG/ dence, which was usually not observed for the as-re- CR-6909 (Chopra, 2014), fatigue design criteria would ceived pipes. The different cyclic hardening behaviors be difficult to be satisfied. To reduce the stress indi- were discussed in view of the microstructure and asso- ces as well as number of weld joints, hot-bending of ciated hot-bending process. The correlation between SS347 surgeline pipes is considered. Previously, there the LCF life and cyclic hardening behaviors was dis- have been some efforts to quantify the effects of sev- cussed also. In summary, the LCF behaviors of SS347 in eral factors considered in environmental fatigue, such both air and PWR environments were not significantly as temperature, strain rate, and water environments affected by the hot-bending. (Solin, 2013a; Solin 2013b). In this study, the effects of hot-bending on the low cycle References fatigue (LCF) in air and simulated PWR environments Chopra, O.K. & Stevens, G.L. (2014): Effect of LWR are investigated by tests and analysis. In the completed Coolant Environments on the Fatigue Life of Reactor hot-bent pipes, the amount of deformation and ther- Materials – NUREG/CR-6909(Rev. 1), Argon National mal cycle were different depending on the location of Laboratory; USA. the pipes, which in turn showed different LCF behav- Solin, J. & Reese, S. & Karabaki, H.E. & Mayinger, W. iors. The LCF of hot-bent SS347 is similar to or greater (2013a): Environmental Fatigue Factors (NUREG/ than that of the as-received one in room temperature CR-6909) and Strain Controlled Data for Stabilized air and PWR environments, though the scatter is large Austenitic Stainless Steel – Proceedings of the for the intrados and extrados where extensive defor- ASME 2013 Pressure Vessels and Piping Conference, mation was accumulated during the process. The fa- PVP2013-97500; France. tigue tested specimens were sectioned and analyzed Solin, J. & Reese, S. & Mayinger, W. (2013b): Long Life to observe crack morphology, secondary cracks, and Fatigue Performance of Stainless Steel – Proceed- effects of microstructure. ings of the ASME 2013 Pressure Vessels and Piping In general, cyclic hardening response of SS347 was Conference, PVP2013-57942; France. greater at room temperature and lower in PWR envi- Cho, H. & Kim, B.K. & Kim, I.S. & Jang, C. (2008): Low ronment, which is consistent with that of 316LN (Cho, cycle fatigue behaviors of Type 316LN austenitic 2008). Unlike 316LN, a clear secondary hardening was stainless steel in 310oC deaerated water – fatigue observed at room temperature for the as-received and life and dislocation structure development – Materi- hot-bent SS347 irrespective of the position. However, als Science & Engineering-A, 476: 248-256. 125 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Effect of Cold-Drawing on High-Cycle Fatigue Properties of Austenitic TWIP and Fully Pearlitic Steels Seok Weon Song1, Jeong Hun Lee2, Hyong Jik Lee3, Chul Min Bae3, Chong Soo Lee1,2 1Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Republic of Korea 2Department of Materials Science and Engineering, Pohang University of Science and Technology, Republic of Korea 3POSCO Technical Research Lab., Pohang, Republic of Korea This study aims to investigate the effect of cold-draw- fine striations on its ductile fracture-surface, while that ing on fatigue properties of austenitic twinning-in- of TWIP steel showed irregularly formed striations and duced-plasticity (TWIP) and fully pearlitic (FP) wire brittle fracture-surface. The different behavior in fa- steels. High cycle fatigue tests were carried out on two tigue crack propagation behavior was considered due different alloys, both of which were drawn to have to the difference in the amounts of dislocations accu- similar tensile strength of ~1500 MPa. Fatigue crack mulated near the grain boundaries or twin boundaries. propagation behavior and fracture mode were clear- By applying an appropriate heat-treatment, fatigue ly different in two alloys. The FP steel exhibited higher strength of TWIP steel was greatly increased without value of fatigue strength revealing well-developed and sacrifice of tensile strength. 126 Talks Topic C 3: Cyclic deformation behavior, crack initiation & crack growth of metals Talks Topic C 3: Cyclic deformation behavior, crack initiation & crack growth of metals 127 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Influence of characteristics of inclusion on rolling contact fa- tigue of bearing steel Eiichi Tamura, Yusuke Sandaiji, Takehiro Tsuchida Kobe Steel Ltd., Japan For the compact design of the bearing, higher fatigue ment results and analytical estimated results, analysis strength steel is expected to apply. In the bearing, fa- was found to be able to estimate that effect. From tigue crack is initiated from non-metallic inclusion due these comparisons, this 2D FEM analysis was found to to the cyclic shear stress caused by rolling contact. So simulate the actual crack initiation and growth behav- this rolling contact fatigue strength is thought to be in- ior. fluenced on by the characteristics of inclusions. How- Using this developed analytical method, the mecha- ever the effect factor of each characteristic is not clear, nism of crack initiation from inclusion and the effect because, with conventional rolling contact test, crack of some inclusion’s characteristics were discussed. initiating inclusion cannot be found on the fracture sur- Although It is easy to find that strain becomes lower face. when the Young’s modulus of the inclusion becomes In this research, to clarify the effect factor on the rolling closer to that of the matrix around inclusion and the contact fatigue, the analytical method was developed, size of the inclusion becomes smaller, furthermore, which is based on simple 2D FEM but can evaluate the it was found that, when the strength of the interface crack initiated area and the growth direction with con- between inclusion and matrix is zero, then the strain cerning the influence of cyclic loading. around inclusion becomes much higher. That is, the In 2D FEM analysis, repeatedly static loading was sub- interfacial peeling of inclusion was indicated to give stituted for the 3 cycle continuous rolling contact load- stronger influence to the fatigue life of the bearing than ing. During 1st cycle, the effect of compressive loading the inclusion’s size and Young’s modulus. By controlling was strong and the behavior was relatively unstable. the strength of interface betwen inclusion and matrix, But, after 2nd cycle, the effect of compressive loading it is expected that rolling contact fatigue strength of becomes so weak and the effect of cyclic shear defor- bearing steel becomes higher. mation becomes stronger and the strain behavior be- comes stable. And by analyzing strain behavior after References 2nd cycle around internal inclusion simulated part, Yaguchi, H. (2001): Effect of Non-Metallic Inclusions maximum strain range (Δεmax) distribution was evalu- of Rolling Contact Fatigue Life of Bearing Steels - ated and the location of maximum Δεmax, that is to say, Epilogue: Further Research Subjects – In: Journal of the location where the crack is the easiest to initiate, Japanese Society of Tribologists, 46-9: 702-705. was determined. Furthermore the direction of the Yamakawa, K., Kizawa, K., Oguma, N. & Kida, K. (2004): crack initiation and propagation was also determined. The Influence of Subsurface Defect on Stress Distri- Comparing the measurement result of the crack butions under Rolling Contact Fatigue Conditions － growth around the inclusion to analysis result, the lo- In: Koyo Engineering Journal, 166 : 24-28. cation of the crack initiation and the direction of the Nagao, M., Hiraoka, K. & Unigame, Y. (2005): Influen- crack growth are similar in both results. ce of nonmetallic inclusion size on rolling contact Furthermore by the comparison of the effect of inclu- fatigue life in bearing steel － In: Sanyo Technical sion type on crack initiation life between UT measure- Report, 12: 38-45. 128 Talks Topic C 3: Cyclic deformation behavior, crack initiation & crack growth of metals Evaluation of the fatigue behavior of damage tolerant TRIP-modified SAE 52100 steels using the short-time-proce- dures PHYBALCHT- and PHYBALLIT Marcus Klein, Hendrik S. Kramer, Tilmann Beck, Dietmar Eifler TU Kaiserslautern, Institute of Materials Science and Engineering, Kaiserslautern, Germany Different modules of the physically based fatigue life fied and two standard SAE 52100 - batches were com- calculation (PHYBAL) method for metallic materials pared to the estimations from the PHYBALLIT method. were developed in the last decade at the Institute of An increase of the ferromagnetic phase in constant Materials Science and Engineering at the University of amplitude tests above the fatigue limit indicates the Kaiserslautern. TRIP-effect. No phase transformation was observed at Enormous benefits of the “PHYBAL”-method are high and below the fatigue limit. It can be concluded that reliability and cost effectiveness as a result of the re- the TRIP-effect will not be activated in a component duction of the number of experiments in comparison loaded below the fatigue limit. to the conventional determination of fatigue data. The Type and size of the nonmetallic inclusions leading to application of the “PHYBAL”-method requires a very crack initiation have minor influence on fatigue life of limited number of high-precision fatigue experiments. the TRIP-modified SAE 52100 compared to the stand- In addition to conventional mechanical stress-strain ard batches. The reduced scatter in fatigue life confirms hysteresis measurements supplementary temperature the enhanced damage tolerance of the TRIP - modified and electrical measurements are used to characterize matrix. the fatigue behavior. All measured quantities are di- rectly influenced by deformation-induced changes of the microstructure of the bulk material and provide a high potential to estimate the endurance limit, to cal- culate woehler curves including consideration of mean stress as well as scatter bands, even for loading and material conditions leading to very limited cyclic plas- tic deformation. Recently the new short-time procedure PHYBALCHT was developed. This module requires only a planar materi- al surface to perform cyclic force-controlled hardness indentation tests. To characterize fatigue properties of metallic materials the change of the width of the force-indentation-depth-hysteresis ha,p has to be plot- ted versus the number of indentation cycles N. The Fig. 1. a) Hardness, retained austenite RA, hardening-expo- slope of the ha,p-N-curves and thus cyclic hardening can nentCHT eII of TRIP-modified SAE 52100, SAE 52100 - Batch I be described by the exponent eII. Consequently, eII is and - Batch II defined as hardening-exponentCHT. b) Comparison of the woehler curves. The size of the sym- In this study PHYBALCHT is used to identify promising bols represents the dimension of the nonmetallic inclusions, heat-treatment-parameters and alloying compositions which caused failure. of SAE 52100-TRIP steels. Fatigue cracks in SAE 52100 components quite often initiate at microstructural References imperfections like nonmetallic inclusions. Due to the Kramer, H; Starke, P.; Klein, M.; Eifler, D.: Cyclic Hard- wide spectrum of their size, microstructure, elastic ness Test PHYBALCHT - short-time procedure to eval- and adhesion properties, a high scatter in fatigue life uate fatigue properties of metallic materials, Int. J. is observed. The strategy in this investigation was to in- Fatigue, 78-84 (2014) duce local hardening and compressive residual stresses Starke, P.; Eifler, D.: Fatigue Assessment and Fatigue around imperfections by activating the TRIP-effect to Life Calculation of Metals on the Basis of Mechan- achieve an improved damage tolerance. ical Hysteresis, Temperature, and Resistance Data, One TRIP-modified SAE 52100 steel was selected for de- MP Materials Testing, 261-268 (2009) tailed investigations: Woehler curves of this TRIP-modi- 129 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 The development of the indirect method for estimation of strain life fatigue parameters Robert Basan1, Domagoj Rubeša2, Marina Franulović 1 1Faculty of Engineering, University of Rijeka, Rijeka, Croatia 2FH Joanneum GmbH, Graz, Austria Experiment-based determination of strain life fatigue essary data were gathered for a set of differently heat parameters σf’, b, εf’ and c although most accurate, treated high-strength low-alloy 42CrMo4 steels tested quickly becomes prohibitive due to the complexity and at room temperature. high costs of cyclic experiments (ASTM Standard E606). Performance of proposed indirect estimation method Monotonic tensile tests are simple and inexpensive, was evaluated using criteria which have been exten- and their results are usually readily available, so that sively used in different comparisons and verifications one of the methods for estimation of fatigue parame- of estimation methods reported in literature. Fatigue ters from material’s monotonic properties (Muralidha- lives calculated using estimated values of fatigue pa- ran, Manson 1988, Bäumel, Seeger 1990, Ong 1993, rameters are found to be in very good agreement Roessle, Fatemi 2000) is often used, especially during with those calculated using experimentally obtained early phases of product development. fatigue parameters. Furthermore, determined values Most of the existing methods for the estimation of of comparison criteria are significantly higher for pro- strain life parameters were developed by correlating posed method than those calculated for other estima- experimentally determined strain life parameters inde- tion methods. Proposed method will be extended and pendently of each other and directly with one or more adapted for estimation of fatigue parameters of unal- monotonic tensile material properties. In some cases, loyed, low- and high-alloy steels as well as aluminium this resulted in relatively complicated expressions for and titanium alloys in an extended paper. the calculation of fatigue parameters, while in others, because of the poor correlation between certain fa- References tigue and monotonic parameters, constant values were ASTM Standard E606, 1992 (1998). West Conshohock- assigned to some of these fatigue parameters. en (PA): ASTM International. Based on the previously proposed approach (Basan Muralidharan, U., Manson, S.S. (1988): A modified 2009, Basan et al. 2010) new, indirect method for esti- universal slopes equation for estimation of fatigue mation of strain life fatigue parameters from materials characteristics of metals. J Engng Mater Techn monotonic properties is proposed. Unlike the existing 1988;110:55–58. methods, proposed method is based on the identifi- Bäumel, A., Seeger, T. (1990): Materials data for cyclic cation and establishment of functional relationships loading – Supplement 1. Amsterdam: Elsevier; 1990. between selected monotonic property and ∆ε/2–2Nf Ong, J.H.: (1993): An improved technique for the pre- relations which is achieved by correlating ultimate diction of axial fatigue life from tensile data. Int J strength Rm and individual points on strain life curves. Fatigue 1993;15:213–219. From these established relationships, new values of fa- Roessle, M.L., Fatemi, A. (2000): Strain-controlled fa- tigue parameters σf’, b, εf’ and c were then determined tigue properties of steels and some simple approxi- for each value of the ultimate strength Rm so that new mations. Int J Fatigue 2000;22:495–511. functions σf’=f1(Rm) b=f2(Rm), εf’=f3(Rm) and c=f4(Rm) Basan, R. (2009): Fatigue and damage of the gear could be derived. Main advantage of the new approach tooth flank. Dissertation (in Croatian). Rijeka: and proposed method is that fatigue parameters (σf’, Faculty of Engineering, University of Rijeka b) and (εf’, c) are not estimated individually, i.e. inde- Basan, R., Rubeša, D., Franulović, M., Križan, B. pendently from one another. (2010): A novel approach to the estimation of For the development and a validation of the proposed strain life fatigue parameters. Procedia Engineering approach to the estimation of fatigue parameters, nec- 2010;2:417-426. 130 Talks Topic C 3: Cyclic deformation behavior, crack initiation & crack growth of metals Fatigue Properties of DLC Coated Steel AISI1045 with Cr Diffusion Layer on the Substrate Surface by AIH-FPP Process Kenta Ueyama1, Koji Kobayashi2, Hiroyuki Akebono1, Jun Komotori2, Atsushi Sugeta1 1Department of Mechanical Science and Engineering, Hiroshima University, Hiroshima, Japan 2Department of Mechanical Engineering, Keio University, Kanagawa, Japan In recent years, diamond-like carbon (DLC) films have These specimens were modified AIH-FPP process in attracted much attention in many industrial fields be- the chamber replaced by Ar gas. Shot particle was Cr cause of their properties, high hardness, chemical in- shot (30-50 µm in diameter), processing temperature ertness, biocompatibility. Especially, DLC films are well was 1473 K, peening time was 30 sec. In addition, for known for their excellent tribological properties, so comparison specimens, we prepared substrates which DLC films are attractive coating processes to achieve had not been performed AIH-FPP process. After AIH- energy savings and CO2 emissions reduction. However, FPP process, all specimens were coated with DLC films achieving higher adhesion of DLC films is an important using unbalanced magnetron sputtering (UBMS) to a task because poor adhesion between the films and the thickness of 2 µm (Cr interlayer 1 µm + DLC layer 1 µm). substrate limits the practical applications of DLC films. Fatigue tests were carried out by using an electro-mag- In this study, we focused on Atmospheric-controlled In- netic type bending fatigue testing machine in ambient duction Heating Fine Particle Peening (AIH-FPP) treat- air without any controls of the temperature and the ment system as a pretreatment to improve the adhe- moisture at a frequency of 20 Hz under the stress ratio sion between the DLC films and the substrate. AIH-FPP R = -0.8. The fatigue crack was observed continuously system has possibility to achieve the high adhesion by using a plastic replicas technique. strength compared with practical coating process by From the fatigue tests, it indicated that fatigue strength applying the Cr particle which indicates high chemical makes no difference regardless of Cr diffusion layer. So affinity to carbon which constitutes the DLC films as it was found that Cr diffusion layer hardly affected fa- shot material because AIH-FPP system can generate a tigue strength. On the other hand, fatigue strength of shot particle diffusion layer on the substrate surface. DLC coated specimen with Cr diffusion layer was higher The aim of this study is to examine the effects of Cr than it of other specimen. So DLC films can improve diffusion layer generated by AIH-FPP process on the fa- the fatigue strength of steel. Finally, in order to ex- tigue properties and fracture mechanism of DLC coat- amine the reason for that, fatigue crack initiation be- ed steel. havior was observed by replicas technique. From this The material (substrate) used in this study was a medi- observation, fatigue crack initiation life of DLC coated um carbon steel (AISI1045) having a carbon content of specimen was longer than other specimen. Therefore, 0.45%. After being machined into an hourglass-shaped it was clear that DLC films increased the fatigue crack specimen for fatigue tests, the specimen surface initiation resistance caused by the high compressive re- was polished using SiC paper and alumina powder. sidual stress and high hardness. 131 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Low cycle fatigue properties of the Fe-28Mn-5Cr-6Si-0.5NbC alloy Nobuo Nagashima, Takahiro Sawauchi and Kazuyuki Ogawa National Institute for Materials Science (NIMS), Japan Since the shape memory effect (SME) was discovered strain amplitude. The rupture life of the FMS alloy is 4 in Fe-30Mn-1Si (hereafter all compositions are in mass times higher at εta=0.6%, and twice at εta=0.9% and at %) single crystals by Sato et al. [1], which was followd εta=1.4% than the SUS304 steel. In addition, the stress by the development of polycrystalline Fe-30Mn-6Si al- amplitude of the FMS alloy is 1.5 times higher at εta loys by Murakami et al., the Fe-Mn-Si alloys undergo- =0.9 %, and twice at εta =0.6% than the SUS304 steel. ing face-centered cubic (fcc) (γ austenite) / hexagonal Deformation-induced α‘martensite in low cycle fatigue close-packed (hcp) (ε martensite) martensitic trans- test specimen of SUS304 has been detected with ferrite formation have attracted much attention. Aiming to meter, but was not detected in the FMS alloy.The low further develop these shape memory alloys (SMAs), cycle fatigue test specimen of FMS alloy ε martensite considerable efforts were made to induce corrosion re- (hcp) has been detected with X-ray diffraction analysis. sistance by alloying with Cr and Ni [3], and to improve Therefor the prolonged fatigue life of the FMS alloy is the SME by microalloying. In this way, SMAs with good attributable to the reversible deformation associated workability and reasonable cost have been developed. with the transformation pseudo-elasticity that can re- Recently, some of the present authors reported that duce the accumulated strain. an Fe-28Mn-6Si-5Cr-0.5NbC SMA showed signifi- cant damping capacity when subjected to cyclic ten- References sion-compression loading with strain amplitudes larger [1] A. Sato, E. Chishima, K. Soma, T. Mori, Acta Metall. than 10-3. Quantitative X-ray diffraction analysis and 30(1982) 1177. atomic force microscopy (AFM) performed in our pre- [2] M. Murakami, H. Otsuka, H.G. Suzuki, S. Matsuda, vious report [4] proved that reverse martensitic trans- in:Proc. Int. Conf. Martensitic Transformation, Japan formation of tensile-stress-induced martensite took Institute of Metals, 1986, pp. 985–990. place when the specimen was compressed back to zero [3] L.J. Rong, Y.Y. Li, C.X. Shi, Scripta Metall. Mater. strain. In this study, we conducted a low-cycle fatigue 34(6) (1996) 993. testing in the Fe-28Mn-6Si-5Cr-0.5NbC (FMS) alloy and [4] T. Sawaguchi, P. Sahu, T. Kikuchi, K. Ogawa,S. Ka- the SUS304 steel. jiwara, A. Kushibe, M. Higashino, T. Ogawa, Scripta The FMS alloy was prepared by vacuum induction Materialia, 54(2006), 1885 melting followed by hot-forging and rolling. A solution [5] Baruj A, Kikuchi T, Kajiwara S, Shinya N. Mater Sci treatment was carried out at 1470 K for 10 h. Then Eng A 378(2004):333. a thermomechanical treatment, consisting of 14% warm-rolling at 870 K and subsequent aging at 1070 K Tab. 1: Low-cycle fatigue test results for 10 min was performed to produce fine precipitates Nf σa ε ε ε of NbC carbides. The choice of the above mentioned ta pa ea alloy composition and the thermomechanical treat- SUS 164 607 0.020 0.0157 0.0043 ment refers to our earlier study [5]. 304 304 524 0.014 0.0106 0.0034 The fatigue tests were made using a servo hydraulic fa- Steel 1600 413 0.009 0.0065 0.0025 tigue testing machine of capacity 50kN, at maximum 5250 317 0.006 0.0042 0.0018 total strain amplitudes (εta) of 2.0%, 1.4%, 0.9%, 0.6%. 157 722 0.020 0.0140 0.006 Deformation microstructure after fatigue testing, were FMS 631 711 0.014 0.0082 0.0058 analyzed using ferrite meter and X-ray diffraction anal- ysis. alloy 3315 679 0.009 0.0041 0.0049 In the SUS304 steel, with decrease in applied strain 18290 618 0.006 0.0016 0.0046 amplitude, stress-strain hysteresis loop is reduced. On the other hand, the stress response of the FMS alloy is almost unchanged, irrespective of the applied 132 Talks Topic C 4: Cyclic deformation behavior, crack initiation & crack growth of metals Talks Topic C 4: Cyclic deformation behavior, crack initiation & crack growth of metals 133 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Effects of nitriding temperature on the fatigue properties of Ti-6Al-4V alloy and in-situ observation of fatigue cracks in 4-points bending Shoichi Kikuchi1, Sho Yoshida2, Yuta Nakamura2, Akira Ueno2, Yoshikazu Nakai1 1Department of Mechanical Engineering, Kobe University, Japan 2Department of Mechanical Engineering, Ritsumeikan University, Kusatsu, Shiga, Japan Nitriding has been widely applied in various fields of compound layer was formed on Ti-6Al-4V alloy nitrided engineering to improve wear resistance of material at the temperature higher than 600 oC. because nitriding can form high hardness layers; a ni- The fatigue strength of the nitrided specimens was in- trogen compound layer and a nitrogen diffusion layer creased with decreasing nitriding temperature. Espe- (Morita et. al 1997 and Shibata et. al 1994). The aim cially, the specimens nitrided at 550 oC without nitride of this study is to examine the effects of nitriding on compounds showed higher compared to the un-nitrid- the fatigue properties and fatigue crack propagation ed specimen. On the other hand, fatigue strength of behavior of Ti-6Al-4V alloy in 4-points bending. the specimens nitrided at 850 oC was much lower than The material used in this study was the α + b titani- that of the un-nitrided specimen. These results im- um alloy (Ti-6Al-4V). Titanium plates were machined ply that nitrogen compound layer reduces the fatigue into the specimens with 4 mm in width and 40 mm in strength of Ti-6Al-4V alloy. length using a wire-electrical discharge machine. These Fatigue fracture mechanism of the nitrided specimen specimens were polished with emery papers (#320 to was discussed from viewpoints of fractography. In this #4000) to 3 mm in thickness and mirror-finished using study, every specimen exhibited the surface fracture SiO2 suspension. Nitriding was performed at 550 oC, modes. Characteristic flat area; corresponding to the 600 oC and 850 oC for 5 h on the basis of the previous thickness of compound layer, was clearly observed at study (Kikuchi et. al 2014). Surface hardness of the ni- the nitrided specimen. As results of in-situ observa- trided specimens was measured using a micro-Vickers tions of fatigue cracks, life of fatigue crack initiation hardness tester. The surface microstructures of the was short due to the existance of surface compound specimens were characterized using an optical micro- layer. Nitrogen compound layer shows brittle fracture scope, scanning electron microscopy (SEM), X-ray pho- during fatigue tests and adversely affects the fatigue toelectron spectroscopy (XPS), X-ray diffraction (XRD) properties of titanium alloy. with CuKα radiation and electron backscatter diffrac- tion technique (EBSD). References 4-points bending fatigue tests were performed in am- Morita, T., Takahashi, H., Shimizu, M., & Kawasaki, K. bient air without any controls of the temperature and (1997): Factors controlling the fatigue strength of the moisture at a frequency of 20 Hz under the stress nitride titanium – Fatigue & Fracture of Engineering ratio R = 0.1 and 0.5. For some specimens, in-situ ob- Materials & Structures. 20: 85-92. servation of fatigue cracks was conducted using a mi- Shibata, H., Tokaji, K., Ogawa, T., & Hori, C. (1994): The croscope and digital video camera. After testing, the effect of gas nitriding on fatigue behavior in tita- fracture surfaces were observed using SEM. Moreover, nium alloys – International Journal of Fatigue. 16: K-decreasing tests were conducted for the un-nitrided 370-376. DC(T) specimen. Kikuchi, S., Nakamura, Y., Ueno, A., & Ameyama, K. Surface hardness of titanium alloy was increased with (2014): Development of low temperature nitriding nitriding temperature. Specimens nitrided at 600 oC process and its effects on the 4-points bending and 850 oC exhibited the X-ray diffraction peaks of sub- fatigue properties of commercially pure titanium – strate and nitrogen compounds. In contrast, the XRD Advanced Materials Research. 891-892: 656-661. and XPS analyses indicate that a nitrogen diffusion layer without nitrogen compounds is formed on the specimen nitrided at 550 oC. It was found that nitrogen 134 Talks Topic C 4: Cyclic deformation behavior, crack initiation & crack growth of metals The influences of foreign object damage on the high cycle fa- tigue behavior of titanium alloy TC11 Zhao Zhenhua1, Chen Wei1,2, Wu Tieying1 1College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Jiangsu Province Key Laboratory of Aerospace Power System, Nanjing, China 2Collaborative Innovation Center of Advanced Aero-Engine, Nanjing, China When the plane takeoff and landing, the foreign With the same size of foreign objects, the damage area objects, including stones and gravels of different sizes enlarges with the increasing of impact velocity, and and shapes, can be ingested into the aero-engine and more micro cracks and lamellar structures emerge. The cause damages on the fan or compressor component high cyce fatigue strength of damaged TC11 speciments (Nicholas 2006). The damage, commonly referred to as after impact was determined by fatigue tests employ- Foreign Object Damage(FOD), is typically in the form of ing step loading test method. The results indicate that notching, including a wide range of notch depth, radius, there is obviously descend in the fatigue strength of and possible cracking at the root of the notching. FOD damaged speciments. And the fatigue strength de- can reduce the fatigue life of those components sub- creases with the depth of damage increasing. jected to vibratory loading. Peters (2000) investigated The SEM observations on the fatigue fracture surface the influence of FOD on the high cycle fatigue indicate that the fatigue source locates in the surface performance of Ti-6Al-4V and analyzed the effect of of damage area, and initiates from the micro cracks micro-cracking caused by impact on the process of or micro notches caused by impact. Under similar fatigue crack initiation. Mall(2010) discovered the conditions of macroscopic damage, the fatigue distinctly different damage mechanisms caused by strength of specimen impacted with higher impact different damage simulated methods. velocity is inferior to that impacted with lower impact In this paper, the effect of FDO on fatigue performance velocity. of aircraft engine fan/compressor blade material TC11 titanium alloy were investigated. Foreign object dam- References age (FOD) test on TC11 titanium alloy plate speciments Nicholas, T. (2006): High Cycle Fatigue: A Mechanics were conducted using gas gun test system. The steel Of Materials Perspective[M]. Elsevoer Ltd. spheres of 2 mm and 3 mm diameter were employed Peters, J.O., Roder, O., Boyce, B.L., Thomson, A.W. & and the launching vleocity was in the range of 250~400 Ritchie, R.O. (2000): Role of Foreign Object Damage m/s. The macroscopical and microscopical character- on Thresholds for High-Cycle Fatigue in Ti-6Al-4V. istics of specimen damage were observed by three-di- Metallurgical and Materials Transactions., 31A: mensional digital microscope and scanning electron 1571-83 microscope (SEM) respectivey. It is found that the mac- Mall, S. Hamrick, II. Joseph, L & Nicholas, T. (2001): roscopical damage mainly involves the material extru- High Cycle Fatigue Behavior of Ti-6Al-4V with Simu- sion deformation, shear loss and plastic deformation, lated Foreign Object Damage. Mechanics of Materi- while the microscopical damage mainly involve the mi- als., 33: 679–92. cro cracks, plastic deformation, micro notches and etc. Effect of forging condition on fatigue behavior in AZ61 bulk nanostructured metal fabricated by multi-directional forging Yoshihiko Uematsu1, Toshifumi Kakiuchi1, Taishi Nozaki1, Hiromi Miura2 1Gifu University, Gifu, Japan 2Toyohashi University of Technology, Toyohashi, Japan Magnesium (Mg) alloys are attractive as structural of materials. Recently, many sever plastic deformation materials due to their light weight and high specific (SPD) methods, such as multi-directional forging (MDF), strengths. But 0.2% proof stress and tensile strengths equal channel angular pressing (ECAP), high-pressure are still lower than conventional light weight alloys torsion (HPT), accumulative roll bonding (ARB) and so such as Ti and Al alloys. It is well known that grain re- on, are proposed to achieve very fine grains by SPD. finement is effective to improve mechanical properties In MDF technique, the material is forged with chang- 135 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 ing forging direction 90 degrees pass-by-pass. In the or slightly decreased compared with 3path specimen. present study, MDF was applied to AZ61 magnesium Consequently, fatigue limits, which are defined as alloy to achieve bulk nanostructured metal. Fully fatigue strengths at 107 cycles, are not in accordance reversed axial fatigue tests were conducted using with Hall-Petch relationship. MDFed AZ61. The number of forging path was changed As mentioned above, the fatigue strength was not as 1, 3, 6 and 8, and the effect of forging condition on further increased by the 6th and 8th paths forging fatigue behavior was investigated. process. Thus the surface morphologies after fatigue The microstructural observation revealed that the loading were examined in detail by a scanning average grain size becomes smaller with increasing electron microscope (SEM). After fatigue loading, the forging paths. The minimum grain size was about surface roughness was increased in 6path and 8path 0.3μm, while that of the as-received material was specimens. The peak-to-peak distances on the fatigue- 21.6μm. The average grain size was 21.6μm, 19μm, loaded samples were nearly the same with the average 0.6μm and 0.3μm for the as-received, 1path, 6path and grain sizes in both specimens. It indicates that grain 8path materials, respectively. The hardness and tensile boundary slipping might have occurred. In fine-grained strength increased with decreasing average grain size, Mg alloys, grain boundary slipping could easily occur. and the mechanical properties corresponded to Hall- Consequently, it is considered that 6path and 8path Petch relationship. materials had very fine grains resulting in grain bound- Subsequently, fully reversed axial fatigue tests had ary slipping during fatigue loading, and thus fatigue been performed. It was found that the fatigue strengths strengths were not further improved by 6th and 8th path increased with increasing forging path number up to 3 because the operation of grain boundary slipping had times. However, when the forging path number was 6 detrimental effect on fatigue strength. and 8, the fatigue strengths of are nearly the same with Variable-Amplitude of Aluminum Alloy 7075 in the VHCF Re- gime under Superimposed Loading Conditions S.E. Stanzl-Tschegg, M. Meischel, N. Iyyer, A. Arcari, N. Phan BOKU, Vienna, Austria Characterizing the material behaviour below the tradi- were studied by using a spectrum composed by a low tional endurance limit, the threshold between high-cy- frequency carrier wave at 0.01, 2 and 5 Hz and a su- cle-fatigue (HCF) and very-high-cycle-fatigue (VHCF), is perimposed high-frequency wave at 20 kHz. The low an important step towards understanding the signifi- frequency wave is assumed sinusoidal or rectangular cance of a fatigue limit usage in life calculation with the shaped, the high-frequency wave has constant and strain life methods. The aim of this study is to quantify variable amplitudes and the effects of different loading the influence of VHCF cycles on fatigue life of 7075-T6 sequences are investigated. For a better understanding Al-alloys using both constant and variable amplitude of the relevant mechanisms, the initiation and growth loading. Constant amplitude loading tests with and of small and long cracks were measured. Correlating without superimposed mean levels were performed the measurement results with microscopic surface ob- to characterize the material behaviour in fatigue with servations and SEM fracture surface studies allowed minimal effect of load interactions. These tests helped identification of surface and interior fatigue crack ini- advancing hypothesis, elucidating the role of mean tiation and propagation. Predictions based of the ob- stresses and understanding the scatter of fatigue data. tained data and appropriate modeling of the different The effects of combined cycle fatigue (CCF) loadings mechanical processes are detailed. 136 Talk Topic C 5: Cyclic deformation behavior, crack initiation & crack growth of metals Talk Topic C 5: Cyclic deformation behavior, crack initiation & crack growth of metals 137 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Assessment of fatigue crack closure under in-phase, out-of- phase and phase-shift thermomechanical fatigue loading us- ing a temperature dependent strip yield model Carl fischer1,2, Christoph schweizer1, Thomas seifert2 1Fraunhofer Institute for Mechanics of Materials IWM, Freiburg, Germany 2Offenburg University of Applied Sciences, Offenburg, Germany In high temperature components mechanical and ther- as fatigue crack retardation after overloads. mal loads are acting at the same time during start-up In this paper fatigue crack closure under in-phase, out- and shut-down cycles resulting in thermomechanical of-phase and phase-shift thermomechanical fatigue fatigue (TMF) of the materials. Gas turbines are clas- loading is studied using a temperature dependent strip sical examples of such components where nickel-base yield model. It is shown that fatigue crack closure is alloys are used in the hot parts. Above 750 °C the yield strongly influenced by the phase relation between me- stress of nickel-base superalloys becomes strongly chanical loading and temperature, if the temperature temperature dependent. difference goes along with a temperature dependence As a consequence of the temperature dependent yield of the yield stress. In order to demonstrate the effect of stress, the mean stress strongly changes with the ap- the temperature dependent yield stress, the influence plied phasing of thermal strains and mechanical strains. of in-phase, out-of-phase and phase-shift TMF loading Typically, tensile mean stresses arise during out-of- is studied for a polycrystalline nickel-base superalloy. phase (OP) TMF loading, while in-phase (IP) TMF load- By using a mechanism based lifetime model, implica- ing usually leads to compressive mean stresses. tions for fatigue lives are demonstrated. It is shown, For isothermal loading it is known, that the mean stress that fatigue crack closure can explain that in-phase affects fatigue crack growth and fatigue lives. Higher thermo mechanical fatigue tests show lower lifetimes mean stresses lead to faster fatigue crack growth and at high mechanical loadings than out-of-phase tests thus to shorter fatigue lives. However, under TMF load- and that the lifetime curves cross each other at lower ing, IP TMF tests with negative mean stresses often mechanical loadings. show shorter fatigue lives than OP TMF tests at high mechanical loadings. At low mechanical loadings this References trend can be reversed (see Guth et al. (2014)). Guth, S. et al. (2014): Lifetime, cyclic deformation and In mechanism based lifetime approaches the mean damage behaviour of MAR-M247 LC under thermo- stress effect is accounted for by fatigue crack closure mechanical fatigue loading with 0°, 180°, -90° and models. Since fatigue crack growth in ductile metallic +90° phase shift between strain and temperature. – materials involves irreversible plastic deformations at Procedia Engineering 74 (2014) 269-272. least in a small zone around the crack-tip, plasticity Newman, J. C. (1981): A crack-closure model for pre- induced fatigue crack closure, which is the dominant dicting fatigue crack growth under aircraft spectrum mechanism for the explanation of mean stress effects, loading – In: J. B. Chang, C. M. Hudson (eds.): Meth- immediately becomes history dependent, too. The ods and Models for Predicting Fatigue Crack Growth strip yield model from Newman (1981) has proven to under Random Loading. ASTM STP 748, American be a powerful tool to examine load history effects such Society for Testing of Materials, 1981, 53-84. 138 Talk Topic C 5: Cyclic deformation behavior, crack initiation & crack growth of metals Dwell time effects on the Thermo-Mechanical Fatigue Be- haviour of a Wrought Ni-base Alloy Stefan Guth, Jonas Müller, Karl-Heinz Lang Karlsruhe Institute of Technology, Germany The influence of dwell times on lifetime, cyclic defor- duced amount of secondary carbides precipitating in mation and damage behaviour of the wrought Ni-base dwell tests. Cracks propagate mainly intergranular in alloy NiCr22Co12Mo (comparable to Inconel Alloy 617) IP and CCD tests for both dwell times and continuous under thermo-mechanical fatigue (TMF) loading was tests. Damage occurs in form of wedge type cracks at studied. Strain controlled TMF tests with a tempera- grain boundary triple junctions. The cracks show a high ture range of 100 – 850 °C and dwell times of 0, 2, 5 angle to the stress axis and tend to interconnect when or 30 min at 850 °C were conducted in air. Mechani- growing. In dwell time tested specimens additional cal strain amplitudes varied from 0.3 to 0.7 %. Phase round type cavities could be found. Crack propagation angles between mechanical strain and temperature in OP and CD tests was predominantly transgranular were 0° (in-phase, IP), 180° (out-of-phase, OP), +90° and similar for continuous and dwell time tests. Some (clockwise diamond, CD) and -90° (counterclockwise specimens showed internal wedge type cracks under diamond, CCD). Light microscopy was used to observe a low angle to the stress axis that remain relatively damage on longitudinal sections of cycled specimens. small. The occurrence of wedge type cracks with di- Microstructural evolution was studied using transmis- rection dependent on the phase angle indicates that sion electron microscopy (TEM). grain boundary sliding accumulates during testing (Fu- The introduction of a dwell time in IP and CCD tests jino 1979). The somewhat unexpected effects of dwell resulted in a prolonged lifetime compared to tests times on lifetime are discussed on the basis of the ob- without dwells although the plastic strain amplitude served deformation and damage behaviour. increased. With increasing dwell duration the lifetime decreased. However, shortest life was found in contin- Reference uous tests. Lifetimes under OP and CD phasing were Fujino, M. and Taira, S. (1979): Effect of thermal cycle not significantly influenced by dwells. The saturated on low cycle fatigue life of steels and grain bound- stress amplitudes in dwell tests were in general about ary sliding characteristics. – In: ICM 3, Camgbridge, 30 % lower than in comparable continuous tests. TEM England, Volume 2, 49 - 58 investigations indicate that the reason for this is a re- 139 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Biaxial fatigue behavior of a hot-pressed metastable auste- nitic steel Stephanie Ackermann, Tim Lippmann1, Sebastian Henkel, Horst Biermann Technische Universität Bergakademie Freiberg, Institute of Materials Engineering, Freiberg, Germany Biaxial fatigue is an important load state occurring in crack type A according to (Brown & Miller 1973) and structural components. Higher fatigue lives under shear the absence of crack opening normal stress (Doquet loading were reported in literature for several materi- 1997) are possible reasons. als (Doquet 1997). Pure shear fatigue can be studied by Thus, surface cracks were investigated at different using biaxial-planar tests with cruciform specimens. In states of fatigue life and after fatigue failure in order the present study cyclic deformation tests were carried to clarify the higher fatigue lives under shear fatigue. out at room temperature under total strain control. A Different techniques were used such as electron beam variety of biaxial states of strain were set by varying universal system, replica technique, light optical mi- strain ratio between the axial strain amplitudes from croscopy, backscatter electron contrast and electron -1 to 1. Straining with a strain ratio of -1 correspond to backscatter diffraction in a high-resolution field emis- pure shear as well as pure torsion. sion scanning electron microscope. The investigated material is a high alloy metastable Different types of macro cracks on the sample surface austenitic stainless CrMnNi steel which was produced which caused fatigue failure were observed. Cracks af- by hot-pressing. The steel exhibits martensitic trans- ter shear fatigue were oriented 45° to the loading axes. formation from austenite via ε-martensite into α‘-mar- This direction corresponds to maximum shear strain tensite during cyclic deformation. The α‘-martensite direction which is mode II (Itoh et al. 1994). In addi- formation causes cyclic hardening and depends on the tion, crack branching was observed. Crack directions plastic strain amplitude as well as on the accumulated perpendicular to the loading axes which corresponds plastic strain. The dominating deformation structures to mode I were observed after biaxial cyclic deforma- are stacking faults and deformations bands wherein tion with strain ratios of 1, 0.5, -0.1 and -0.5 as well. α‘-martensite is formed. These results confirm the findings in literature (Itoh et Cyclic shear deformation (strain ratio = -1) caused the al. 1994, Parsons & Pascoe 1976). earliest beginning of martensite formation and the highest volume fractions of α‘-martensite at fatigue References failure in comparison to uniaxial and other biaxial Doquet, M. (1997): Crack initiation mechanisms in tor- states of strain. The maximum α‘-martensite contents sional fatigue. – Fatigue Fract. Eng. Mater. Struct., were 25-50 % higher under shear than under equibiax- 20: 227-35. ial loading (strain ratio = 1). Itoh, T. & Sakane, M. & Ohnami, M. (1994): High Tem- In accordance to the literature using von Mises equiv- perature Multiaxial Low Cycle Fatigue of Cruciform alent strain amplitude (Doquet 1997, Itoh et al. 1994), Specimen. – Trans. ASME, 116: 90-98. cyclic shearing caused higher fatigue lives after fatigue Brown, M.W. & Miller, K.J. (1973): A Theory for Fatigue failure than other biaxial and uniaxial conditions. The Failure under Multiaxial Stress-Strain Conditions. – Basquin and Manson-Coffin assessment is appropriate Proc. Inst. Mech. Eng., 187: 745-55. to correlate the fatigue life of uniaxial and biaxial load- Parsons, M.W. & Pascoe, K.J. (1976): Observations ing conditions, but is too conservative for shear fatigue. of Surface Deformation, Crack Initiation and Crack It is assumed that the period of crack initiation is much Growth in Low-cycle Fatigue under Biaxial Stress. – longer under shear fatigue in comparison to other Mater. Sci. Eng., 22: 31-50. studied biaxial conditions. Moreover, the uncritical 140 Talk Topic C 5: Cyclic deformation behavior, crack initiation & crack growth of metals High temperature low cycle fatigue behavior of cast super- alloy Inconel 713LC coated with ZrO2-SiO2-Al2O3 nanocrystal- line thermal barrier coating Karel Obrtlik1, Ladislav Čelko2, Tomáš Chráska3, Ivo Šulák1, Lenka Klakurková2, David Jech2, Vik- tor Škorík1, Jiří Švejcar2 1 Institute of Physics of Materials, AS CR, Brno, Czech Republic 2 Brno University of Technology, CEITEC, Brno, Czech Republic 3 Institute of Plasma Physics, ASCR, Praha, Czech Republic Cast polycrystalline nickel base superalloy Inconel using water stabilized plasma the top coat was formed 713LC is used for production of blades and discs of in partially crystalline phase. Its subsequent heat treat- gas turbine engines that are subjected to repeated ment enabled to produce the nanocrystalline mullite elastic-plastic loading in aggressive environments at phase in the remaining mostly ZrO2 and Al2O3 coating variable temperatures. Thermal barrier coatings (TBCs) matrix. consist of thermally insulating ceramic top coat and of Button-end samples with dimensions close to the final a metallic oxidation/corrosion-protective bond coat. specimens were manufactured using investment-cast- They can prolong the component life particularly by a ing. Cylindrical specimens of Inconel 713LC in as-re- reduction of temperature gradient during heating and ceived condition and with TBC surface treatment were cooling. cyclically strained under strain control with constant In the present work, the high temperature low cycle total strain amplitude in symmetrical cycle at 900 °C fatigue behavior of cast nickel-based superalloy Inco- in air. nel 713LC in as-received state and coated with novel The microstructure of the surface treated layer was Al2O3-SiO2-ZrO2/CoNiCrAlY TBC system was studied at documented and the hardness of the layers was eval- the temperature of 900 °C. The microstructure of the uated. Hardening/softening curves, cyclic stress-strain substrate material consisted of dendritic grains with curve and fatigue life data of coated and uncoated carbides and shrinkage pores. The average grain size material were obtained. The fracture surface, surface was 0.66 mm. relief and polished sections parallel to the specimen The novel TBC system consists of a (inter)metallic CoN- axis were examined using optical microscopy and SEM iCrAlY bond coat and a eutectic ceramic, i.e. zirconia to study damage mechanisms in cyclic loading at high (ZrO2), alumina (Al2O3) and silicia (SiO2) top coat depos- temperature. The microstructural and degradation ited on the gauge section of cylindrical specimens using mechanisms data help to discuss the differences in the atmospheric gas stabilized plasma and water stabilized stress-strain response and fatigue life of both materi- plasma, respectively. Due to the system of eutectic als. ceramic coupled with high temperature developed by 141 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Optimal Design of Skirt Supporting Structure of Coke Drum for Thermal-Mechanical Cyclic Loading Edward Wang, Zihui Xia Department of Mechanical Engineering, University of Alberta, Edmonton, Canada Coke drums are vertical clad pressure vessels used in with the actual drum. Due to large radial expansion of petroleum refineries to facilitate the delayed coking the shell that may cause contact of the shell and the process. The drums are operated under severe ther- skirt surfaces , contact elements are specified near the mal-mechanical conditions due to cyclic heating and junction corner. cooling of the drums. Most existing coke drums are In this study, slot dimensions are manipulated to opti- supported by a continuous cylindrical shell commonly mize the slot dimensions for minimal junction stress. referred to as the skirt. They are often joined tangen- The slots currently used are typically narrow in rela- tially to the vertical portion of the vessel by a contin- tion to their circumferential spacing, representing a uous fillet weld. Stresses in this junction are very high decrease of only about 3% in the moment of inertia due to the combination of physical constraints and compared to a solid skirt. Contrary to earlier findings, thermal-mechanical loading of the vessel. Under cyclic no significant difference is found in the average and loading, these stresses may induce fatigue failure. In a maximum junction stress between the solid (without previous study, it was found by means of an analytical slots) and current slotted skirt designs. In addition, it solution that slotting the skirt, and thereby reducing its is found that the junction stress shows no significant overall stiffness near the junction, can reduce junction response to the distance between the slot and junction stress (Cheng and Weil). However, the effect of slotting based on the current slot size. Furthermore, It is found the skirt can be studied in more detail by using finite that slots which are significantly wider than the current element analysis. slots result in a significant decrease in junction stress. To determine the effect of the slot dimensions on junc- Using finite element analysis, the slot design of the tion stress, an existing coke drum with a slotted skirt skirt support structure can be efficiently and accurately is modelled and solved using finite element analysis. optimized. Properties of base material SA387 steel and clad ma- terial TP410S stainless steel are used for the determi- References nation of stresses (Yan et al.). Temperature-dependent Cheng, D. H. and N. A. Weil. “The Junction Problem of Bilinear kinematic hardening plasticity model is used Solid-Slotted Cylindrical Shells.” Journal of Applied to capture the deformation and stress/strain of the Mechanics (1960): 343-349. Document. structure under cyclic thermal-mechanical loading.. A Yan Z. et al., Statistical method for the fatigue life esti- convection boundary condition is applied to the fac- mation of coke drums. Eng Fail Anal (2014), http:// es of the model corresponding to the interior of the dx.doi.org/10.1016/j.engfailanal.2014.11.007 drum. The ambient temperature and convection co- Xia, Z., Ju, F., and Plessis, P. D., 2010, “Heat transfer efficient are then ramped to simulate two full cycles and stress analysis of coke drum for a complete of thermal-mechanical loading (Xia et al.). The outer operating cycle.” Journal of Pressure Vessel Technol- surfaces of the model are fully insulated, as is the case ogy, 132: 051205 142 Talk Topic C 5: Cyclic deformation behavior, crack initiation & crack growth of metals Numerical and experimental analysis of the influence of pro- cess parameters on the damage of hot rolling rolls Luiz Gustavo Del Bianchi da Silva Lima1, Alexandre Gonçalves2, Ana Paola Villalva Braga2, Izabel Fernanda Machado1, Roberto Martins de Souza1, Mário Boccalini Jr.2 1 Surface Phenomena Laboratory, Department of Mechanical Engineering, Polytechnic School, University of São Paulo, Brazil 2 Institute for Technological Research, São Paulo, Brazil Thermal fatigue is one of the main phenomena that In this work, the methodology described above was ap- lead to loss of rolling quality or failure in hot rolling plied. A reduced scale mill was assembled, and several rolls, mainly in the roughing stands but also in finish- AISI 1045 slabs were hot-rolled by a pair of AISI H13 ing passes (Stevens et al, 1971). This phenomenon is rolls. Rolling was performed in an alternate fashion - 5 caused by the heating of the roll surface when in con- passes for slab, each pass with a thickness reduction tact with the slab, followed by the cooling imposed of 15% - and cooling was applied to the surface of in this surface to keep its temperature under control the rolls after each pass. The rolls were instrumented during successive rolling passes. The amount and rate to retrieve roll temperature and rolling forces in each of damage is influenced by several variables of the hot pass. Additionally, the roll was unmounted periodical- rolling process, such as slab temperatures, thickness ly for wear and thermal fatigue crack inspection. The reduction, roll and slab velocities and many others. In data obtained in this mill was analyzed and then used fact, such dependency on process variables makes the to validate and calibrate a three-dimensional numeri- study of thermal fatigue a complex subject, which in- cal model of the process, developed in finite-element clude the difficulty in instrumentating an actual work- commercial package ABAQUS/Explicit. Once the model ing roll and the inherent cost of periodically removing was validated, different scenarios could be studied, by it from operation to conduct surface inspection. changing three rolling parameters: initial temperature The main alternatives to actual roll instrumentation distribution in the slab, thickness reduction at each and inspection are: (i) To work in a reduced scale mill pass and roll cooling regime. The results for each group and (ii) to study the subject using numerical tools. Both of scenarios were then compared, in terms of axial scenarios have limited scope when uncoupled, since and circunferential stresses in the roll, which are the reduced scale models are costly and time-consuming, main parameters that control thermal fatigue cracking while numerical modeling needs calibration and vali- throughout the rolling process. dation from actual processes. Thus, a more powerful strategy is to couple both approaches – that is, to per- References form a limited number of reduced scale experiments Mercado-Solis, R.D., Talamantes-Silva, J., Beynon, J.H., and use the results to calibrate and validate a wider Hernandez-Rodriguez, M.A.L. (2007): Modelling series of numerical models. This strategy was applied surface thermal damage to hot mill rolls – Wear, successfully by other authors (e.g. Tseng et al, 1989; 263: 1560-1567. Mercado-Solis et al, 2007), although these works either Stevens, P.G., Ivens, K.P., Harper, P. (1971): Increasing focus only in general subjects of hot rolling or approach work-roll life by improved roll-cooling practice – the rolling process and the thermal fatigue involved in Journal of The Iron and Steel Institute, 209: 1-11. a simplified manner. Tseng, A.A., Lin, F.H., Gunderia, A.S., Ni, D.S. (1989): Roll cooling and its relationship to roll life – Metal- lurgical Transactions, 20A: 2306-2320. 143 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic C 6: Cyclic deformation behavior, crack initiation & crack growth of metals 144 Talks Topic C 6: Cyclic deformation behavior, crack initiation & crack growth of metals Rolling Contact Fatigue Strength of Ceramic Coated Steel La- ser-Quenched after Coating Process Hirotaka Tanabe1, Yuki Nakamura2, Yui Izumi1, Tohru Takamatsu1 1The University of Shiga Prefecture, Hassaka, Hikone, Japan 2Engineering Graduate School, The University of Shiga Prefecture, Hassaka, Hikone, Japan In our previous studies, a new surface modification ser quenching. The process time, in which the ceramic method by combination of ceramic coating and laser coating of the specimen was exposed to an elevated heat treatment, “laser quenching after coating”, was temperature, of the furnace quenching was much lon- developed. In this method, a steel substrate is first ger than that of laser quenching. coated with a ceramic thin film by PVD or CVD method, The effects of laser power on the delamination initia- and then the substrate is quenched by laser irradiation tion life of laser quenched specimens were investigat- to the ceramic coated surface. By applying this meth- ed. From 800W to 880W, the delamination initiation od, it was possible to improve the adhesive strength life was increased with laser power. The delamination and substrate hardness of ceramic coated steels effec- initiation life of the specimen laser-quenched at 900W tively without compromising the film hardness and the was quite short. A good correlation was recognized be- toughness. From these results, it was considered that tween the delamination initiation life and the adhesive the raceway of ball bearing would be one of the good strength of CrAlN film of laser-quenched specimens. applications of this method. It is considered that laser quenching after coating with In this study, to investigate the effects of “laser quench- the suitable laser power could be an effective way to ing after coating” on the rolling contact fatigue strength improve the delamination initiation life and to reduce of ceramic coated steels, the thrust type rolling contact the delamination growth rate under rolling contact fa- fatigue tests were carried out for ceramic coated steels tigue. processed by laser quenching after coating. For the substrate, carbon tool steel JIS-SK105 was used. CrAlN References film was coated on this substrate by arc ion plating. The H. Tanabe, et al. (2014): Effects of laser heat treat- film thickness was 2.5µm. For laser quenching process, ment on mechanical properties of ceramic coated a high power diode laser system was used. Laser power steels Part 1 – Laser irradiation conditions and me- was changed from 800W to 900W. For the comparison, chanical properties of ceramic coated steels, Ma- the rolling contact fatigue tests were also carried out terials Research Innovations, 18, S12 – S16, Maney for the specimens furnace-quenched after coating. Publishing. The delamination initiation life of the laser quenched H. Tanabe, et al. (2014): Effects of laser heat treat- specimens and the furnace quenched specimens were ment on mechanical properties of ceramic coated compared. The delamination initiation life of the la- steels Part 2 – Fracture strength of laser heat treat- ser quenched specimens was longer than that of the ed ceramic thin film, Materials Research Innova- furnace quenched specimens. After the initiation, the tions, 18, S17 – S21, Maney Publishing. delamination of the furnace quenched specimen grew much faster than that of laser quenched specimen. Acknowledgements These reasons could be explained by the difference of This work was supported by JSPS Grants-in-Aid for Sci- the process time of the furnace quenching and the la- entific Research (C) (No. 25420025). Crack propagation behavior in titanium alloy under com- bined axial-torsional cyclic loading modes Toshihiko Hoshide1, Tetsuya Tokuhara2, Masashi Nagaoka2 1 Department of Energy Conversion Science, Kyoto University, Kyoto, Japan 2 Graduate School of Energy Science, Kyoto University, Kyoto, Japan Titanium (Ti) alloys are expected to be a candidate of state which is anticipated being generated in actual light materials having higher strength. To guarantee components. long-term integrities of Ti alloy components in their In this work, the behavior of fatigue cracks in Ti alloy services, it is important to clarify the behavior of fa- under biaxial stress state was investigated by using tigue crack propagation in Ti alloy under biaxial stress thin tubular specimens of Ti-6Al-4V titanium alloy. 145 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Force-controlled fatigue tests were executed under thin-walled tubular specimens with inclined cracks. axial, torsional and combined axial-torsional loading The range of J-integral was estimated by using the modes. Fatigue tests in the aforementioned three developed procedure, and correlated with the crack loading modes were conducted under a stress ratio R growth rate. The crack growth rate in the Ti alloy under of -1 or -1.2 (especially in axial loading mode), while all testing conditions was almost uniquely expressed by tests under axial and torsional loading modes were a power function of J-integral range, independently of also carried out under R = 0. By interrupting a fatigue testing condition. test several times, the behavior of fatigue cracks was Furthermore, in the correlation with the crack growth observed by using a plastic replication technique, and rate, availabilities of J-integral range based parame- deformation in a cracked tube was also examined by ters, i.e., J-integral range divided by yield strength or monitoring crack-center opening displacement (CCOD) Young’s modulus, were also discussed. versus force curves. Fatigue crack propagation rate is quantitatively ana- References lyzed in the framework of fracture mechanics, and usu- Paris, P.C., Gomez, R.E. & Anderson, W.E. (1961): A ally by using stress intensity factor (Paris 1961, ASTM rational analytic theory of fatigue, The Trend in En- E-647 2007). It was seen that relations between crack gineering, Vol. 13, No. 1, 9-14. propagation rate and stress intensity factor range in ASTM Designation E647-05 (2007): Standard test eight distinct testing conditions were different from method for measurement of fatigue crack growth each other. Effective stress intensity factor was evalu- rates, Annual Book of ASTM Standards, Vol. 03.01. ated by taking account of crack closure (Elber 1970), Elber, W. (1970): Fatigue crack closure under cyclic and a crack opening point was determined from CCOD tension, Eng. Fract. Mech., 2, 37-45. vs. force curve. The effective stress intensity factor was Rice, R.J., Paris, P.C., & Merkle, J.G. (1973): Some correlated with crack propagation rate, and almost further results of J-Integral analysis and estimates, good correlation was found. However, the propaga- ASTM STP 536, 231-245. tion rate under large scale yielding state shifted toward Hoshide, T., Yamada A. & Tanaka, K. (1983): Elas- higher rate region compared with the crack growth re- tic-plastic finite-element analysis of cracked plate lation under small scale yielding state. A simple meth- under biaxial stress and its application to fatigue od of J-integral evaluation (Rice, Paris & Merkle 1973, crack propagation, J. Soc. Mater. Sci., Japan, Hoshide, Yamada & Tanaka 1983) was developed for 32(356), 528-534. The AA2124/SiC metal matrix composites under fatigue, creep and monotonic loading conditions Agnieszka Rutecka, Paweł Grzywna, Lech Dietrich Institute of Fundamental Technological Research, Polish Academy of Sciences (IPPT PAN), Warsaw, Poland Metal matrix composites (MMCs) are well known as The first aim of the investigations was to obtain mate- materials lighter and simultaneously more durable rials parameters such as elastic modulus, yield stress, than traditional ones [1-3]. Recently they are more ultimate tensile strength and strain to failure. Moreo- often used in aerospace and automotive industries. ver, during tensile tests several unloadings were per- Engine components such as pistons, connecting rods, formed to evaluate degradation of elastic modulus of brake callipers and cylinder liners as well as chassis the MMCs during tension. Thus, damage evolution of components can be manufactured from the MMCs. the MMCs under tensile conditions was obtained. Ad- During exploitation they are often subjected to fatigue, ditionally, the unloadings for engineering strain equal creep or monotonic loadings. Therefore AA2124/SiC to 1, 2, 3 and 4% were repeated twice and two hystere- MMCs were investigated under aforementioned con- sis loops for each aforementioned unloading strain val- ditions. ues were obtained. It is worth to notice that the widths During the MMCs production aluminium alloy AA2124 of the second loops for each unloading were smaller powders (matrix) and SiC particles (reinforcement) and the elastic moduli during unloading were higher in were mixed and subjected to hot isostatic compaction, comparison to the same parameters for the first loops. forging and CWQ T6 heat treatment. The MMCs were Thus, strain hardening was observed for the MMCs reinforced with 17 and 25% of SiC. The size of SiC parti- from the first to the second cycles. cles was equal to 3 µm. Force controlled fatigue tests were carried out at ambi- Strain controlled tensile tests were performed at am- ent temperature. Sine shape symmetric tension-com- bient temperature with strain rate equal to 2·10-4 1/s. pression cycles were applied with frequency equal to 146 Talks Topic C 6: Cyclic deformation behavior, crack initiation & crack growth of metals 10 Hz. Constant stress amplitudes ranged from 300 to calculated for each specimen. They obey Norton’s law 350 MPa for AA2124+17%SiC and from 330 to 380 MPa of secondary creep. for AA2124+25%SiC. Both MMCs under aforemen- tioned stress amplitudes behaved similarly. Hysteresis Acknowledgements loops width enlarged significantly during compression The results presented in this abstract have been ob- and first cycles, and decreased during subsequent cy- tained within the project “KosDeKom” (project no. cles. Thus, inelastic strain amplitudes obtained high 1576/B/T02/2011/40) with the National Science values at the beginning of tests and decreased during Center, Poland. subsequent cycles, which indicated strain hardening. Mean inelastic strain remained negative during fatigue References tests. Clyne, T.W. &. Withers, P.J. (2003): An introduction Tensile creep tests under constant loading were to Metal Matrix Composites, Cambridge University performed at 300⁰C. The material invasigated was Press. AA2124+17%SiC. The MMC subjected to stress equal Chawla N. &. Shen Y.L. (2001): Mechanical Behavior of to 50 MPa did not reach tertiary creep and the test was Particle Reinforced Metal Matrix Composites, Ad- stopped after about 1200 hours. Two specimens sub- vanced Engineering Materials, 3, No. 6; 357-370. jected to stress equal to 55 MPa reached tertiary creep Rutecka, A., Kowalewski, Z.L., Pietrzak, K., Dietrich, L., after about 200 hours while a specimen under stress Makowska, K., Woźniak, J., Kostecki, M., Bochniak, equal to 60 MPa (with 39 MPa preloading) reached ter- W., Olszyna, A. (2011): Damage development of Al/ tiary creep after about 2 hours. Hence, small range of SiC metal matrix composite under fatigue, creep stress values between long-term and short-term creep and monotonic loading conditions, Procedia Engi- was observed. Additionally, minimum creep rates were neering, 10, 1420-1425. Fatigue crack growth behavior of Ti-6Al-4V ELI alloy under constant amplitude loading with different single overloads Chuanyong Chen1, Duyi Ye1, Xumin Hu1, Jianzhong Liu2, Lina Zhang2 1Institute for Process Equipments, Zhejiang University, Hangzhou, China 2Division of Mechanical Properties, Beijing Institute of Aeronautical Materials, Beijing, China Aviation components widely made of titanium alloy are rate showed that different degrees of retardation usually suffered to variable amplitude loading in the effects occurred after all single overloads except single process of service. Many researches have been carried compressive overload. The intensity of retardation out attempting to obtain clear crack propagation effect diminished dramatically with the decreasing behavior under variable amplitude loading to predict of overload ratios and almost disappeared at the the residual life of a component with detectable cracks minimum overload ratio Rol=1.375. There did not accurately (Skorupa 1998), but few these investigations appear pronounced acceleration effect in the single for titanium alloy especially for the Ti-6Al-4V ELI were compressive overload condition. Transient acceleration conducted . phenomena immediately after single overloads were The aim of this study is to investigate effects of also obtained in some situations. different single overloads (i.e., single tensile overload, Quite a lot of models were proposed to interpreter single compressive overload, tensile-compressive over- crack growth rates under variable amplitude loading load and compressive-tensile overload) on the fatigue including yield zone models and crack closure models crack growth behavior and inTi-6Al-4V ELI alloys. The (Schijve 2008). In this study, the mechanism of overload crack growth rate under constant amplitude loading effect was discussed based on the crack propagation and that interspersed with different single overloads behavior and crack profiles evolution. Here, it was at the same crack length were examined systemati- thought that the interaction effects of the plastic zone cally in laboratory environment. Three overload ratios containing compressive residual stress ahead of crack were applied for each overload form, thus a total of tip and the crack closure in crack wake played a dom- 12 crack propagation tests were conducted using M(T) inated role in influencing the crack growth behavior specimens according to ASTM E647-08. Fractography under variable amplitude loading. The crack profile and crack morphology such as branching, deflection would be changed dramatically with the arising of large and blunting were inspected using SEM and optical overload and there were interactions between crack microscope respectively. The measurements of crack growth behavior after overload and these crack profile 147 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 changes. The transient acceleration after overloads ing—a literature review. Part I: empirical trends. was due to the combination of lack of closure induced Fatigue & Fracture of Engineering Materials & Struc- by crack blunting and more slip bands and secondary tures, 21(8), 987-1006. cracks at crack tip. Schijve, J. (2008): Interaction models for prediction of fatigue crack growth under VA loading. – In: Fatigue References of Structures and Materials(pp.353-361). Springer Skorupa, M. (1998). Load interaction effects during Netherlands. fatigue crack growth under variable amplitude load- Prestrain memory on subsequent cyclic behavior of FCC metallic materials presenting different dislocation slip tendencies Gael Marnier, Clement Keller, Lakdhar Taleb Groupe de Physique des Matériaux, INSA Rouen, Université de Rouen, St. Etienne du Rouvray, France The forming process of metallic industrial parts often ing stages of each material and the cyclic ones were involves steps of strong plastic strains which are sus- selected in order to study the influence of preharden- ceptible to modify subsequent fatigue properties (fa- ing due to each of the typical dislocations structure in tigue life, stress-strain level …) in service compared to fatigue (i.e. veins, persistent slip bands and cells). All the well-known cylic behavior of the equivalent fully tests have been carried out under tension-compres- annealed material. Such modification, henceforth sion at room temperature. called “memory effect“, is related to the prehardening The CSSCs of prestrained specimens and virgin ones inherent to predeformation and has been widely stud- were compared. Firstly, the existence of a prestrain ied during the past decades. Nonetheless, the deep threshold implying a memory effect was thus highlight- understanding of this phenomenon is still a work in ed. Then, cyclic plastic strain thresholds requiered to progress. erase prestrain memories were also identified. Finally, In the case of FCC metallic materials, several research- stress partition has been applied on fatigue tests and ers argued about the influence of dislocations slip pla- it results that memory effect is mainly related to the narity. On one hand, wavy slip materials such as pure memory of the internal stress value inherited from copper have been presented as independent, or at prestrain. least weakly dependent, to prestrain history [1,2]. On In the past, memory effect was reported to be a con- the other hand, investigated purely planar slip materi- sequence of the stability of the prehardening disloca- als were reported as strongly sensible to memory ef- tions structures [1-3] and this statement is also con- fect [1,3]. Anyway, this prestrain history dependence firmed here by the role of internal stress in memory. deserves further discussion and this work intends to As a consequence, TEM investigations were carried out cartography the domain of existence of memory effect on each material with the objective of discussing the as a function of stacking fault energy by studying three evolution of the fraction of grains still presenting the different materials: pure Copper as a wavy slip materi- prestrain structure after different amount of cycling. al, Nickel-Chromium alloy as a mainly planar slip mate- rial, and a 316L stainless steel which presents a mixed References behavior. [1] C.E. Feltner and C. Laird, Acta Met., 15 (1967), In order to do so, Cyclic Stress-Strain Curves (CSSCs) 1612-1653. were acquired for all materials by incremental step [2] H.-J. Christ, G. Hoffmann, O. Öttinger, Mater. Sci. tests in total strain control. Both monotonic and cyclic Eng. A201 (1995), 1–12. prestrains were used for this study. The tensile pre- [3] K. Schoeler, H.-J. Christ, Int. J. of Fatigue 23 (2001), strains were chosen accordingly to the strain-harden- 767-775. 148 Talks Topic C 7: Cyclic deformation behavior, crack initiation & crack growth of metals Talks Topic C 7: Cyclic deformation behavior, crack initiation & crack growth of metals 149 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 The effects of periodic overloads and high/low loading blocks on fatigue crack growth of aluminum alloy Haifeng Xu1, Duyi Ye1, Lei Xiao1, Jianzhong Liu2, Lina Zhang2 1Institute for Process Equipments, Zhejiang University, Hangzhou, China 2Division of Mechanical Properties, Beijing Institute of Aeronautical Materials, Beijing, China Aluminum alloy is widely used in aircraft manufacturing The same phenomenon was found in high/low and for its lightweight, but working in extreme conditions. low/high loading tests, while the high ratio load (R As an example, the tension wing skin which is made = 1.375) is smaller, but the crack propagation rate is of aluminum alloy subject to variation of loads in its equal to 0 after a high ratio loading block. lifetime and is well recognized as a fatigue critical part At last, fracture surfaces were examined with stereomi- (Schijve 2008). Therefore it is important to figure out croscope, black spots have been found between shear the generalization of damage tolerance to variable am- lips of a fatigue crack where tensile overload or high plitude fatigue (Romeiro 2009). ratio loads took place. That indicates severe friction or This paper presents an analysis of fatigue crack growth squeeze exists at the front of crack tip after overload on M(T) specimens made of 2524-T3 aluminum alloy. or high loads that cause black fretting products. The The specimens were subjected to repeated blocks of results have shown that the retardation effects in fa- cycles made up of a single overload(i.e. tensile, com- tigue crack growth are closely related to the residual pressive, tensile-compressive or compressive-tensile) stress around crack tip and the plasticity induced crack or a block (10000 cycles) of high ratio loads separat- closure, and the later could play the dominated roles in ed by a number (10000 or 20000 cycles) of baseline influencing the crack growth behavior under variable cycles. Crack opening displacement (COD) extensome- amplitude loading. ter and optical microscope were used to measure the crack length and investigate the crack profiles respec- References tively. The retardation and delay retardation have been Schijve, J. (2008): Different types of loads on a struc- found after overloads of tensile, tensile-compressive ture in service. – In: Fatigue of Structures and Mate- and compressive-tensile, but acceleration effect were rials(pp.261-267). Springer Netherlands. found after compressive overloads. An interesting phe- Romeiro, F. De Freitas, M, De Fonte. (2009)Fatigue nomenon was that, the stable crack propagation rate crack growth with overloads/underloads: Interac- was reduced gradually after every single tensile over- tion effects and surface roughness. – In: Internation- load (Rol = 1.685), and nearly stopped to grow under al Journal of Fatigue, 31(11-12), 1889-1894. baseline cycles after several single tensile overloads. Multiaxial fatigue damage in fibrous composites: an ap- proach based on micromechanical crack growth Roberto Brighenti, Andrea Carpinteri, Daniela Scorza Dept. of Civil-Environmental Engng & Architecture, Univ. of Parma, Parma, Italy Fibre reinforced composite elements are frequently lows to easily describe their behaviour under fatigue used in severe structural applications involving repeat- loading. ed loading responsible for progressive deterioration Damage degradation can thus be applied to the matrix and damage. Fibre reinforced composites are mul- mechanical charactersitics, and – by assuming a 3-D tiphase materials characterized by complex mechanical mixed Mode fracture description of the fibre-matrix phenomena due to the different mechanical properties detachment – fracture mechanics and crack growth of the costituents and their reciprocal interactions [1-2]. rate concepts can be conveniently used to determine In presence of fatigue loading, the safety assessment the progressive fibre debonding responsible for the of fibrous composites requires to describe and quanti- loss of effectiveness of the reinforcing phase [3]. fy the degradation phenomena taking place mainly in In the present paper a micromechanical model for the matrix material and at the fibre-matrix interface. unidirectional or random distributed fibre reinforced The possibility to apply damage mechanics and frac- elements is developed and applied to the evaluation ture mechanics concepts to this class of peoblems al- of the fatigue behaviour under unixial and multiaxial 150 Talks Topic C 7: Cyclic deformation behavior, crack initiation & crack growth of metals fatigue stress states. Damage in the bulk material is expressed through the SIFs related to the radial and ax- accounted for through a Wöhler based damage pa- ial stress field of the fibre (Fig. 1). rameter, D (σ *c , R *, N ) , suitable for the reduction of The above degrading effects are finally taken into ac- a generic mechanical property of the material Pm (N ) count in a proper homogenisation procedure in order with the number of loading cycles: to determine the averaged macroscopic properties of [ ] one equivalent locally homogeneous material that can Pm (N ) = P * *m,0 ⋅ 1- Dc (σ , R , N ) be simply used in practical FE numerical analyses of On the other hand the 3D crack, representing the fibre- real structural components. matrix detached region (Fig. 1), can be assumed to Some applications related to the fatigue behavior of polymeric fibre-reinforced composite are presented present a crack growth velocity vcg given by: for both uniaxial as well as biaxial in phase and out of v dl / dN C K m , K K K phase fatigue stresses; the obtained results are com-icg = = i ⋅D i D th < D i ≤ IC pared with experimental data found in the literature. where DKi represents the equivalent SIF range at the crack front interface region: References [1] Cheng, QG. (2012) Fiber Reinforced Composites. Nova Science Publishers, Inc., Hauppauge, NY.  K 2 2 (σ ∞ ) + [K (σ ∞ ) + K (σ ∞ )] σ ∞ > 0 [2] Brighenti, R, Carpinteri A, Scorza D. (2012) A com-Ki =  I r I r I z r  K (σ ∞ ) σ ∞ ≤ 0 putational approach to evaluate the mechanical  I z r influence of fibres on brittle-matrix composite ma- terials. Comput. Mat. Sci. 64: 212-215. [3] Brighenti, R., Carpinteri, A., Scorza, D. (2013) Frac- ture mechanics approach for partially debonded cylindrical fibre. Comp Part B 53: 169–178. Fig. 1. Debonded extremity (3D cylindrical crack) of a fibre ∞ ∞ under remote radial (σ r ) and axial (σ z ) stresses. Predicting the fatigue life at crack initiation in cruciform welded joints by using the effective cyclic J-integral (∆Jeff) Desire Tchoffo Ngoula, Heinz Thomas Beier, Michael Vormwald Institute of Steel Construction and Materials Mechanics, Technische Universität Darmstadt, Germany In this paper, recent results of the Institute of Steel work numerical analyses using two dimensional plane Construction and Materials Mechanics (IFSW) of TU strain models and elastic-plastic materials behaviour Darmstadt inside a project called IBESS („Integrale of steel are performed in order to predict the fatigue Bruchmechanische Ermittlung der Schwingfestigkeit life at crack initiation of cruciform welded joints. Fa- von Schweißverbindungen“) are presented. The aim tigue crack growth analyses are performed by using of IBESS is the fracture mechanics based simulation the node release technique together with the finite of Wöhler curves (S-N curves) in welded joints, see element program Abaqus. The element size used in [4]. IBESS is divided into 8 subprojects and the IFSW is the crack domain is about 0.025 mm which is small working on the subproject titled: “Modelling of fatigue comparing to the Dugdale’s plastic zone size . is com- crack growth in welded joints under consideration of monly used as reference. The plasticity-induced crack the transient plastic deformation behaviour.” In this closure (see, [1]) effects are taken into account by de- 151 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 termining the time at which the crack remains close/ open and by using the effective cyclic J-integral (∆Jeff) References instead of the cyclic J-integral (∆J) in a relation similar E. Herz, O. Hertel, M. Vormwald: Numerical simulation to the Paris equation . For this purpose, a python code of plasticity induced fatigue crack closure for aut- was written in order to determine ∆Jeff at every crack ofrettaged intersecting holes. Engineering Fracture length phase. It is also shown in this contribution that Mechanics, 78, S. 559-572, 2011 the plasticity-induced crack closure and consequently R. Döring, J. Hoffmeyer, T. Seeger, M. Vormwald: A ∆Jeff depend on the elastic-plastic material law to be Plasticity Model for Calculating Stress-Strain Se- used. This is done by using the Döring’s (see, [2]) and quences Under Multiaxial Nonproportional Cyclic the Chaboche’s material models. The predicted fatigue Loading. Computational Materials Science, 28, S. lives are compared with experimental data and a good 587-596, 2003 accordance between both results was achieved. Due R. Thumser, J.W. Bergmann, M. Vormwald: Residual to the importance of residual stresses in the integrity stress fields and fatigue analysis of autofrettaged assessment of welded joints, their influence on ∆Jeff as parts. International Journal of Pressure Vessels and well as on the fatigue life during short crack growth is Piping, 79, S 113-117, 2002 investigated. Specific structure calculations are used U. Zerbst: Assessment of welded joints by fracture in order to introduce the measured welding residual mechanics. IBESS – The development of a proce- stress field in finite element model, see [5]. The cal- dure. Proceedings of the 4th Symposium on Structur- culated residual stress field match the measured one al Durability in Darmstadt, ISBN 978-3-8396-0734-3, especially in the weld notch area. Results show that a S. 49-65, 2014 tensile residual stress field is unfavourable to fatigue H. Th. Beier, B. Schork, J. Bernhard, D. Tchoffo Ngoula, life while a compressive residual stress field is favoura- T. Melz, M. Oechsner, M. Vormwald: Simulation of ble to fatigue life. Furthermore, it is shown that calcu- fatigue crack growth in welded joints. Proceedings lations using the initial welding residual stress field and of the 4th Symposium on Structural Durability in those using the redistributed residual stress field lead Darmstadt, ISBN 978-3-8396-0734-3, S. 1-17, 2014 only to slightly different results in fatigue life. Fatigue behavior of Al/Steel dissimilar resistance spot welds fabricated using Al-Mg insert film Ren Ito, Ishak Ibrahim, Yoshihiko Uematsu, Toshifumi Kakiuchi, Yun Kyyoul, Chihiro Matsuda Gifu University, Japan Recently, reducing weight is one of very important topics was applied for the joining between Al and steel using in automobile industries to improve fuel efficiency. Al-Mg insert film. The film is aiming at the reduction Conventional steels are still widely used as automobile of electric resistance between Al and steel sheets. structural components because of its advantages such Al-Mg insert film exhibits lower melting point than as lower price and higher strength than aluminum Al alloy. Consequently, melted film at lower voltage (Al) alloys, recyclability and so on. But the major would fill the gap between two sheets and reduce the disadvantage is the heavier weigh than Al alloys. Thus, electric resistance, resulting in the effective joining at it is important to develop joining method between steel lower voltage. Subsequently, lap-shear fatigue tests and Al to use steel for load-bearing parts and Al for the had been conducted to evaluate fatigue strength and others. For example, Japanese automobile company figure out fatigue fracture mechanism. MAZDA has applied a friction stir spot welding (FSSW) Materials used are Type304 stainless steel and technique to join steel and aluminum alloy to reduce A6061-T6 sheets with the thickness of 2mm. Thin Al- the weight of components. But the processing time of Mg file was inserted between two sheets and lap-shear FSSW is longer than that of conventional resistance type specimen was fabricated by an RSW technique. spot welding (RSW), and they have to integrate new Fatigue tests were conducted using electro-hydraulic and expensive FSSW equipment into their production fatigue testing machine at a load ratio, R, of 0.1. The S-N line. If RSW technique could be efficiently used for the diagram revealed that the RSW joints exhibited higher joining between steel and Al, processing time is much lap-shear fatigue strengths than Al/steel dissimilar shorter than FSSW and the current equipment could welds fabricated by an FSSW method. Fatigue fracture be used. Furthermore, applying Al/steel dissimilar modes were dependent on the load levels, where pull- welds to the actual components, it is very important to out fracture occurred at high load levels, shear fracture understand fatigue behavior of joint. In this work, RSW in the nugget at medium load levels, and through- 152 Talks Topic C 7: Cyclic deformation behavior, crack initiation & crack growth of metals thickness fatigue crack propagation in Al sheet at low around the nugget. By lowering the load level, the load levels. initiated crack tended to propagate along the interface, The fractographic analysis revealed that the pull-out resulting in the shear-type fracture. Further decrease fracture occurred due to the crack initiation at the of load level led to the through-thickness crack propa- edge of the nugget followed by the crack propagation gation into Al sheet. High cycle fatigue strength of pure lead Masahiro Endo1, 2, Keiko Morita3, Akira Yasunaga4 1Department of Mechanical Engineering, Fukuoka University, Japan 2Institute of Materials Science and Technology, Fukuoka University, Japan 4Sumitomo Metal Mining Siporex Co., Ltd., Tokyo, Japan Pure lead is a typical hysteretic damping material on the surface of lead had a favorable effect in enhanc- that has a high energy dissipation capability by plastic ing the fatigue life and the fatigue limit (defined at 3 x deformation because of its almost perfect rigid-plastic 107 cycles). Gough and Sopwish (1935) and Snowden behavior with little strain rate dependence. The lead (1964) inferred that fatigue strength in air was influ- damper, which can absorb effectively a large amount enced by the interacting effect between oxygen and cy- of the kinetic energy during an earthquake, has been clic loading. In addition, the tension-compression tests used as a component of a base isolation system of of specimens containing a slit performed in this study modern buildings. revealed that a crack closure induced by grease-coat- In recent year, it has been reported that cracking is ob- ing affected significantly the arrest and deceleration of served on the surface of in-service lead dampers that propagation of a crack emanating from the slit. have never experienced a major earthquake. These cracks could lead to degradation of the damping per- References formance. The principal cause of the cracking is a large Snowden, K.U. (1964): The effect of atmosphere on number of small oscillations due to wind and traffic-in- the fatigue of lead. Acta Metallurgica, 12, 295-303. duced excitations. This problem is exactly a high cycle Morita, K., Takayama, M., Yasunaga, A. (2010): Experi- fatigue (HCF) problem. There are very few research- mental Study on Fatigue Properties of Lead Damper es on the HCF of lead because the strength of lead is for Seismic Isolation System (in Japanese). Summa- smaller than 1% of that of steels. ries of technical papers of Annual Meeting Architec- On the other hand, Snowden (1964), Morita et al. tural Institute of Japan, No. 21168: 335-336 (2010) and Maruta et al. (2013) reported that the fa- Maruta, S., Takayama, M., Morita, K., Yanase, K., tigue life of lead can be increased by a grease-coating. Endo, M. (2013): A study on high cycle fatigue be- However, its effect has yet to be understood quanti- havior in Lead, 9th Int. Conf. Fracture & Strength of tatively and qualitatively. In this study, therefore, to Solids. tackle the underlying problems, we conducted a series Gough, H.J., Sopwish, D.G. (1935): Some further ex- of rotating-bending and tension-compression fatigue periments on atmospheric action in fatigue, J. Inst. tests with pure lead round-bar specimens. To investi- Met. 56, 55-89. gate the influence of a large number of small oscilla- tions, the fatigue tests were conducted mainly in the Acknowledgement HCF regime. The authors greatefully acknowledge the contributions The S-N curves obtained in the rotating-bending fatigue made by Mr. S. Maruta, Master student of Department tests for specimens with and without grease-coating of Mechanical Engineering, Fukuoka University, in the on the surface demonstrated that the grease-coating experimental works. 153 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic C 8: Cyclic deformation behavior, crack initiation & crack growth of metals 154 Talks Topic C 8: Cyclic deformation behavior, crack initiation & crack growth of metals Accuracy improvement of fatigue damage evaluation based on phase analysis of dissipated energy Daiki Shiozawa, Tsuyoshi Inagawa, Atsushi Akai†, Takahide sakagami Department of mechanical engineering, Kobe University, Kobe, Hyogo, Japan †Present affiliation: Toyota Central R&D Labs. INC, Nagakute, Aichi, Japan Fatigue limit estimation based on the dissipated energy The material under test is JIS type 316L austenitic stain- measurement using infrared thermography has been less steel. The cyclic axis loading with a frequency of getting an increasing attention in various industries. 5 Hz was applied to the specimen. In the staircase-like Mechanism of energy dissipation in relation to fatigue stress level test [1], stress amplitude was changed from damage initiation has not been investigated yet. The 200MPa to 280MPa. Dissipated energy on the speci- present author’s group has investigated the mecha- men surface was measured by infrared thermography nism of energy dissipation through AFM observation with a MCT array detector. In the constant stress tests, at crack initiation and dissipated energy investigation the change of dissipated energy and phase difference under shot peening treatment. It was found from these was measured during fatigue test. The stress ratio R results that energy dissipation was related to activity of was set to be -1, -0.8 and -0.5 in both fatigue tests. slip band and estimated fatigue limit is corresponding Dissipated energy at R=-1 increased significantly from to crack initiation stress level of the material. Most of σa=255MPa and phase difference Dq converge to study on dissipated energy has been discussed based around 60 degree for the stress levels where dissipated on the mean temperature rise or irreversible compo- energy shows increase. The experiments were carried nent of heat generation due to energy dissipation. In out at least four times and the results showed good re- this study, phase information of energy dissipation was peatability. The estimated fatigue limit based on dissi- investigated and was applied to the accuracy improve- pated energy coincided with the fatigue limit obtained ment of dissipated energy measurement for fatigue by S-N curve (σw=250MPa). The results at R=-0.8 and damage estimation. -0.5 are similar to that at R=-1. Change of dissipated Temperature rise is observed under compressive stress, energy shows increase from σa=250MPa at R=-0.8, and and temperature fall is observed under tensile stress. σa=240MPa at R=-0.5. The value of phase difference Dq This phenomenon is called as thermoelastic effect. shows constant values of 40 degree at R=-0.8, and 20 Thermoelastic temperature change ΔTE is formulated degree at R=-0.5. by thrmoelastic coefficient k, absolute temperature T, Dissipated energy is small when the applied stress and sum of principal stresses Δσ. is below the fatigue limit, and then phase difference ΔTE = − k T Δσ shows unstable value. On the other hand, phase dif- The thermo-elastic temperature changeΔTE is a revers- ference show a certain value when the applied stress ible phenomenon. However, in the actual case under is above the fatigue limit and the value of dissipated cyclic loading, temperature rise due to irreversible energy show increasing. Unstable value of phase dif- energy dissipation DTD is observed in addition to ther- ference indicates that no slip occurs and measured moelastic temperature change DTE. This kind of heat dissipated energy is in the noise level. The phase infor- generation is considered to be caused by local plastic mation includes the behavior of slip and disslocation. deformation, so it occurs at the maximum tensile stress Therefore, phase information can be used as a filtering and at the maximum compressive stress. Therefore, at dissipated energy measurement. temperature change due to dissipated energy ΔTD can be obtained as double frequency component for the Reference load frequency f . In this study, the phase difference Rosa, G. La, and Risitano, A. (2000): Thermographic Dq between temperature change due to dissipated en- methodology for rapid determination of the fatigue ergy DTD and thermo-elastic temperature changeDTE, limit of materials and mechanical components, In- which was signal with opposite phase for load signal, ternational Journal of Fatigue, Vol.22, pp.65-73. was obtained. DTE and DTD are expressed as following equation; DTE=sin(2p×f×t), DTD=sin(2p×(2f)×t-Dq). 155 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Fatigue damage evaluation of polycrystaline alloy by diffrac- tion contrast tomography using ultra-bright synchrotron ra- diation Yoshikazu Nakai, Daiki Shiozawa, Shoichi Kikuchi, Shota Matsuda, Ryota Nakao Department of Mechanical Engineering, Kobe University, Kobe, Japan A data acquisition technique, aiming at simultaneous tion spot was related to the plastic strain of each grain. reconstruction of three dimensional shape of grains in In the present study, the developed DCT technique is a bulk polycrystalline material, has been proposed by applied to the change of total misorientation of an in- Ludwig et al. [1]. The procedure is termed X-ray dif- dividual crystalographic plane of a specific grain during fraction contrast tomography (DCT), which is similar to fatigue test of a stainless steel sample or a commercial- the conventional X-ray absorption contrast tomogra- ly pure iron sample, where the former is a represent- phy. 　Projected images of grains are obtained using ative of f.c.c. matetial, and the latter, b.c.c. material. the occasionally occurring diffraction contribution to In high cycle fatigue test of the stainless steel, the mis- the X-ray attenuation coefficient for a grain which ful- orientastion of {111} planes increased with number of fils Bragg’s diffraction condition. The three-dimension- cyccles. Among {111} planes, the amount of change al grain shapes are reconstructed from these projec- depended on Schmid factor, i.e., the change was higher tions. The DCT can provide simultaneous access to the for larger Schmid factor. sample’s three dimensional grain arrangement such In low cycle fatigue of the commercially pure iron, the as shapes, locations and crystallographic orientations, misorientation also increased only for {110} planes. together with microstructural features visible in X-ray Among {110} planes, however, the amount of change absorption contrast such as cracks, porosity, inclusions, was not affected by Scmid factor. It indicates that mul- etc. tiple slip should be considered for low cycle fatigue of The authors apply DCT to evaluate dislocation struc- b.c.c. materials. tures in tensile test and low-cycle fatigue test by us- We can discuss about the fatigue crack initiation condi- ing SPring-8 (Super Photon ring – 8 GeV), which is the tion by considering the change of total misorientation brightest synchrotron radiation facility in Japan [2]. of individual clystallographic plane, size of grain where The diffraction spot image spread over a range of suc- crack initiate, and difference of grain orientation be- cessive rotation angle, and only part of the shape of tween neighbor grains. diffracting grain appeared in each projection image. Diffraction spot extend angularly over which individual References diffraction spots are visible, and the spread angle must 1. W. Ludwig, S. Schmidt, E. M. Lauridsen and H. F. give some measure of the orientation spread within Poulsen, Journal of Applied Crystallography, 2008, each grain. This spread could be caused by the mo- 41, 302-309. saicity (i.e. sub-grain misorientation) or the curvature 2. D. Shiozawa, Y. Nakai, R. Miura, and S. Matsuda, Ma- of grain caused by the misorientation, which is related terials Science Forum Vols. 783-786, pp.2359-2364 to a dislocation structure in each grain. We found that (2014). the rotation angle spread for each diffraction/extinc- Dislocation-based modelling of low cycle fatigue in FCC sin- gle and polycrystals Nicolò Grilli1,2, Koenraad G. F. Janssens1, Helena van Swygenhoven2,3 1Laboratory for Nuclear Materials, Nuclear Energy and Safety, Paul Scherrer Institut, Villigen, Switzerland 2NXMM laboratory, IMX, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland 3Material Science and Simulations, NUM/ASQ, Paul Scherrer Institut, Villigen, Switzerland Numerical modelling of cyclic plastic deformation be- Therefore, a multiscale approach is necessary, which haviour of FCC metals is a currently unsolved problem considers the single dislocation properties, such as mo- which involves knowledge of the mechanisms of dis- bility and short-range interactions, but is concurrently location motion. Material damage is determined by capable to describe the collective behaviour occurring microstructural features such as dislocation structures. on a micrometre length scale. We have implemented 156 Talks Topic C 8: Cyclic deformation behavior, crack initiation & crack growth of metals specific dislocation-based constitutive equations for (vein-channel structures) and multiple slip deforma- cyclic fatigue at room temperature, in which several tion (labyrinth and cell structures) are found after 100 dislocation density classes are used as state variables, deformation cycles. The new model is capable to pre- in a crystal plasticity finite element (CPFE) solver. This dict the volume fraction, the characteristic length scale computational method is suitable for introducing arbi- and the orientations of dislocation structures, which trary geometries, boundary conditions and grain orien- is not predicted correctly by existing models (Pontes, tations. Real single crystal specimens and polycrystals 2006). Mechanical properties are also shown: cyclic can thus be modelled. One main novelty we have intro- hardening-softening behaviour has been demonstrat- duced is a dislocation multiplication law based on the ed, together with the strain amplitude dependence of observation that dislocation segments forming locks the model. In this work the DAMASK CPFE code (Rot- have no curvature while this property does not apply ers, 2010) developed at the Max Planck Institute for for dislocations with other orientations (Hochrainer, Iron Research has been used. 2014). A new continuum formulation for cross slip is introduced to take the creation of new Frank-Read References sources and secondary dislocations into account. The S. Catalao et al. Mater. Sci. Eng. A 400-401 (2005) 349- approach used for short-range interactions relies on 352. a Gaussian distribution of interaction strengths to de- J. Pontes et al. Int. J. Plast. 22 (2006) 1486-1505. termine the fraction of mobile dislocations (Catalao, T. Hochrainer et al. J. Mech. Phys. Solids 63 (2014) 2005). We present results from single crystal and poly- 167-178. crystal simulations. Dislocation structures in single slip F. Roters et al. Acta Mater. 58 (2010) 1152-1211. 3D dislocation dynamics simulation of crack shielding and blunting in FCC metals Laurent Korzeczek1,2, Benoit Devincre1, Riccardo Gatti1, Arjen Roos3 1 ONERA/CNRS, Laboratoire d’Etude des Microstructures, Châtillon, France 2 ONERA – The French Aerospace Lab, Châtillon, France 3 Safran Tech Paris-Saclay, France Subjected to low-amplitude cyclic loading, ductile crys- mally activated processes like dislocation cross-slip can talline solids like FCC metals endorse undergo plastic be precisely taken into account. strain localisations, which may lead to the formation To model this complex boundary value problem, the of cracks and subsequent fracture. Experimental evi- Discrete-Continuous Model (DCM) [2] is used to re- dence shows that crack growth and propagation main- produce the interactions of realistic dislocation micro- ly occurs at low stress intensity strongly depends on structures with a short sharp initial crack. Several crack the microstructural behavior and characteristics of the orientations have been studied in a monocrystal and material. Among the mechanisms involved, the inter- detailed analyses of the slip system activity in the plas- actions of the dislocations with the stress concentra- tic zone and the evolution of the shielding and blunt- tion ahead of the crack-tip (plastic zone) seem to play ing mechanisms at the crack tip are presented. These a decisive role. Two main phenomena are of interrest: results are of particular interest for the development • The shielding effect due to the increase or de- of dislocation density based models of crystal plastici- crease of the stress acting on the crack surfaces ty devoted to the complex problem of crack growth in due to the dislocation microstructure developing fatigue. To evaluate the strain energy release around around the crack tip. the crack tip and to quantify the fracture energy for the • The blunting effect induced by the emmision or crack to propagate, a G-theta integral method is tested absorption of dislocation loops at the crack tip on the MDC calculations [3] .Results using the MDC methodology are then com- Modeling these phenomena is a long-standing and pared to Crystal Plasticity Finite Element (CPFEM) sim- complex problem. So far, existing models are essential- ulations using a Meric-Cailletaud law [4] for a copper ly 2D [1] and only few attempts in 3D have been made. monocrystal. Strengths and weaknesses of both ap- 3D dislocation dynamics (DD) simulations are then proaches are discussed. needed to quantitatively investigate the plastic defor- mation restraining crack propagation through shielding References and blunting mechanisms. Only in 3D the influence of [1] W. A. Curtin, V. S. Deshpande, A. Needleman, crystal symmetry, exact slip system activity and ther- E. Van der Giessen, and M.Wallin. Hybrid discrete 157 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 dislocation models for fatigue crack growth. Inter- [3] Destuynder, Ph, M. Djaoua, and S. Lescure. Some national journal of fatigue, 32(9) :1511–1520, Sep remarks on elastic fracture mechanics. Electricite de 2010. France, 92-Clamart, 1981. [2] A. Vattré, B. Devincre, F. Feyel, R. Gatti, S. Groh, O. [4] L. Méric, P. Poubanne, and G. Cailletaud. Single Jamond, and A. Roos. Modelling crystal plasticity crystal modeling for structural calculations : Part 1— by 3d dislocation dynamics and the finite element model presentation. Journal of Engineering Mate- method: The discrete-continuous model revisited. rials and Technology , 113(1) :162–170, 01 1991. Journal of the Mechanics and Physics of Solids, 63(0):491–505, 2014. Analysis of the cyclic plastic response of materials based on the hysteresis loop shape ROMAN PETRÁŠ1,2, JIŘÍ TOBIÁŠ2, JAROSLAV POLÁK1,2 1Institute of Physics of Materials, ASCR, Brno, Czech Republic 2CEITEC, Institute of Physics of Materials, ASCR, Brno, Czech Republic Cyclic plastic response of polycrystalline materials is cyclic strain. The more detailed information about the standardly analyzed using cyclic hardening/ softening sources of hardening/ softening of the material could curves and cyclic stress-strain curve. More information be derived. is however hidden in the hysteresis loop shape. Stand- In two-phase material the initial drop is followed by ard strain controlled low cycle fatigue test program can two peaks provided both phases are deformed during store the selected hysteresis loops during the fatigue cyclic loading. Each peak corresponds to the cyclic plas- life and hysteresis loop shapes could be analysed later. tic deformation of the individual phase. The effective In low cycle fatigue testing of two polycrystalline mate- stress of the harder phase and the probability density rials, austenitic stainles steel and nickel base superallo function of the internal critical stresses in both phases in adddition to the stress and strain amplitudes also can be estimated. full hysteresis loops were recorded The first and the Cyclic loading was performed at room temperature second derivatives of the hysteresis half-loops were and at elevated temperature with two strain rates. The evaluated using digital smoothing procedures. Accord- temperature and strain rate dependence of the plastic ing to the general statistical theory of the hysteresis stress-strain response has been studied and a more loop (Polák 1991) the plot of the second derivative vs. detailed information both on the effective stress and relative strain can be used for the evaluation of the ef- the distribution of the internal critical stresses in indi- fective stress component and the probability density vidual materials was established. function of the internal critical stresses. The second The plot of the second derivative corresponding to derivative of the hysteresis half-loop of a single phase the probability density has been approximated by the polycrystalline material contains initial drop followed Weibull distribution. The parameters of this distribu- by a single peak of the second derivative. The drop cor- tion chracterize the the plastic stress-strain response responds to the relaxation of the effective stress dur- in saturated state. In two phase material both peaks of ing unloading. The effective stress changes only slightly the second derivative could be approximated by Wei- during cyclic plastic straining but the probability den- bul distribution provided the volume fractions of the sity function exibits substantial changes, preferably in phases are approximately the same. the early stage of the fatigue life, i.e. during fatigue hardening/softening. These changes (the height and Reference the position of the peak) were evaluated and discussed Polák, J. (1991): Cyclic plasticity and low cycle fatigue in comparison with the observed localization of the life of metals. Elsevier; Amsterodam. 158 Talks Topic C 9: Cyclic deformation behavior, crack initiation & crack growth of metals Talks Topic C 9: Cyclic deformation behavior, crack initiation & crack growth of metals 159 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 The role of graphite in fatigue crack growth of ductile cast iron under the presence of internal and external hydrogen Takashi Matsuo1, Kosei Yamada2, Hisao Matsunaga3,4,5, Masahiro Endo1, Saburo Matsuoka4 1Department of Mechanical Engineering, Fukuoka University, Japan 2 Graduate school of Kyushu University, Japan 3 Department of Mechanical Engineering, Kyushu University, Japan 4 Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University, Japan 5 International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Japan Two types of fatigue crack growth (FCG) tests of ferri- H-Free ≈ 7. At a lower frequency (e.g. f = 0.01 Hz), the ra- tic-pearlitic ductile cast iron were carried out: (i) FCG tio was drastically decreased and became nearly equiv- test in air using hydrogen-charged specimen to clari- alent to that in air. fy the effect of internal hydrogen and (ii) FCG test in The above peculiar frequency dependence of hydro- 0.7 MPa hydrogen gas using non-charged specimen to gen-induced FCG acceleration is explained by the dif- clarify the effect of external hydrogen. FCG tests were ference in hydrogen distribution ahead of crack tip that performed at a stress ratio of 0.1 and a test frequency influences the degree of slip localization (Matsuo et f ranged from 0.001 Hz to 5 Hz. The hydrogen-charged al. 2010). In the hydrogen-charged specimen, internal specimens were prepared by exposing the specimens hydrogen is attracted to the vicinity of crack tip owing to 100 MPa hydrogen gas at 358 K for 200 hours. The to the stress-induced hydrogen diffusion. On the other ratio of crack growth acceleration due to hydrogen, hand, in the test of non-charged specimen in hydro- (da/dN)H/(da/dN)H-Free, was obtained at the stress in- gen gas, external hydrogen penetrates through surface tensity factor range DK of 20 MPa·m1/2. near crack tip. Consequently, internal hydrogen re- Generally, in BCC steels with a high hydrogen diffusion quires longer time to be concentrated to crack tip zone coefficient, hydrogen-charged specimen is not ade- than external hydrogen. As a result, the frequency at quate for investigation of an effect of internal hydrogen which acceleration ratio peaked out is lower for inter- at very low frequencies (e.g. 0.001 Hz), since internal nal hydrogen than external hydrogen. Further, in the hydrogen rapidly outgases from the specimen during case of external hydrogen at very low frequencies (e.g. the test in air. In contrast, in ductile cast iron, the rate f ≤ 0.01 Hz), hydrogen can be extensively distributed of outgassing is much lower than that of BCC steels ow- over the plastic zone ahead of crack tip. In this situa- ing to the existence of graphites that can store a large tion, slip localization can hardly occur and thereby the amount of hydrogen for a long time (Matsunaga et crack tip would be blunted in a similar way to the non- al. 2013). Therefore, we tested the hydrogen-charged charged specimen tested in air. ductile cast iron in air to investigate the effect of inter- nal hydrogen on FCG in a wide range of frequencies. References In the hydrogen-charged specimen, an accelerated Matsunaga, H., Usuda, T., Yanase, K. and Endo, M. crack growth did not occur at 5 Hz. In the frequen- (2013): Ductility Loss in Ductile Cast Iron with Inter- cy range from 1 to 0.01 Hz, the acceleration ratio in- nal Hydrogen – Metallurgical and Materials Transac- creased with a decrease in f and reached (da/dN)H/ tions A, Vol. 45: 1315-1326. (da/dN)H-Free ≈ 17. At a lower frequency (e.g. f = 0.001 Matsuo, T., Matsuoka, S. and Murakami, Y. (2010): Hz), the ratio was slightly decreased. Fatigue Crack Growth Properties of Quenched and On the other hand, in the tests in hydrogen gas, the Tempered Cr-Mo Steel in 0.7 MPa Hydrogen Gas. – acceleration ratio increased with a decrease in f in the Proceedings of 18th European Conference on Frac- range from 5 to 0.1 Hz, and reached (da/dN)H/(da/dN) ture, Dresden, Germany. 160 Talks Topic C 9: Cyclic deformation behavior, crack initiation & crack growth of metals Shear mode crack propagation along with plastic flow of small area Shuto Fukudome1, Sigeru Hamada2, Masaharu Ueda3, Hiroshi Noguchi2 1Graduate school of Engineering, Kyushu University, Fukuoka, Japan 2Faculty of Engineering, Kyushu University, Fukuoka, Japan 3Yawata R&D Lab., Nippon Steel & Sumitomo Metal Corporation, Kitakyushu, Japan In order to achieve shear mode crack propagation contact machine element and rolled thin film is the which is appeared around the surface of rolling/sliding same in terms of plastic flow. The film was cut to disk contact machine elements along with the plastic flow, shape, the thickness of the film was 30 microns and a test method was developed and the test results are the diameter was three mm in this experiment. For the presented. crack starter, a 600 micron length precrack was intro- Rolling contact fatigue is the damage of rolling/sliding duced on the specimen by FIB (focused ion beam) pro- contact machine elements and the crack exist along cess. By the FIB process, very thin crack can be intro- with the plastic flow. For the applied stress around duced on the specimen and the stress intensity factor the crack, shear stress is considered to be dominant at the crack tip expected to be large. caused by the rolling/sliding contact. Therefore, the Round bar jig and the thin film specimen was bonded author considered that the crack propagated along by quick-drying glue. To make sure that the glue works with the plastic flow by shear mode. Usually the shear properly, flat area was made on the round bar jig. By mode crack is easy to branch to the tensile mode with- applying torque on the round bar jig, shear stress was out compression load on the crack surface. Therefore loaded in the precracked thin film indirectly. Rolling di- the author considered that the plastic flow acts as a rection, precrack direction, and shear loading direction guide to shear mode crack propagation and prevents were all arranged to be parallel. Stress intensity factor the branching. of the crack tip was roughly calculated considering the Some studies were conducted about the shear mode glue layer and the restraint crack deformation by the crack growth and some test methods were proposed. glue. A commercial FEM software was used, and the However, all of the test method needs large (mm scale) value is confirmed to be enough to the crack propa- specimen. The size of the plastic flow layer on the roll- gation. ing/sliding contact machine element surface is a few After the cyclic loading, long shear mode crack has ap- hundred of microns. Therefore, in this study, in order peared on edge of precrack and propagated along with to achieve shear mode crack growth test of such small the plastic flow direction of the thin film. Therefore, area, a test method was developed. the shear mode crack propagation for thin film without Ferritic stainless steel (JIS-SUS430) was adopted in this compression load on the crack surface was succeeded. study. Rolled thin film was used as a specimen. The The authors concluded that crack growth direction was authors assumed the plastic flow of the rolling/sliding guided by plastic flow. A Continuum Damage Mechanics Approach For Prediction of Fatigue Crack Initiation Life Shiva Kumar Chitta, m.m.mayuram Machine Design Section, Department of Mechnical Engineering, Indian Institute of Technology Madras, India Fracture process of ductile materials is still only partly regime(HCF,UHCF) as summarized by Hael Mughrabi unravelled and void growth may well represents the (2013) and it is advantageous to have high crack ini- whole ductile fracture process (under different combi- tiation life. Hence it is important to predict the crack nations of load, time and environment). Fatigue is re- initiation life as accurately as possible. sponsible for up to 80% of the in-service parts failure, The present work is to predict the fatigue crack ini- which occurs in industry. The effective fatigue design, tiation life of Low alloy, SAE 4340 steel,using dam- under ultra-high cycle fatigue is one of the more dif- age models based on Continuum damage mechanics ficult tasks an engineer faces due to involvement of (CDM). Continuum damage mechanics models pro- many factors. In total fatigue life, crack initiation phase posed by S.Dhar et al.(1996) for the ductile damage can have significant percentage, ca 80% or more in de- evolution and for the micro crack initiation are consid- fect-free components and in case of long life fatigue ered for the simulation of ductile damage and failure. 161 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 The work includes both experimental and simulation Salient aspects of the analysis coveing the stress and aspects. The experimental phase includes monotonic plastic strain for micro crack initiation, the critical tensile test and strain controlled fatigue test on cy- damage value and estimationof the fatigue crack initia- lindrical specimens of dimensions as per ASTM E606 tion life are presnted in this paper standard. In the simulation phase, large deformation finite element analysis is carried out using commercial References software Abaqus along with its user material sub rou- Hael Mughrabi(2013): Micro structural fatigue mech- tine UMAT, on cylindrical tensile test specimen. In The anisms: Cyclic slip irreversibility, crack initiation, UMAT, an explicit scheme with Continuum Jacobian is non-linear elastic damage analysis, Int. J. of Fatigue, used for the integration of constitutive models for the 57, 2-8. material behavior in elasto-plastic regime and damage Dhar S, Raju Sethuraman and Dixit P.M.(1996): A Con- evolution law, which are developed based on J2-Incre- tinuum damage mechanics model for void growth mental flow theory along with the concepts of effective and micro crack initiation, Engg. Fracture mechan- stress and hypothesis of strain equivalence. ics, 53(6), 917-928. Generalized critical fatigue crack length for transition from microstructure-driven to mechanics-driven propagation Yasuaki Hamano, Motomichi Koyama, Kaneaki Tsuzaki, Hiroshi Noguchi Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, Fukuoka, Japan The fatigue life is the sum of fatigue crack initiation life tively, we propose a new statistical method. Although and fatigue crack propagation life. Actually, it is known lo depends on many factors as mentioned above, the that the fatigue life is mainly dominated by the fatigue proposed method can give a statistical result with- crack propagation life. Crack growth behavior is divid- out any considerations of the complicated phenom- ed into 3 stages: 1) microstructure-driven small crack ena. The method consists of two steps: I) measuring growth 2) mechanics-driven small crack growth 3) large of crack propagating speed, II) statistically analyzing crack growth. It has been reported that microstruc- the data by using coefficient of variation (CV). The CV ture-driven small crack growth rate is distinctly scat- value decreases with crack growth. A specified crack tered. In contrast, the mechanics-driven small crack length at which the CV value saturates is defined to be which does not follow the Paris Low has less scatter. lo. In this work, strain-controlled tension/compression The long crack which follows the Paris Low propagates fatigue testing was conducted at Δε = 2% and the fre- without scatter, in which the crack growth rate and its quency of 1Hz in air. The surface crack length required associated fatigue crack growth life are predicted pre- for determination of lo was obtained through replica cisely. We name the transition crack length where the technique in certain number of cycles. scatter of da/dN disappears as lo. The length lo may be related to mechanical and microstructural factors, e.g. References average grain size, mean stress, inclusions, crystal ori- Y. Zhao, Q. Gao, J. Wang: Fatigue Fract. Engng. Mater. entations, and grain boundary characteristics. Despite Struct., 22, (1999), 459-467. of the importance of lo, even engineering definition M. Goto: Fatigue Fract. Engng. Mater. Struct., Vol.17, of lo is still unclear. In order to determine lo quantita- No. 6, (1994), 635-649. Fatigue crack growth characteristic under hydrogen atmos- phere in an ultra-low frequency region in Low Carbon and Interstitial Free Steels Yousuke Onishi, Motomichi Koyama, Atsushi NIshimoto, Daisuke Sasaki, Yasuji Oda, Hiroshi Noguchi Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, Fukuoka, Japan Hydrogen has been known to deteriorate mechani- characteristics under the hydrogen environment is es- cal propeties in steels. The understanding mechanical sential in practical uses. In this study, we paid attention 162 Talks Topic C 9: Cyclic deformation behavior, crack initiation & crack growth of metals to frequency dependence of the fatigue crack propaga- plasticity. However, also note that the “disappearance” tion rate under hydrogen environment in low carbon of the hydrogen effect cannot be interpreted by only and interstitial free steels. More specifically, the fatigue the influence of hydrogen distribution. In this work, behavior in an ultra-low frequency region was focused. we suggest that an influence of carbon diffusion to un- At first, we observed the surface fatigue crack prop- derstand this problem. The hydrogen effects assosited agation in the bending fatigue tests of the ultra-low with site competition or a reduction in trap energy of frequency under the hydrogen environment by optical hydrogen by carbon is considered to suppress the HELP microscopy to measure the fatigue crack propagation effect. Moreover, strain age-hardening by carbon at a rate. The fatigue testing was conducted at a 0.7% total crack tip also would decrease in the ultra-low frequen- strain and at hydrogen or nitrogen pressures of 0.18 cy which can provide a sufficient time for the carbon MPa at 40°C. Next we observed fracture surfaces using diffusion. In this report, we discuss the interactions a scanning electron microscope. between hydrogen and carbon and its associated ef- The hydrogen atmosphere was clarified to accelerate fects on fagiue crack propagation rates by using low fatigue crack growth rate compared to that in nitro- carbon and IF steels which do not have a significant gen atmosphere at a frequency of 6 Hz. However, fa- carbon and no solute carbon, respectively to confirm tigue crack propagation rate in nitrogen and hydrogen the influences of the site competition and the strain environments did not have a significant difference at age-hardening. frequency of 0.001Hz. In order to investigate the dis- ppearence of the hydrogen effect, we performed the References detailed observation of a surface crack and the fracture J.P. Hirth: Metall. Trans. A, 11A (1980), 861. surface. In the hydrogen atmophere, a brittle fracture J.E. Costa and A.W. Thompson: Metall. Trans. A, 13A feature including brittle striation was observed partial- (1982), 1315. ly. An important fator supressing the hydrogen effect M. Koyama,E. Akiyama, K. Tsuzakin and D. Raabe: Acta in the low frequency is hydrogen distribution. Namely, Mater., 61 (2013), 4607. a homogenization of hydrogen would diminish the hy- D.G. Enos and J.R. Scully: Metall. Mater. Trans. A, 33A drogen effect in terms of hydrogen-enhanced localized (2002), 1151. Short crack growth kinetics in heat resistant austenitic stain- less steel Sanicro 25 Veronika Mazánová1, Jaroslav Polák1,2, Guocai Chai3,4 1Institute of Physics of Materials, Brno, Czech Republic 2CEITEC, Institute of Physics of Materials, Brno, Czech Republic 3Sandvik Materials Technology, Sandviken, Sweden 4Linköping University, Engineering Materials, Sweden Heat resistant austenitic stainless steel Sanicro 25 has different strain amplitudes. The persistent slip bands been developed for high temperature applications and fatigue cracks developed either intergranularly or mostly in power generation industry. Its resistance to along the grain boundaries were followed in-situ using monotonic and cyclic loading has been studied using optical microscopy and in interrupted tests using scan- creep and low cycle fatigue tests at ambient and ele- ning electron microscopy. vated temperatures (Chai et al. 2013, Polák et al. 2014). The cacks initiate on the surface and soon acquired the The preliminary study of the mechanisms of damage in shape close to a semicircle. Surface crack length pro- cyclic loading (Polák et al. 2014) has revealed apprecia- jected on the plane perpendicular to the loading axis ble localization of the cyclic strain in the persistent slip thus reasonably characterizes the crack topology. Mul- bands and early initiation of fatigue cracks. tiple cracks develop in specimens during elasto-plastic The cyclic slip localization plays an important role also cyclic loading. The crack density of the and its evolu- in the growth of short cracks that often determines the tion during cyclic loading has been evaluated. Individ- low cycle fatigue life of materials. We have therefore ual cracks grow, interact and often link together. The studied both the evolution of the surface relief, the ini- growth rate of the longest cracks is affected by the link- tiation of fatigue cracks, their evolution and kinetics of ing with smaller cracks. The crack length of the three or short crack growth in Sanicro 25 steel at ambient tem- four of the longest cracks in the area of a small notch peratures. The cylindrical specimens with a shallow was plotted vs. number of cycles for different strain notch were cyclically strained in computer controlled amplitudes. The growth of individual cracks could be fatigue testing system with constant strain rate and reasonably well approximated by an exponetial de- 163 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 pendence. Exponetial dependence correspond to the References proportionality of the crack growth rate to the crack Chai G. et al. (2013) Creep and LCF Behaviors of New- length. The parameter of the exponential law, denoted ly Developed Advanced Heat Resistant Austenitic as the crack growth coefficient, depends on the strain Stainless Steel for A-USC. Procedia Engineering, Vol. amplitude or on the saturated plastic strain amplitude. 55: 232-239. The dependence of the crack growth coefficient on the Polák J. et al. (2014) Low cycle fatigue behavior of plastic strain amplitude has benn approximated by the Sanicro 25 steel at room and at elevated tempera- power law. The power low dependence of the crack ture. Mater. Sci. Eng. A615:175–182 growth coefficient corresponds to the Manson-Coffin law provided the cycle number to crack initiation could be neglected. 164 Talks Topic C 10: Cyclic deformation behavior, crack initiation & crack growth of metals Talks Topic C 10: Cyclic deformation behavior, crack initiation & crack growth of metals 165 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Application of area parameter for estimation of thereshold stress intensity factor range ∆Kτth of small shear-mode cracks Saburo Okazaki1, Hisao Matsunaga2, 3, 4, Masahiro Endo4,5 1Graduate School of Kyushu University, Fukuoka, Japan 2Department of Mechanical Engineering, Kyushu University, Fukuoka, Japan 3International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Fukuoka, Japan 4Institute of Materials Science and Technology, Fukuoka University, Japan 5Department of Mechanical Engineering, Fukuoka University, Japan The flaking strength associated with subsurface crack- ing is strongly influenced by the defect size at fracture Kτ = 0.69τ p areas (3) origin (Lewis & Tomkins 2012). Therefore, when per- (for a surface crack) forming a fracture mechanics-based evaluation, the fracture process must be addressed as a small crack Where areai and areas are the square root of the problem. Recently, Matsunaga et al. performed tor- area of an internal and a surface crack, respectively. sional fatigue tests under static compression to meas- Finally, the threshold SIF range for a shear-mode fa- ure the ranges of the threshold stress intensity factor tigue crack, ∆Kτth, can be successfully expressed by us- (SIF), ∆K ing the area parameter. The threshold SIF range ∆Kτth IIth and ∆KIIIth, for the shear-mode growth of small surface cracks between approximately 0.01 and was also found to exhibit a crack size dependence sim- 1 mm in length in a bearing steel (Matsunaga et al ilar to that of mode I cracks (Murakami & Endo 1983) 2011). Consequently, these authors noted a crack size in the small crack size regime. The ΔKτth can be approx- dependence for ∆K and ∆K . imated by the following formulae:IIth IIIth In this study, the ranges of the threshold SIF, ∆K 1/3IIth and ΔKτth = 1.12 ( f + 1.33) ( areai ) (4) ∆KIIIth, for small shear-mode cracks in bearing steel are measured using torsional fatigue testing under static (for an internal crack) compression using aforementioned testing method ΔKτth = 1.26 ( f + 1.33) ( area ) 1/3 s (5) with a newly developed testing machine. The thresh- (for a surface crack) old values are described as a function of the crack size and the crack-face interference. The authors suggest References that the effect of crack-face interference could be Lewis, M.W.J. Tomkins, B. (2012): A fracture mechan- quantified by the fraction of the interfering crack area, ics interpretation of rolling bearing fatigue, proceed- f, which is defined by the following equation: ings of the institution of mechanical engineers, J. area f = crack (1) Eng. Tribol. 226, 389–405. area + area Matsunaga, H. Shomura, N. Muramoto, S. Endo, M. defect crack where area is the area of the interfering crack face (2011): Shear mode threshold for a small fatigue crack and area is the area of the defect with no interfer- crack in a bearing steel, Fatigue. Fract. Eng. M., 34, defect ence. 72-82. In addition, to simplify the evaluation of the shear- Murakami, Y. & Endo, M. (1983): Quantitative evalua- mode threshold, a single parameter, K , is introduced tion of fatigue strength of metals containing various τ to represent the SIF of shear-mode crack as following small defects or cracks, Eng. Fract. Mech. 17, 1–15. fomulae: Kτ = 0.58τ p areai (2) (for an internal crack) 166 Talks Topic C 10: Cyclic deformation behavior, crack initiation & crack growth of metals Fatigue crack initiation near inclusions in Ni superalloys – a SEM based study with high resolution EBSD Jun Jiang1, Jie Yang2, Tiantian Zhang1, Maki Kuwabara1, Fionn Dunne1, Ben Britton1 1Department of Materials, Imperial College London, UK 2Beijing Institute of Aeronautical Materials (BIAM), People’s Republic of China Fatigue lifeing of aeroalloys is an important part of air- ing non-metallic inclusions. High resolution electron craft fleet management and has significant economical backscatter diffraction (HR-EBSD) was used to charac- repecussions for all major aerospace manufacturers. terize the distribution and evolution of geometrically In highly engineered jet engine components micro- necessary dislocation (GND) density, residual stress structure plays a very important role in total fatigue and total dislocation density near a non-metallic inclu- life, prinipally in crack initiation and short crack growth sion. Slip trace anlaysis has been used to characterise which may involve ~1/3 of the life of the component active slip systems and local microstructural sensitivity. (Sangid 2013, Dunne 2014)]. Understanding of this do- This work describes a systematic study of room tem- main requires high fidelity and high resolution charac- perature cyclic deformation processes from cyclic terisation techniques that capture dominent damage hardening, to stabilised cyclic deformation stage, to mechanisms involved in fatigue to inform physically crack formation and propagation stage focussing on motivated modelling efforts. Movement towards ‘suffi- inclusion-matrix interactions. Rather complex defor- cient but not excessive’ design requires significant im- mation structures were directly observed from the first provements with experimentally informed models that few cycles and the patterning did not varies significant- can physically capture approriate deformation mech- ly with increasing number of cycles. Most noticable, a anisms in a timely, efficient and physically motivated clear link was found between crack path and the spa- manner. tially resolved sites of extreme values of residual stress This talk will outline some recent experimental work and GND density. principally using slip trace analysis and high angular resolution electron backscatter diffraction (HR-EBSD). References HR-EBSD is well suited for characterisation at the mi- Britton, T.B., Jiang, J., Karamched, P.S and Wilkinson crostructural lengthscale, capturing residual elastic A.J. (2013): Probing Deformation and Revealing strains with a precision of 1x10-4 and lattice rotations Microstructural Mechanisms with Cross-Correlation with a precision of 1x10-4 and with high spatial resolu- Based, High-Resolution Electron Backscatter Diffrac- tion (~20x60x20nm3) For more information on the HR- tion – in JOM 65:1245-53 EBSD technique, please see a recent review (Britton et Sangid, M.D. (2013): The physics of fatigue crack initia- al 2013). tion – in International Journal of Fatigue 57:58-72 In this study, a series of interrupted thee point bending Dunne, F.P.E. (2014) Fatigue crack nucleation: Mecha- low cycle fatigue tests were carried out on a powder nistic modelling across the legnth scales – in Current metallurgy FHG96 nickel superalloy sample contain- Opinion in Solid State and Materials Science. Non-destructive evaluation of multiple-site small cracks in high-temperature low cycle fatigue of an austenitic stainless steel by using multipoint probe DC potential difference mea- suring system Shio Nakanishi1, Takayuki Suzuki2, Yuji Nakasone1 1 Tokyo University of Science, Japan 2 National Institute of Advanced Industrial Science and Technology, Ibaraki, Japan The develop ment of advanced maintenance techn ol o- improving the depend ability, i.e., the reliability plus gies is a vital issue for extending the fatigue life of en- availabi lity of the facilities. Effective monitori ng tech- ergy conser va tion facilities. Condition-based mainte- nologies are indispens able for non-destructive evalu- nance (CBM) is one of the promising tech nologies for ation of fatigue damage in the CBM. 167 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 In the previous study (Nakanishi 2014), the present measured throughout the whole fatigue process at ad- authors have applied the 4-point probe DC potential equate intervals by the present multipoint probe DC difference method to the non-destructive evaluation potential difference measuring system equipped with of multiple-site small cracks in high-temperature low 32 mini-pin probe. The 4-point mini-pin probe was also cycle fatigue of an austenitic stainless steel JIS SUS316L used for a comparison purpose. The intervals between at 873K in air. The statistical analysis of the potential points of measurement are 0.5 mm in the longitu di nal difference distributions obtained revealed that stan- direction of the specimen and 1.0 mm in the circumfer- dard deviation of normalized potential difference can ential direction. evaluate initiation, growth and coalescence behavior The local potential difference can be regarded to have of multiple-site small cracks in each stage of the fatigue followed normal distributions throughout the fatigue process. processes investigated in this study. The standard The present study has constructed a potential differ- deviation of the potential difference was increased ence measuring system which can measure potential with increasing number of strain cycles at six strain difference distributions on the surface of specimens range levels tested. All the fatigue processes investigat- by scanning fully automatically the specimen sur face ed can be divided into four stages according to the be- of interest. This system consists of the nugget tester havior of cracks; i.e., (1) incubation stage, (2) initiation equipped with a multipoint probe (Denshijiki Industry stage, (3) growth and coalescence stage, and (4) accel- Co., Ltd. 2015), motori zed X-Y-θ stages, the 4-axis stage erated growth stage. The detection of the onset of the controller and a data-collection PC. The probe has as fourth or final stage by the present multipoint probe many as 32 mini-pins arr anged in two-line zigzag along DC potential difference method can non-destructively the longitudinal direction of speci mens to be moni- predict the residual life of fatigue in which multiple-site tored. Each line of the mini-pins has a length of 15 mm small cracks are involved. and are placed 1 mm apart from each other. This probe can collect potential difference data on the whole References reduced-section surface of each one of the present Nakanishi, S. Suzuki, T. & Nakasone, Y. (2014): Non-De- round-bar type specimens within half an hour, about structive Evaluation of Multiple-site Small Cracks in 5 times faster than the previous 4-point probe measur- Low Cycle Fatigue of Austenitic Stainless Steel by ing system (Nakanishi 2014). Four-point Probe DC Potential Difference Method Specimens are round bar type made of an austeni tic – In: Proceedings of The 2nd International Confer- stainless steel JIS SUS316L equivalent of AISI Type 316L. ence on Maintenance Science and Technology: 53- Low cycle fatigue tests were carried out at six applied 54; Kobe, Japan. strain rage levels of up to 1.8% at 873K in air. Local DC Denshijiki Industry Co., Ltd. (2015): http://www. emic- potential difference on each specimen surface was jp.com/english/products/ennt4102/. Crack detection by Sonic-IR method using ultrasonic wave in- putted through water Yui Izumi1, Hirotaka Tanabe1, Tohru Takmatsu1, Takahide Sakagami2 1The University of Shiga Prefecture, Development of Mechanical Systems Engineering, Japan 2Kobe University, Development of Mechanical Engineering, Japan Sonic-IR, which is also called vibro-thermography , is bility of the proposed method for the detection of fa- one of the active thermographic NDT technique. This tigue crack is experimentally investigated. Experimen- method, which is based on the detection of the tem- tal results by the proposed method are compared with perature rise due to frictional heating at the defect fac- conventional sonic-IR technique using ultrasonic horn. es under ultrasonic excitation, has an advantage in the As a results, it was found that crack detection can be detection of closed defects. The method was originally conducted by proposed technique. developed by Henneke (Henneke 1979) and has been advanced and improved (Gleiter 2006, Shepard 2004, References Montanini 2010, Sakagami 2009) more recently. E. G. Henneke II, K. L. Reifsnider & W.W. Stinchcomb: However, in conventional sonic-IR method, to direct- Thermography – An NDI Method for Damage Detec- ly input an acoustic energy from ultrasonic transduc- tion, J.Metal, Vol. 31(9), pp.11-15 er to the test area via ultrasonic horn, which may give A. Gleiter, G. Riegert, Th. Zweschper, R. Degenhardt scratches and deformation in the test object. & G. Busse: Advanced Ultrasound Activated Lock- In this study, we develop a new sonic-IR method using in-Thermography for defect selective depth resolved ultrasonic wave inputted through water, and practica- imaging, Proceedings of SPIE, Vol. 6205, 62051F 168 Talks Topic C 10: Cyclic deformation behavior, crack initiation & crack growth of metals S. M. Shepard, T. Ahmed & J. R. Lhota: Experimental T. Sakagami, R. Katsumata, K. Kuroki, Y. Harada and Considerations in Vibrothermography, Proceedings S. Kubo: Detection of Stress Corrosion Cracking by of SPIE, Vol. 5405, pp.332-335 Sonic-IR Technique, Proceedings of the Seventh R. Montanini, G. L. Rossi & F. Freni: Ultrasound Lock-in International Conference on NDE in Relation to Thermography as a Quantitative Technique for Qual- Structural Integrity for Nuclear and Pressurized ity Control Assessment of Cast Iron Turbocharger Components, pp.1087-1093 Components, Proceedings of 10th International Con- ference on Quantitative Infrared Thermography Low-cycle fatigue Simulation in micro-scale to obtain fatigue behavior of bimodal AL alloys H. Hosseini-Toudeshky, M. Jamalian Department of Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran Fatigue crack initiation and propagation patterns play Finally, the Low-cycle fatigue analysis is applied to the an important role in failures. More than 80% of fail- models through the direct cyclic approach. As a result, ures are caused by fatigue while purely static loading the crack initiation and propagation pattern in mi- rarely occurs. Grain refinement, significantly influenc- cro-scale are predicted and crack growth variation ver- es the resistance of metals and alloys to fatigue crack sus cycle numbers are also obtained. It is shown that initiation and propagation and generally leads to an the predicted results are in good agreement with the increased failure resistance, whereas a deleterious ef- available experimental pattern results. More details fect can be observed on the resistance to fatigue crack will be presented in the full paper. growth. In this study, cryomilled ultra-fine-crystalline Al–Mg References alloy is considered as the material for case study. Elas- Z. Lee, V. Radmilovic, B. Ahn, E. J. Lavernia, and S. R. tic-plastic analyses including crack initiation and prop- Nutt, (2009) “Tensile Deformation and Fracture agation in low-cycle fatigue regime are performed for Mechanism of Bulk Bimodal Ultrafine-Grained Al- dual phase microscale models to obtain the damage Mg Alloy,” Metallurgical and Materials Transactions pattern and damage growth versus number of load A, vol. 41, no. 4, pp. 795–801. cycles. For this purpose, several RVEs are extracted R. Huang, N. Sukumar, and J.-H. Prévost, (2003) “Mod- from the available optical microscopy (OM) images of eling quasi-static crack growth with the extended the real material. Then, XFEM is applied to the bimod- finite element method Part II: Numerical applica- al material and the brittle and ductile phases are dis- tions,” International Journal of Solids and Structures, tinguished using real values of parameters in fracture vol. 40, no. 26, pp. 7539–7552. criteria. In the next step, Paris equation coefficients are B. O. Han, E. J. Lavernia, Z. Lee, S. Nutt, and D. Witkin, obtained from the available da/dN-ΔK curves for dif- (2005) “Deformation behavior of bimodal nano- ferent phases and fatigue simulations are performed structured 5083 Al alloys,” Metallurgical and Mate- for different RVEs by means of XFEM code in ABAQUS. rials Transactions A, vol. 36, no. 4, pp. 957–965. Fatigue of automotive engine cylinder heads – A new model based on crack propagation and microstructure interaction Guillaume Morin, Romain Dejean, Jean-Michel Fiard, Mathieu Beranger Renault, Guyancourt, France Design of modern automotive internal combustion Diesel and gasoline engines, has made more and more engines has become an increasing challenging task in difficult to reach reliability targets. In parallel, develop- the past years due to increasing constraints in terms of ment costs reduction makes it necessary to raise sim- performance, fuel economy and emissions. Mechani- ulation model accuracy in order to get directly the op- cal and thermal loads increase on high specific power timized design with reduced physical validation tests. output engines, mainly turbocharged direct injection Cylinder head is a critical part in an internal combus- 169 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 tion engine. It has a great impact on performance via To overcome these difficulties, a new fatigue mod- intake and exhaust aerodynamic optimization and it el dedicated to cylinder heads in aluminum alloy has undergoes high mechanical and thermal loads direct- been developed in Renault powertrain engineering. ly linked to combustion process. Without efficient and The main characteristics are the followings. The model dedicated CAE tools, its development can quickly be- is based on a propagation approach in order to take come a blocking point. account typical characteristics of foundry alloy micro- The main reliability problem encountered during cyl- structure such as porosities which act as initial defects. inder head development is the appearance of fatigue Statistical distribution of these characteristics is includ- cracks during severe endurance tests. These cracks ed, which allows to explain and tackle experimental can in particular initiate in the coolant water jacket results scatter. Low cycle fatigue effect related to cyclic and lead to the complete part failure. Classically these thermal loads and high cycle fatigue effect related to cracks are associated mainly with combustion pressure combustion pressure are combined. The model is fitted alternate stresses and high cycle fatigue in infinite life thanks to an extensive crack propagation tests data- domain. To prevent their appearance, mechanical sim- base. Consistency with classical high cycle fatigue test ulation results are checked with a Haigh or Dang Van results is checked. criteria. But the comparison of predictions based on This paper will present the theoretical basis of this new these models with experimental results on engine re- model and the correlation with experimental results. veals several difficulties: crack initiation spots are not Benefit for cylinder head development based on real correctly located, scatter of crack sizes are not predict- examples will also be discussed. ed, and higher critical results on tests with thermal cy- clic loads are not taken into account. 170 Talks Topic D 1: In-situ microscopy and diffraction Talks Topic D 1: In-situ microscopy and diffraction 171 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 In-situ TEM deformation of lightweight alloys and local strain measurements with diffraction imaging Andrew M. Minor1,2 1Department of Materials Science & Engineering, University of California, Berkeley, USA 2National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, USA Besides the important results related to the effect of the evolution of strain during plastic deformation is of size on the strength of individual nanostructures, the great importance for correlating the defect structure ability to systematically measure the mechanical prop- with material properties. Here we demonstrate that erties of small volumes through nanoscale mechani- strain mapping can be carried out during in-situ defor- cal testing allows us to test samples that cannot eas- mation in a TEM with the precision of a few nanome- ily be processed in bulk form, such as a ion-irradiated ters without stopping the experiment. Our method of materials or single crystals of very specific alloys. This local strain mapping consists of recording large multi- talk will highlight recent advances with in situ Trans- dimensional data sets of nanodiffraction patterns using mission Electron Microscopy (TEM) nanomechanical a new high-speed direct electron detector. This dataset testing techniques that provide insight into small-scale can then be reconstructed to form a time-dependent plasticity and the evolution of defect structures in local strain-map with sufficient resolution to measure lightweight alloys such as Mg, Al and Ti. In addition to the transient strains occurring around individual mov- measuring the strength of small-volumes, measuring ing dislocations. CSL Σ3 and Σ9 activity as a deformation pathway in nano- crystalline Pd and AuPd Aaron Kobler1,2, Christian Kübel1, Horst Hahn1,2 1Karlsruhe Institute of Technology (KIT), Germany 2Technische Universität Darmstadt (TUD), Germany Most of our current understanding of the deforma- leads to user independent quantitative statistical infor- tion mechanisms active in nanocrystalline (nc) metals mation such as grain size. stems from in-situ deformation experiments on bulk This measurement and evaluation routine was applied materials using x-ray diffraction (XRD). However, XRD to magnetron sputtered PdxAu1-x thin film samples of cannot directly resolve the local deformation process- about 50 nm supported by an additional carbon film, es, e.g. grain growth or twinning. For a local analysis, which reduces strain localization during tensile tests. these processes are traditionally investigated using BF/ Grain growth and grain fragmentation as well as twin- DF-TEM. Though, varying contrast due to local orien- ning and detwinning have been observed to take place tation changes, bending and defects during in-situ BF- simultaneously at different locations. In addition, the TEM straining experiments make an accurate interpre- crystallite tracking revealed 40° and 60° orientation tation for nanometer sized grains difficult. On the other changes of individual crystallites indication a CSL rela- hand, the relatively new technique Automated Crystal tion of the crystallite before and after the deformation. Orientation Mapping (ACOM-TEM) allows for the iden- CSL-lattice flips are possible if multiple dislocations tification of crystallographic orientation of all crystal- are activated from different directions along the grain lites with crystal sizes <100 nm where EBSD reaches its boundaries, or generally, if pre-existing CSL boundaries limitation. are moved by dislocations. This investigation shows Recently, we combined ACOM imaging in STEM modus that dislocation mediated deformation mechanisms with in-situ straining inside a TEM [1], [2]. This combi- are still very active in nanocrystalline material, even nation was the key to new data evaluation based on though it was expected that grain boundary mediated orientation maps. By tracking individual crystallites processes would become more dominant. through a straining series the change of their orienta- tion can be evaluated in order to distinguish between Acknowledgement an overall crystallite rotation and sample bending. In This work was supported by the DFG under grant addition, twinning/detwinning and grain growth can FOR714. be directly followed and the automatic data evaluation 172 Talks Topic D 1: In-situ microscopy and diffraction References nanocrystalline metals,” Ultramicroscopy, vol. 128, [1] A. Kobler, A. Kashiwar, H. Hahn, and C. Kübel, pp. 68–81, Jan. 2013. “Combination of in situ straining and ACOM TEM: A [2] A. Kobler and C. Kübel, “In Situ Straining Analysis novel method for analysis of plastic deformation of with ACOM-TEM,” Imaging Microsc., no. 1, 2014. In-situ characterization of martensite plasticity by high reso- lution microstructure and strain mapping C. C. Tasan1, L. Morsdorf1, M-M. Wang1, D. Barbier2, O. Jeannin1, D. Raabe1 1Max-Planck-Institut für Eisenforschung GmbH, Duesseldorf, Germany 2Arcelor Mittal Research, Voie Romaine, Maizières-lès-Metz, France Mechanical behavior of martensite plays the most crit- in low-carbon martensitic steels [1]. ical role in many commercial steels used in strength re- Then, employing in-situ deformation experiments and quiring applications. Thus, there is an everlasting inter- high spatial resolution microstructure and strain map- est in identifying alloy design and thermo-mechanical ping, plasticity is investigated in different model mar- processing strategies to enhance martensite ductility tensitic microstructures. Results of the experiments and toughness. In this regard ferrous martensite, al- clearly demonstrate the heterogeneity of plasticity in though typically considered to fully lack plastic defor- all investigated materials. Coupling of the EBSD based mation capacity, can accommodate significant amount microstructure maps to the full-field strain measure- of micro- or even macro-plasticity prior to micro-crack- ments reveal that the local differences in crystallog- ing. However, a deeper understanding of the governing raphy, parent austenite grain size, defect density and factors in martensite plasticity is not yet fully available. boundary character play important roles in the result- To improve the fundamental understanding of the ing heterogeneity in martensite plasticity. Finally, we multi-scale characteristics of martensitic microstruc- also provide direct evidence on the key role of intro- tures and their micro-mechanical properties, first, a ducing thin films of austenite in enhancing martensite multi-probe methodology is developed and applied plasticity [2, 3]. to low-carbon lath martensitic model alloys. The ap- proach is based on the joint employment of electron References channeling contrast imaging (ECCI), electron backscat- Morsdorf, L., Tasan, C.C., Ponge, D., Raabe, D., 3D ter diffraction (EBSD), transmission electron microsco- structural and atomic-scale analysis of lath martens- py (TEM), atom probe tomography (APT) and nanoin- ite: effect of the transformation sequence, (submit- dentation, in conjunction with high precision and large ted, 2015) field-of-view 3D serial sectioning. This methodology Wang, M-M, Tasan, C.C., Ponge, D., Dippel, A-C., enabled us to resolve (i) size variations of martensite Raabe, D., Nano-laminate TRIP-TWIP steel with sub-units, (ii) associated dislocation sub-structures, (iii) dynamic strain partitioning and enhanced damage chemical heterogeneities, and (iv) the resulting local resistance, Acta Materialia, 85 (2015) 216-228. mechanical properties. The identified interrelated mi- Wang, M-M, Tasan, C.C., Ponge, D., Kostka, A., Raabe, crostructure heterogeneity is related to the martensitic D., Smaller is less stable: size effects on twinning vs. transformation sequence, which is proposed to intrin- transformation of reverted austenite in TRIP marag- sically lead to formation of a nano-composite structure ing steels, Acta Materialia, 79 (2014), 268-281. 173 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Complex analyses of mechanical and electrical performance of metallic thin films on flexible substrates combined with in-situ Reflectance Anisotropy Spectroscopy Andreas Wyss1, Matthias Schamel1, Richard Denk2, Michael Hohage2, Alla S. Sologubenko1, Ralph Spolenak1 1Laboratory for Nanometallurgy, Department of Materials, ETH Zurich, Switzerland 2Atomic Physics and Surface Science, Institute of Experimental Physics, Johannes Kepler Universität Linz, Austria For optimal electric performance, a flexible electronic films of different thicknesses: 50, 100, 200, 500 and device has to sustain large mechanical stresses without 1000 nm. losing its structural integrity. An effect of the mechan- Our study reveals that upon straining, the RA spectra of ical behavior of the whole system (substrate and thin both systems exhibit two main features. The first fea- metallic film) on electrical properties of the metallic ture grows linearly with strain and the second feature subsystem is very important and subject of extensive appears in later stages of straining. The saturation of studies. The thin film geometry exerts hard constraints the linear growth of the first feature indicates yielding or even excludes a number of conventional techniques and can therefore be used as yield point estimation. for mechanical testing. For the determination of yield These findings were proven by high resolution SEM mi- strength, synchrotron x-ray diffraction is commonly ap- crographs. The second feature and its evolution are as- plied. However, it is restricted by beam time availability sociated with irreversible deformation in the material and new characterization techniques are desired. as well as material properties for example absorption In our study we present complex in-situ characteriza- edges of segregated layers. Upon unloading, the first tion of electrical and mechanical behavior of fcc metal feature changes sign and gradually reduces, whereas thin films, Cu and Cu-Zn, on insulating polyimide sub- the second feature remains unchanged. The RA fea- strates. The change in the electrical resistance of the tures are shifted depending on the chemical compo- thin metallic films upon uniaxial tensile loading was sition as seen from Zn additions within the solubility monitored by a concurrent acquisition of reflectance limit of the Cu phase. anisotropy spectra. The latter technique is sensitive to Our results show that reflectance anisotropy spectros- changes in the strain state of the specimen, its phase copy is a suitable and reliable tool that allows dynamic and microstructural configurations. Since the mechan- monitoring of thin film strain states during deforma- ical behavior of thin metallic film is known to be thick- tion. Therefore, it can be employed to register micro- ness dependent, the experiments were performed on structural changes in the film upon straining. Crystallographic and mechanical charactization of micro-bic- rystal cantilevers S. Zaefferer1, N. Bozzolo2, S. Kleindiek3, A. J. Smith3 1 Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany 2 Ecole De Mines, Sofia-Antipolis 3 Kleindiek Nanotechnik, Reutlingen, Germany The influence on the mechanical behaviour of grain sequently, grain boundaries with interesting misorien- boundaries in crystalline materials depends on the tations or grain boundary plane are prepared, using crystallographic character of these boundaries. Grain focussed ion beam milling, to form a micro-cantilever boundaries are characterized by 5 rotational crystal- bicrystal. These bicrystals are mechanically tested by lographic parameters, including 3 for the misorienta- bending them inside of the SEM using a bending de- tion across the boundary and 2 for the grain boundary vice and micromanipulator developed by Kleindiek Na- normal. All 5 parameters influence properties like dis- notechnik. Finally, the deformed structure of the two location transmission strength or fracture propagation grains and the grain boundary is characterized using 2D resistance. or 3D EBSD. Geometrically necessary dislocation densi- We have developed a method, which allows character- ties and grain boundary damage are observed. ization, in a non-destructive manner, all 5 grain bound- The described approach is applied to polycrystalline ary parameters by a pseudo-3D-EBSD approach. Sub- 710 superalloys. 174 Talks Topic D 2: In-situ microscopy and diffraction Talks Topic D 2: In-situ microscopy and diffraction 175 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 In-situ micro-mechanical testing at the sychrotron Steven Van Petgem Neutrons and Xrays for Mechanics of Materials, Paul Scherrer Institut, Villigen, Switzerland A major challenge in metallurgy is to understand the in-situ Laue experiments during cyclic shear loading of relation between the microstructure of a metal and its Cu single crystals have been performed. Laue diffrac- behaviour under an applied load or temperature. This tion is very sensitive to crystal orientation and there- requires a detailed characterization of the evolution of fore allows tracking with high resolution the evolution the microstructure at different length scales through of the misorientation angles between the various dis- the determination of the crystal structure, defect den- location-poor regions that appear under cyclic defor- sity, grain size distribution, texture etc. mation. During last decade in-situ mechanical testing at the syn- (2) Transient testing is a well recognized technique to chrotron has become a widespread tool to investigate capture rate limiting deformation mechanisms. Most the evolution of the microstructure of single and poly- popular methods are strain rate jump and stress relax- crystals during deformation (Van Swygenhoven 2013). ation tests. Stress reduction tests are maybe less well Many such in-situ deformation tests are performed known, they have however shown to be a suitable tech- during continuous or interrupted uniaxial tensile and/ nique to determine the full transient response (Mekala or compression tests of bulk materials and thin films. 2011). In this work we report on stress reduction tests Several microstructural properties such as the devel- performed on electrodeposited nanocrystalline Ni. De- opment of intergranular elastic strains and texture pending on the magnitude of the stress reduction we evolution can be directly compared with results from, observe different regimes, revealling the presence of for instance, molecular dynamics simulations or crystal various deformation mechanisms. The results are in- plasticity modeling. While such tests have proven to terpreted in terms of a competition between plastici- be very useful, for further refinement of the existing ty based on dislocation nucleation/glide and recovery models it is crucial to obtain information from other, mechanisms at grain boundaries. more complex deformation tests. (3) Sintered nanoporous silver is currently considered In this work we highlight three such tests recently per- as a alternative bonding material in the electronic formed at the Swiss Light Source: (1) in-situ cyclic fa- packaging industry. For the development of lifetime tigue of Cu single crystals under shear conditions, (2) prediction models of components that include such stress reduction tests on nanocrystalline Ni and (3) the silver layers it is crucial to understand its thermome- deformation behaviour of porous silver films. chanical behaviour. In this work we focus on some key (1) It is well known that under cyclic fatigue of met- in-situ experiments that highlight the importance of als dislocation patterning occurs. The nature of the the porous microstructure on the overal mechanical resulting dislocation structure depends on several pa- behaviour. rameters, including stacking fault energy, dislocation mobility and loading conditions. To obtain a better Reference understanding of how these structures form a new Mekala, S. et al (2011) Philos. Mag. 91: 908-931 continuum dislocation-based constitutive model in the Van Swygenhoven, H.& Van Petegem, S. (2013) Mater. crystal plasticity finite element framework is currently Charact. 78: 47-59. under developement. In order validate this new model Optimizing Single Crystal Growth for Detector Applications using Energy-dispersive Neutron Imaging H. Matthias Reiche1, Sven C. Vogel1, Edith D. Bourret2, Adrian Losko3, Anton Tremsin3, Gregory A. Bizarri2, Martin M. Gascon2, Didier Perrodin2, Eric C. Samulon2 1Los Alamos National Laboratory, Los Alamos, U.S.A. 2Lawrence Berkeley National Laboratory, Berkeley, U.S.A. 3University of California Berkeley, Berkeley, U.S.A. Advances in neutron flux, neutron instrumentation, material synthesis and processing. Here, we present and sample environments over the past years allowed capabilities and results using recently developed en- the development of unique techniques to characterize ergy-dispersive neutron imaging and tomography ap- 176 Talks Topic D 2: In-situ microscopy and diffraction plied to optimizing single crystal growth. We show examples of the ex-situ characterization of Energy-dispersive neutron imaging and tomography single crystals grown with different processing parame- utilize isotope-specific neutron absorption resonanc- ters as well as our capability to study solidification and es to visualize the distribution of elements in the bulk crystallization processes in-situ with energy-dispersive (Tremsin 2013a & 2013b). Furthermore, so-called neutron imaging. Bragg-edges (Vogel 2000) allow measurements of lat- tice strains and thus imaging of e.g. the stresses in a References sample. Beam spots and penetration are both of the Reiche, H. M., Vogel, S. C., et al. (2012): A furnace with order of centimeters, allowing characterization of large rotating load frame for in situ high temperature single crystals grown e.g. for gamma particle detection. deformation and creep experiments in a neutron Homogeneous distribution of dopants, such as europi- diffraction beam line. Rev. Sci. Instr. 83 053901. um, is essential for the performance in the detector ap- Tremsin, A.S., Vogel, S.C., et al. (2013a): Non-destruc- plication while controlling and minimizing the stresses tive studies of fuel pellets by neutron resonance reduces mechanical failures. As with many other neu- absorption radiography and thermal neutron radi- tron techniques, sample environments (Reiche 2012) ography, J. Nucl. Materials 440 633–646. to e.g. study crystal growth by the Bridgman technique Tremsin, A.S., Vogel, S.C., et al. (2013b): Energy re- in-situ are possible. Such in-situ capabilities provide di- solved neutron radiography at LANSCE pulsed neu- rect feedback on how processing parameters such as tron facility, Neutron News 24 28-32. temperature, temperature gradient or growth speed Vogel, S.C. (2000): A Rietveld-approach for the analy- affect material properties such as the dopant distribu- sis of neutron time-of-flight transmission data, PhD tion, mosaicity, or stresses. thesis, Christian-Albrechts-University Kiel, Germany. Time-resolved (4D) in situ x-ray tomographic microscopy at TOMCAT: Understanding the dynamics of materials J.L.Fife1, F. Marone1, R. Mokso1, M. Stampanoni1,2 1Swiss Light Source, Paul Scherrer Institut, Villigen PSI, Switzerland 2Institute for Biomedical Engineering, Swiss Federal Institute of Technology and University of Zurich, Switzerland Non-destructive synchrotron-based x-ray tomographic of semi-solid grains in Al-Cu microstructures will be dis- microscopy is ideal for studying various materials sys- cussed. Such studies generate large amounts of data, tems in three and four dimensions (3D and 4D, respec- typically on the order of terabytes, that then require tively), and the TOMCAT beamline1 at the Swiss Light automated tools for visualizing and characterizing the Source is one of the premier beamlines in the world resulting phenomena. This talk will also underscore for such experiments. Spatial resolution ranges from these developments and summarize the future of me- 1-10µm with fields-of-view from 1-22mm, and tempo- chanical testing at TOMCAT. ral resolution is as fast as 0.1s for a full 3D data acqui- sition2. Contrast varies from standard absorption, typi- References cally used in metal and composite systems, to propaga- 1Stampanoni, M, Groso, A, Isenegger, A, et. al. (2006): tion- and grating-based phase contrast, predominantly Trends in synchrotron-based tomographic imaging: used for biological and other traditionally low-contrast the SLS experience.—Proceedings of the SPIE, 6318: materials. The efficient image processing pipeline pro- 63180M-1—63180M-14. vides a full 3D reconstruction within seconds3, making 2Mokso, R, Marone, F, Stampanoni, M, et. al. (2010): visualization close to real time. To exploit these state- Real time tomography at the Swiss Light Source.— of-the-art capabilities and to explore the dynamics of AIP Conference Proceedings, 1234: 87-90. materials at elevated temperatures, a dedicated la- 3Marone, F, Stampanoni, M. (2012): Regridding re- ser-based heating system has been developed4 and a construction algorithm for real-time tomographic mechanical testing device is being commissioned. imaging.—Journal of Synchrotron Radiation, 19: This talk will highlight the capabilities available at 1029-1037. TOMCAT as well as focus on recent achievements in 4Fife, JL, Rappaz, M, Pistone, M, et. al. (2012): Devel- dynamic, time-resolved experimentation. For exam- opment of a laser-based heating system for in situ ple, the behavior of geological materials at high tem- synchrotron-based x-ray tomographic microscopy.— peratures under simple dead-weight compression, 4D Journal of Synchrotron Radiation, 19: 352-358. self-healing of ceramics and 4D intergranular cracking 177 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Grain and subgrain high resolution diffraction from polycrys- talline bulk materials Ulrich Lienert1, Wolfgang Pantleon2, Gábor Ribárik3, Tamás Ungár3 1Deutsches Elektronen-Synchrotron, Photon Science, Hamburg, Germany 2Technical University of Denmark, Dept. of Mechanical Engineering, Lyngby, Denmark 3Eötvös University Budapest, Dept. of Materials Physics, Budapest, Hungary The penetration power of high energy X-rays enables top of a diffuse intensity distribution. These features the investigation of polycrystalline bulk materials by could be assigned to diffraction from almost disloca- diffraction techniques. In the conventional powder tion free subgrains and dislocation wall regions, re- diffraction mode, the observable intensities are aver- spectively. Based on the observation that the individu- ages over all grains that are oriented such that their al subgrains experience different elastic stresses, a re- selected reciprocal lattice vectors are sufficiently close finement of the classical composite model of the radial to the scattering vector. This mode is suitable for the peak broadening is proposed which resolves an overes- characterization of parameters describing grain en- timation of the dislocation density within the subgrains sembles such as the orientation distribution function. by the original model. Subgrain dynamics is followed in By polfigure inversion techniques average orientation situ during uninterrupted tensile deformation, forma- dependent properties can be recovered such as the tion of subgrains is observed concurrently with broad- strain distribution function, and average dislocation ening of Bragg reflections shortly after onset of plastic densities have been determined through fitting rou- deformation. When the traction is terminated, stress tines to radial line profiles. However, structural prop- relaxation occurs, but no changes in number, size and erties of individual grains such as the formation and orientation of the subgrains are observed. evolution of subgrains and their dislocation densities Grain-by-grain dislocation densities were obtained for are not accessible. tensile pre-deformed CoTi and CoZr intermetallics. A With the advent of 3rd generation high energy facilities, Monte-Carlo-type algorithm has been developed for high energy x-rays became available with unprecedent- the fitting of sets of radial peak profiles of individual ed brilliance and efficient area detectors have been de- grains. The technique discriminates dislocation den- veloped. Exploiting these advances, the three dimen- sities of different slip modes, slip systems, and dislo- sional X-ray diffraction (3DXRD) methodology has been cation character. The results confirm that the anoma- developed that enables the identification of diffraction lous ductility of the polycrystals as compared to single peaks from individual grains within polycrystalline bulk crystals is at least in part due to the existence of hard materials (Poulsen 2004). It has been demonstrated slip modes in the polycrystal which are only rarely ob- that the technique is sufficiently fast for in situ meas- served in deformation experiments of single crystals. urements during thermo-mechanical processing. We demonstrate that by extending the 3DXRD meth- References odology to high reciprocal space resolution intrinsic Poulsen, H.F. (2004): Three-Dimensional X-ray Diffrac- reciprocal space maps of reflections from individual tion Microscopy, Springer, Berlin. deformed grains can be recorded and interpreted in Pantleon, W., Wejdemann, C., Jakobsen, B., Poulsen, terms of (i) subgrain formation and evolution (Pantle- H.F., Lienert, U. (2014) – In: Strain and dislocation on et al. 2014), and (ii) dislocation characters and den- gradients from diffraction (Imperial College Press, sities (Ungár et al. 2014). The experimental configura- London), Barabash, R. & Ice, G. (eds.): 322-357. tions and selected case studies will be presented. Ungár, T., Ribárik, G., Zilahi, G., Mulay, R., Lienert, The formation of subgrains and their evolution was U., Balogh, L., Agnew, S. (2014): Slip systems and studied within copper samples during tensile defor- dislocation densities in individual grains of polycrys- mation. High resolution three-dimensional reciprocal talline aggregates of plastically deformed CoTi and space maps revealed a sub-structure of sharp peaks on CoZr alloys, – Acta Mater., 71: 264-282. 178 Talks Topic D 2: In-situ microscopy and diffraction Advanced Laboratory X-ray Microscopy : In Situ Materials Characterization and Diffraction Contrast Tomography Arno Merkle1, Christian Holzner1, Benjamin Hornberger1, Hrishikesh Bale1, William Harris1, Leah Lavery1 1Carl Zeiss X-ray Microscopy, Pleasanton, CA, USA This work presents new capabilities in X-ray Micros- trast, relying on spatially varying density within the copy (XRM) for 3D materials characterization. As a sample to create local variations in the attenuation of nondestructive technique, XRM presents some unique the incident x-ray beam. Reconstruction of the data opportunities for understanding material structure, yields a 3D map of sample density but cannot provide deformation, and performance. The non-destructive crystallographic information since even a polycrystal- nature of X-rays has made the technique widely ap- line structure of a single phase exhibits uniform densi- pealing, with potential for “4D” characterization, de- ty. In this work, a laboratory-based solution is present- livering 3D microstructural information on the same ed, termed diffraction contrast tomography (DCT). This sample as a function of time or imposed conditions. imaging modality is implemented on a laboratory X-ray The first section of this work will explore advance- microscope utilizing a polychromatic divergent beam. ments in XRM in situ material testing spanning a range The sample is incrementally rotated, creating a series of length scales from the micron to nanoscale. Incor- of diffraction patterns generated by the sample crystal- porating specialized in situ stages into the laboratory lites each time the Bragg condition is locally satisfied. X-ray microscopes enables control of material stimuli The patterns are then reconstructed to yield crystallo- such as temperature, flow, and mechanical load dur- graphic information including grain orientation, center ing simultaneous imaging. Several examples will be of mass, and size for a large number of grains. This is presented that illustrate the improved insight gained used to complement structural data obtained by tra- from observing the resultant volumetric changes, on ditional absorption-based tomography. This work will multiple length scales, and the fundamental links to present results on laboratory DCT along with discus- understanding how materials perform and deform in sion and comparison to alternative techniques. Merits their local mesoscale architecture. of the lab DCT method will be highlighted, particularly In the second section, new development of a 3D grain its non-destructive operation, leading again to poten- mapping technique will be discussed. Traditional X-ray tial 4D evolutionary studies by repeating the imaging tomography operates mainly based on absorption con- procedure numerous times on the same sample. 179 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic E 1: Size effects and small-scale mechan- ical behavior of materials 180 Talks Topic E 1: Size effects and small-scale mechanical behavior of materials Size dependent strength and its exploitation for length-scale engineered material systems Andy Bushby, David Dunstan Queen Mary University of London, London, UK Over the past 15 years experiments in micro-mechan- with the bulk or size independent term, t0. Further- ical testing have shown that smaller structures or more, how these parameters may change as a function smaller stressed volumes are stronger than the bulk of continued deformation also needs careful consid- properties of the same material (Artz 1998). These eration, since either hardening or softening can occur ‘size effects’ are often regarded as being due to differ- depending on the destination of dislocations that have ent phenomena, for instance depending on the crystal been generated. lattice type, bonding type and internal microstructure. The corollary of this approach is that a pure metal, They are observed in nanoindentation, mirco-pillar such as gold, may take any strength up the theoretical compression, micro-tension and torsion and thin foil limit depending on the size L, and that the minimum flexure, and as a function of microstructural features strength of a material can be predicted from only 2 such grains, sub-grains and twins (Kraft et al. 2010), im- parameters, L and t0. Understanding how to manipu- plying that length-scale itself is a strengthening mech- late these parameters opens the possibility to achiev- anism. ing strength through ‘length-scale engineering’. The For metallic materials that deform by dislocation mul- implications for exploiting size effects in engineering tiplication and flow, observable plastic deformation are clear, particularly using production methodologies depends on dislocation generation by the operation of such as multilayer deposition processes and repeat- sources. The minimum shear stress required depends ed roll bonding to create simple materials systems on the radius of curvature of dislocations in a given with ‘engineered’ microstructures to control strength space expressed by an equation of the form, through size alone. References A  ln L  Artz, E. (1998): Size effects in materials due to micro- t = t 0 +  + C  (1) structural and dimensional constraints: a compara-L  B  tive review, Acta Mater, 46, 5611 – 5626. where t0 is the bulk or size-indenpendent shear Kraft, O., Gruber, P., Monig, R. and D. Weygand, D. strength, the constants A, B & C are well-known ma- (2010): Plasticity in confined dimensions, Annu. terial or numerical constants. L is an effective length- Rev. Mater. Res., 40 293 - 317. scale which may be a combination of structure size, Dunstan, D.J. and Bushby, A.J. (2013): The scaling ex- grain size and deformation length-scale (plastic zone ponent in the size effect of small scale plastic defor- size). This shows that the underlying size dependence mation, Int. J. Plasticity 40 (2013) 152. has the form 1/L and adds to the bulk strength, t0, to Dunstan, D.J. and Bushby, A.J. (2014): Grain size de- give the size effects observed in different experiments. pendence of the strength of metals: The Hall-Petch effect does not scale as the inverse square root of Potentially, all the size dependent strength phenome- grain size, Int. J. Plasticity 53 (2014) 56 na associated with dislocation plasticity can be inter- D.J. Dunstan, B. Ehrler, R. Bossis, S. Joly, K.M.Y. preted using Equ 1, including structure size (Dunstan & P’ng and A.J. Bushby (2009): Elastic limit and Bushby 2013), grain size (Dunstan & Bushby 2014) and strain-hardening of thin wires in torsion, Phys. Rev. combinations of these (Dunstan et al. 2009). Letts, 103, 155501. The important considerations are which material length-scales should be associated with L and which 181 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Three-dimensional modeling of size effects in micromechani- cal testing Edgar Husser1, Erica Lilleodden1, Swantje Bargmann2 1Institute of Materials Research, Materials Mechanics, Helmholtz-Zentrum Geesthacht, Germany 2Institute of Continuum Mechanics and Material Mechanics, Hamburg University of Technology, Germany A finite-deformation strain gradient crystal plasticity a reasonable prediction of the deformation behaivor model is developed and implemented in a three-di- in the case of micro-pillar compression. Here, a typical mensional finite element framework in order to study distinct slip band formation is succesfully reproduced the influence of dislocation pile-ups in micro-mechani- by the presented theory. This is experimentally sup- cal testing of sinlge crystals, for instance in micro-com- ported by an EBSD analysis of the thinned cross-section pression experiments (Husser et al. 2014). The poten- of a deformed sample where the correlation between tial-based and thermodynamically consistent material the obtained lattice rotation and calculated GND distri- model is formulated in a non-local and non-linear ine- butions showed great accordance. lastic context in which dislocation densities are intro- duced via strain gradients. In the 3D context, the model References predicts both, the distribution of edge and screw type E. Husser, E. Lilleodden, S. Bargmann (2014): Compu- dislocations and accounts for, e.g., size effects due to tational modeling of intrinsically induced strain gra- accumulation of GNDs (geometrically necessary dis- dients during compression of c-axis-oriented magne- locations), dislocation interactions in terms of latent sium single crystal. In: Acta Materialia, 71, 206-219. hardening, and the Bauschinger effect. The robust S. Bargmann, B. Svendsen, M. Ekh (2011): An extend- solution algorithm is based on a numerically efficient ed crystal plasticity model for latent hardening in non-standard finite element strategy to solve the high- polycrystals. In: Computational Mechanics, 48, 631- ly coupled and highly nonlinear system of equations 645. and it is suitable for parallelization on two different B. Svendsen, S. Bargmann (2010): On the continuum ‘levels’. thermodynamic rate variational formulation of Presented numerical examples are directly related to models for extended crystal plasticity at large defor- experiments. For instance, it is shown that the inclu- mation. In: Journal of the Mechanics and Physics of sion of the strain gradient into the free energy enables Solids 58, 1253-1271. Dislocation grain boundary interaction in bi-crystalline micro pillars studied by in situ SEM and in situ µLaue diffraction Nataliya Malyar1, Christoph Kirchlechner1,2, Gerhard Dehm1 1Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany 2University of Leoben, Leoben, Austria Grain boundaries (GB) act as obstacles for dislocation nature at the micron-scale (Dehm 2009, Kraft, Gruber motion, promoting a higher strengths in polycrystalline et al. 2010) requires a thorough revisit of the published materials compared to the single crystalline counter theories on grain-boundary dislocation interaction. bodies (Hirth 1972). The grain size as a microstructur- In the present work bi-crystalline copper micro pillars al material length scale thereby inversely scales with were grown by the Bridgman method in various differ- the observed strength (Hall 1951, Petch 1953). This can ent orientations. Subsequently, micron sized compres- partly be attributed to the pile-up of dislocations on sion pillars which were single crystalline or possessed grain boundaries. a grain boundary were fabricated using FIB milling. Besides piling up at the grain boundary dislocations The mechanical tests were performed either in situ in can also transfer to the adjacent grain and thus lead the scanning electron microscope (SEM) or at a micro to slip transfer. This problem had been addressed dur- beam Laue (µLaue) diffraction beamline BM32 of the ing several studies in the past (Livingston and Chalmers ESRF synchrotron source. 1957, Hirth and Balluffi 1973, Bamford, Hardiman et al. Aim of the experiments was to understand the size de- 1986, Shen, Wagoner et al. 1988) but the advances in pendent dislocation-GB interaction. For this purpose understanding plasticity and it´s inherently stochastic four different grain boundaries had been investigated: 182 Talks Topic E 1: Size effects and small-scale mechanical behavior of materials (i) a general grain boundary not allowing for slip trans- Hall, E. O. (1951). “The deformation and ageing of fer in macroscopic models (ii) a general grain boundary mild steel: 3. Discussion of results.” Proceedings of with slip transfer (iii) a coherent S3 twin and (iv) a low the Physical Society of London Section B 64(381): angle grain boundary. 747-753. The mechanical tests show distinct differences be- Hirth, J. P. (1972). “Influence of grain-boundaries on tween the various grain boundary types: The different mechanical properties.” Metallurgical Transactions size dependent hardening rates, frequency of load 3(12): 3047-3067. drops, formation of slip steps and the possible grain Hirth, J. P. and R. W. Balluffi (1973). “On grain bounda- boundary motion will be discussed in the talk. ry dislocations and ledges.” Acta Metallurgica 21(7): Furthermore, our Laue data which is still not fully ana- 929-942. lyzed proofs for instance that dislocations are accom- Kraft, O., et al. (2010). Plasticity in confined dimen- modating at the macroscopically impenetrable grain sions. Annual Review of Materials Research. 40: boundary but no slip transfer happens. Based on these 293-317. findings models for hardening at the micron scale can Livingston, J. D. and B. Chalmers (1957). “Multiple slip be discussed and maybe revisited. in bicrystal deformation.” Acta Metallurgica 5(6): 322-327. References Petch, N. J. (1953). “The cleavage strength of polycrys- Bamford, T. A., et al. (1986). “Micromechanism of slip tals.” Journal of the Iron and Steel Institute 174(1): propagation through a high angle boundary in alpha 25-28. brass.” Scripta Metallurgica 20(2): 253-258. Shen, Z., et al. (1988). “Dislocation and grain-bounda- Dehm, G. (2009). “Miniaturized single-crystalline fcc ry interactions in metals.” Acta Metallurgica 36(12): metals deformed in tension: New insights in size-de- 3231-3242. pendent plasticity.” Progress in Materials Science 54(6): 664-688. Size effects and dislocation structure under torsion loading of single crystalline wires: a discrete dislocation dynamics study Daniel Weygand1, Peter Gumbsch 1,2 1Karlsruhe Institute of Technology, IAM, Germany 2Fraunhofer Institut für Werkstoffmechanik IWM, Freiburg, Germany The seminal experiments (Fleck et al. 1994) on the average plastic strain tensor is calculated locally on a deformation behaviour of metallic wires, where a so voxel discretization of the simulated volume. It is found called size effect in the mechanical response was ob- that the equivalent plastic strain determined in volume served, is still a matter of debate in the material science elements comprising the torsion axis is finite, not ex- community. Only little is know on the true dislocation pected from Flecks initial analysis. This observation can microstructure caused by torsion loading (Senger et al. be rationalized within a pile-up model, quite similar to 2011). the observations under bending (Motz et al. 2008). In the current contribution, the dislocation microstruc- This effect is most pronounced in small samples or for ture, density distribution and the local plastic strains low initial dislocation densities where forest hardening are analysed for different orientations of the torsion is negligible. It is also observed, that the equivalent axis within a discrete dislocation dynamics framework plastic strain depends on the voxel volume, used for (Weygand et al. 2002; Senger et al. 2011). Single crys- averaging. Furthermore the radially averaged disloca- talline Al beams with a square cross section are simu- tion density shows a decrease toward the surface, re- lated. First a simple system with one active slip system lated to dislocation escape. The thickness of this zone is studied, to evaluate the role of the slip plane incli- is quite similar for the different samples sized studied. nation with respect to the torsion axis on the plastic and hardening behaviour. A model is presented which References describes the initial yielding and hardening observed Fleck, N.A., G.M. Muller, M.F. Ashby, and J.W. Hutchin- in these simulations. Furthermore within this model son. 1994. “Strain Gradient Plasticity: Theory and setup, the role of cross-slip on the dislocation arrange- Experiment.” Acta Metallurgica et Materialia 42 (2): ment is illustrated. As a macroscopic measure, the 475–87. 183 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Motz, C., D. Weygand, J. Senger, and P. Gumbsch. Dynamics Simulation.” Modelling and Simulation in 2008. “Micro-Bending Tests: A Comparison between Materials Science and Engineering 19 (7): 74004. Three-Dimensional Discrete Dislocation Dynamics Weygand, D, L H Friedman, E Van der Giessen, and Simulations and Experiments.” Acta Materialia 56: A Needleman. 2002. “Aspects of Boundary-Value 1942–55. Problem Solutions with Three-Dimensional Disloca- Senger, J., D. Weygand, O. Kraft, and P. Gumbsch. tion Dynamics.” Modelling and Simulation in Materi- 2011. “Dislocation Microstructure Evolution in Cycli- als Science and Engineering. /10/4/306. cally Twisted Microsamples: A Discrete Dislocation Investigation of crystal plasticity of single crystal copper by using micro scale torsion test Kozo Koiwa1,2, Chuantong Chen1, Nobuyuki Shishido1,2, Masaki Omiya2,3, Shoji Kamiya1,2, Hisashi Sato1,2, Masahiro Nishida1,2, Takashi Suzuki4, Tomoji Nakamura4, Toshiaki Suzuki2,5, Takeshi Nokuo2,5 1Nagoya Institute of Technology, Nagoya, Japan 2Japan Scisnce and Technology Agency, Chiyoda, Tokyo, Japan 3Keio University, Yokohama, Japan 4Fujitsu Laboratories Ltd., Atsugi, Kanagawa, Japan 5JEOL Ltd., Akishima, Tokyo, Japan Recently, deformation of micro scale single crystal was copper was investigated by inverse analysis using the frequently investigated by using miniaturized speci- load-displacement curve which was obtained by simu- men. It is known that dislocation burst phenomenon lation and actual torsion test. occurred in case of conventional technique such as As a result, dislocation burst did not occur on load-dis- tensile and compression test because stress is homo- placement curve which was obtained by torsion test. geneous　 in specimen. Dislocation burst is the sud- However, in case that constitutive law which was den slip deformation of slip system through specimen, applied for macro scale specimen is used, load-dis- it makes deformation discontinuity around initial yield- placement curve which was obtained by torsion test ing area, and continuous deformation behavior around and simulation did not match even if any parameter dislocation burst cannot be obtained. However, in nano was used for crystal plasticity. Then, new constitu- scale structure such as LSI, since it is assumed that dis- tive law of micro scale crystal plasticity was devel- location burst does not occur because large deforma- oped. Flow stress shows gradual hardening behav- tion is restricted by other structural materials. Then, to ior after sudden drop behavior when resolved shear obtain continuous deformation characteristics of crys- stress of slip system reached initial flow stress. Similar tal plasticity around dislocation burst (initial yielding) drop behavior (stress-strain curve) was observed in area is important. New micro-scale torsion test meth- molecular dynamics simulation by G. Sainath. By us- od was developed. In this method, dislocation burst ing the new constitutive law, load-displacement curve around initial yielding region did not occur because of simulation matched that of torsion test, and crys- torsion stress field is inhomogeneous in specimen. In tal plasticity parameter was obtained as the result of this study, crystal plasticity of micro scale copper single fitting. It was demonstrated that the constitutive law crystal was investigated by using this torsion test and of micro scale crystal plasticity is different from that of finite element analysis. To incorporate crystal plasticity macro scale, and characteristic of the dislocation burst into the simulation, a program that reflects the crystal was obtained. plasticity constitutive relation of single crystals using the user subroutine UMAT of the finite element code References ABAQUS, which was developed by Huang. However, D. Kiener et al., A further step towards an under- macroscopic constitutive law of crystal plasticity which standing of size-dependent crystal plasticity: In situ was used for macro scale specimen may not be applied tension experiments of miniaturized single-crystal to micro scale specimen. Therefore, constitutive law of copper samples, Acta Materialia, Vol. 56, (2008), pp. micro scale specimen is discussed. 580-592 Torsion test specimen is fabricated by focused ion Y. Huang, Harvard University Report, MECH178 (1991). beam (FIB) using copper single crystal (99.9999% pu- G.Sainath et al., Molecular Dynamics Simulations of rity). The shape of specimen is half circular arc (with 3 Tensile Behaviour of Copper, International Congress µm radius, 1 µm width and thickness) of cantilever, and on Computational Mechanics and Simulation (IC- torsion test was conducted by indentation load at the CMS) IIT Hyderabad, (2012) end edge of cantilever. Crystal plasticity parameter of 184 Talk Topic E 2: Size effects and small-scale mechanical behavior of materials Talk Topic E 2: Size effects and small-scale mechan- ical behavior of materials 185 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Study of fatigue damage evolution in micron sized bending beams by in situ µLaue diffraction C. Kirchlechner1,2, P.J. Imrich3, J.-S. Micha4,5, O. Ulrich4,5, C. Motz6 1Max-Planck-Institute for Iron Research, Düsseldorf, Germany 2University of Leoben, Austria 3Erich Schmid Institute, Austrian Academy of Sciences, Leoben, Austria 4CEA-Grenoble/ Institut Nanosciences et Cryogénie, France 5CRG-IF BM32 at ESRF, France 6Saarland University, Saarbrücken, Germany Size dependent material properties of single crystalline Here we present the first in situ µLaue study investi- metals have been severely studied over the last dec- gating the low cycle fatigue of micro- bending beams: ade by performing micro-compression, -tension and 7µm sized single and bi-crystalline copper and silver –bending experiments. The experiments accompa- bending-cantilevers were FIB milled and analyzed with nied by complementary discrete dislocation dynamics a 500nm sized, polychromatic X-ray beam at BM32 (DDD) simulations remarkably showed the stochastic of the ESRF light source. The in situ loading showed nature of plastic flow at the micron scale. the formation and storage of geometrically necessary Besides monotone uniaxial deformation real devices dislocations, accompanied by the strong formation of Micro-Electro-Mechanical- Systems (MEMS) rou- of dislocation cell structures. During unloading and tinely have to withstand cyclic loading, which was also back-bending, the number of dislocations was dramat- shown to differ at small scales. The fatigue behavior of ically reduced reaching the initial dislocation densities. thin films has extensively been studied in the previous The stress-strain response of the samples showed cy- decade. Notable, dislocation patterns observed in bulk clic softening reaching a plateau after two cycles and materials are not necessarily observed at the micron a pronounced Bauschinger effect. This finding was ob- scale: If the grain size in pure Copper is reduced to less served for up to 100 cycles in single crystalline Cu and than 8µm persistent slip bands are rarely observed (Ka- Ag samples. In the talk, the influence of the different wazoe, Yoshida et al. 1999) but dislocation walls and stacking fault energy of Cu and Ag as well as the impact cell structures still exist (Zhang, Volkert et al. 2006). of a single grain boundary in Cu will be discussed. Dislocation patterns are replaced by individual disloca- tions as soon as film thicknesses of less than 1µm are References reached. Demir, E. and D. Raabe (2010). “Mechanical and mi- Recently the first micro fatigue experiments on FIB crostructural single-crystal Bauschinger effects: milled micro-cantilevers (Demir and Raabe 2010, Observation of reversible plasticity in copper during Kiener, Motz et al. 2010) were performed. The exper- bending.” Acta Materialia 58(18): 6055-6063. iments by Kiener and co-workers were accompanied Kawazoe, H., et al. (1999). “Dislocation microstruc- by DDD simulations showing a successive storage and tures in fine-grained Cu polycrystals fatigued at low escape of dislocations with high reversibility. Due to amplitude.” Scripta Materialia 40(5): 639-644. limited computational resources the study of steady Kiener, D., et al. (2010). “Cyclic response of copper sin- state dislocation patterns forming after several cycles gle crystal micro-beams.” Scripta Materialia 63(5): had not been possible by 3D-DDD so far. Also, in depth 500-503. analysis of the dislocation patterns in the deformed Zhang, G. P., et al. (2006). “Length-scale-controlled bending beams by TEM were not performed in the fatigue mechanisms in thin copper films.” Acta Ma- aforementioned experiments. terialia 54(11): 3127-3139. 186 Talk Topic E 2: Size effects and small-scale mechanical behavior of materials A comparative study of fatigue properties of nanoscale Cu films on a flexible substrate Bin Zhang1, Ying Zhang1, Xiao-Fei Zhu2, Xue-Mei Luo2, Guang-Ping Zhang2 1 Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shen- yang, P. R. China 2 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Scienc- es, Shenyang, P. R. China Fatigue at small scales is a key issue for the long-term of grain growth in the films were found. In addition, the reliability of micro/nano-devices. Recent investigations size of the grains containing twins in the as-deposited on fatigue behaviour of thin metal films have shown and annealed films, and that after fatigue loading a strong dependence of fatigue properties on length was also characterized. The variations in fatigue scales (Kraft et al., 2001; Schwaiger et al., 2003; strength and grain growth behavior with film thickness Schwaiger and Kraft, 2003; Wang et al., 2008). The are discussed. The results may provide a further physical origin for fatigue size effects was attributed to understanding of fatigue behavior of nanocrystalline the suppression of cyclic strain localization, leading to metal films. the gradual disappearance of typical bulk-like fatigue extrusions/intrusions(Zhang et al., 2006; Zhang et al., References 2010). Although these investigations provide a deep Kraft, O., Schwaiger, R., Wellner, P., 2001: Fatigue in insight into the fatigue mechanism of thin metal films thin films: lifetime and damage formation. Mater Sci with micron or submicron-scale grains, less work on Eng A319, 919-923. fatigue properties of nanocrystalline metal films has Luo, X.M., Zhu, X.F., Zhang, G.P., 2014: Nanotwin-as- been conducted(Zhang et al., 2008; Luo et al., 2014). sisted grain growth in nanocrystalline gold films In this study, nanocrystalline Cu films with different under cyclic loading. Nat Commun 5, 3021. thicknesses ranging from 25 nm to 250 nm were Schwaiger, R., Dehm, G., Kraft, O., 2003: Cyclic defor- deposited on a 125 µm-thick polyimide substrate mation of polycrystalline Cu films. Philos Mag 83, by a magnetron sputtering system. A comparative 693-710. investigation of fatigue properties of the Cu films Schwaiger, R., Kraft, O., 2003: Size effects in the fa- as-deposited and annealed were conducted under tigue behavior of thin Ag films. Acta Mater 51, 195- total strain control at room temperature. Variation in 206. microstructures of the fatigued samples and fatigue Wang, D., Volkert, C.A., Kraft, O., 2008: Effect of length damage behavior were characterized by transmission scale on fatigue life and damage formation in thin electron microscope (TEM) and high-resolution Cu films. Mater Sci Eng A493, 267-273. electron microscope. Zhang, B., Sun, K.H., Liu, Y., Zhang, G.P., 2010: On Experimental results show that the fatigue strength of the length scale of cyclic strain localization in fine- the nanocrystalline Cu films as-deposited and annealed grained copper films. Philos Mag Letts 90, 69-76. increases with decreasing the film thickness, which Zhang, G.P., Sun, K.H., Zhang, B., Gong, J., Sun, C., reveals a similar trend to that found in the Cu and Ag Wang, Z.G., 2008: Tensile and fatigue strength of films with grain size about micron or submicron-scales ultrathin copper films. Mater Sci Eng A483-84, 387- (Kraft et al., 2001; Schwaiger and Kraft, 2003; Wang et 390. al., 2008). Furthermore, TEM observations reveal that Zhang, G.P., Volkert, C.A., Schwaiger, R., Wellner, P., grain growth occurred in the as-deposited films after Arzt, E., Kraft, O., 2006: Length-scale-controlled fatigue. For comparison, the grain sizes in the annealed fatigue mechanisms in thin copper films. Acta Mater films and the annealed films subjected to fatigue 54, 3127-3139. loading were also examined. Evidently different extent 187 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Strain-dependent fatigue damage of nanocrystalline 930-nm-thick Au films Xue-mei Luo, Guang-ping Zhang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, PR China Quantitative studies have shown that fatigue behav- In addition, the fatigue damage behavior strongly de- iors in the thin metal films constrained by a substrate pended on the applied strain amplitude. Under the are different from that of their bulk counterparts 1.25% strain range, the films showed a bulk-like dam- (Schwaiger, et al. 2003, Schwaiger & Kraft 2003, Zhang, age behavior, i.e. the crack mainly initiated from the et al. 2006, Zhang & Wang 2008). Especially when the places with typical fatigue extrusions/intrusions in the film thickness or the grain size decreases below mi- coarsened grains with micron-scale grain size. Under crometer scale, it is hard for the typical micron-scale the 0.4% strain range, there were two main crack ini- dislocation structures to form in the film, like persis- tiation sites. One is the abnormally-grown grains along tent slip bands, etc. In addition, GBs in nanocrystalline the fully-developed cracks where the bulk-like fatigue metals usually become so unstable that grain growth extrusions/intrusions formed. Another is the grain always occurs at room and even low temperatures un- boundaries and quantitative intergranular cracks were der various loading modes (Cheng, et al. 2010, Fang, found. The mechanisms for grain growth and fatigue et al. 2011, Gianola, et al. 2008, Luo, et al. 2014, Pan, damage were discussed. It is concluded that diffe- et al. 2007, Soer, et al. 2004, Zhang, et al. 2005). How- ret grain growth behaviors and damge behaviors are ever, the fatigue behaviors of metal films with length found in the 930 nm thick nanocrystalline Au films un- scale ranging from micron to nanometer scales are not der cyclic loading. yet completely understood. In this study, we investigated grain growth and fatigue References damage behaviors of nanocrystalline Au films con- Cheng, S. et al. (2010): Phys. Rev. Lett. 104, 255501 strained by a polyimide substrate with the film thick- Fang, T. H. et al. (2011): Science 331, 1587 ness of 930 nm, in which fatigue damage happened Gianola, D. S. et al. (2008): Adv. Mater. 20, 303 within 2.6x104 cycles under a total strain range of Luo, X. M. et al. (2014): Nat. Commun. 5, 3021 1.25% and 1.8x106 cycles under a total strain range of Pan, D. et al. (2007): Nano Lett. 7, 2108 0.4%. Features of fatigue damage in the Au films main- Schwaiger, R. et al. (2003): Philos. Mag. 83, 693 ly exhibited multiple cracks. Under both strain ampli- Schwaiger, R. & Kraft, O. (2003): Acta Mater. 51, 195 tudes, abnormal grain and normal grain growth hap- Soer, W. A. et al. (2004): Acta Mater. 52, 5783 pened. There was similar extent of the normal grain Zhang, G. P. et al. (2006): Acta Mater. 54, 3127 growth under both strain amplitudes. Most abnormal Zhang, G. P. & Wang, Z. G. (2008): in Multiscale fatigue grain growth happened along the fully developed crack initiation and propagation of engineering ma- cracks due to the stress concentration in front of the terials: Structural integrity and microstructural wor- crack tip under 0.4% strain range. However, apart from thiness, edited by G. C. Sih (Springer Netherlands, the grain growth due to the crack propagation, much pp. 275. more grains could grow to micron scale before cracks Zhang, K. et al. (2005): Appl. Phys. Lett. 87, 061921 initiated inside the grains under 1.25% strain range. 188 Talk Topic E 2: Size effects and small-scale mechanical behavior of materials Influence of surface energy and dislocation pile-up on the size dependent strength of single-crystalline micro-pillars Bo Pan, Yoji Shibutani Dept. of Mechanical Eng., Osaka Univ., Japan Recent investigations show that the micro-mechanical inner responses of single-crystals (SC) present strong size de- σ = (αµb/ Lλ max +t 0 + 0.5µb r0 ) / SF , (3) pendent plastic yield strength by reducing dimensions where t is Peierls-Nabarro force, α is the geometric of micron- or nanopillars under uniaxial deformation 0parameter, SF is the Schmidt factor, also µ and b are (Uchic, 2004; Dimiduk, 2005; Greer, 2005). The simulat- the shear modulus, and the Burgers vector, respective- ing and theoretical researches show their explanations ly. In this case, the stress of the filed can be finally ob- from the boundary, source truncation and dislocation tained as starvation, respectively (Fan, 2012). But few researches focus on describing the dislocation pile-up effect and the surface energy effect on the boundary in SC on size σ ( αµb= +t 0 + 0.5µb ) / SF gΟ0 (1-ν )r + . (4)0 effect. Lλ max A In this work, the understanding of the size effect dom- It is shown that the “Hall-Petch relation” holds even in inantly derives from the dimensional grain size and SC. The process of simulations indicated that the star- physical interface, besides the inner defect micro- vation of dislocation sources is one reason for the ob- structures. At present, discrete dislocation simulation served size effect. Furthermore, it can be found that results show that the boundary condition affects the the surface effect from the geometries and the inner strength by wall thickness (Fan, 2012). The wall thick- strength from the inner microstructures interplay each ness has the physical nature of surface effect, and the σ surface other, and both influence on the yielding strength, surface energy can affect on the surface stress . which has the size-dependent characteristic. Thus, the plastic strength can be written as σ = σ +σ surface = σ inner0 +σ surface , (1) References σ Uchic, M.D. Dimiduk, D.M. Florando, J. Nix, W.D. where 0 is the conventional plastic strength which is (2004): Sample Dimensions Influence Strength and not affected by surface geometrics, and it can also be represented as σ inner Crystal Plasticity. Science, 305: 986-989.. Based on the principle of mini- surface Dimiduk, D.M. Uchic,M.D. Parthasarathy T.A. (2005): mum potential energy, the surface stress σ can be Size-affected single-slip behavior of pure nickel mi- derived as crocrystals. Acta Mater. 53: 4065–4077. σ surface =gΟ0 (1-ν ) / A , (2) Greer J.R., Oliver W.C., Nix W.D. (2005): Size depend- where is the surface energy density, Ο , A are the ence of mechanical properties of gold at the micron g 0 perimeter and area of the initial cross section and ν is scale in the absence of strain gradients. Acta Mater. the Poisson’s ratio. According to the dislocation pile-up 53: 1821–1830. configuration, the inner strength σ inner can be obtained Fan, H. Li, Z. Huang, M. (2012): Size effect on the com- by considering the effect of microstructures, such as pressive strength of hollow micropillars governed by effective length of dislocation source λ max , dislocation wall thickness. Scripta Materialia. 67: 225–228. pile-up length L , dislocation density r0 , the number of dislocation sources and so on. It can be expressed as 189 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 In situ fracture tests of brittle materials at the microscale Giorgio Sernicola, Tommaso Giovannini, Rui Hao, T. Ben Britton, Finn Giuliani Imperial College London, Department of Materials, London, United Kingdom Understanding fracture behaviour especially at the focused ion beam (FIB) milling and loading them in-situ grain boundaries is of vital importance to extend the in an SEM using a nanoindenter with a wedge-shaped life of structural ceramics. Currently the processing tip. This has two benefits: the sample is well aligned parameters of many commercial composite ceramic for a controlled test; images are recorded during the products are largely empirically derived and there- test for later anlysis. fore result in a large number of different microstruc- This testing approach produces data that can be ana- tures and properties. Development of new materials lysed to directly measure the geometrical parameters and controlled processing routes will greatly benefit required to solve the equation. from knowledge of the fracture energy of phase and Our tests have proved it is possible to initiate and sta- interface present. This requires development of new bly grow a crack in a controlled manner in ceramic fracture testing methods capable of granting high spa- materials and our fracture energy results have been tial resolution and high control over the area to test. validated against prior macro-scale fracture data. This Further benefits of these ‘small scale’ approaches will approach is being extended to multi-phase materials enable testing of specimens for which big volumes are with unknown materials properties and extends our not available (e.g. thin films, coating, or simply samples arsenal of small-scale characterisation techniques re- of dimensions limited by production process). quired to generate new processing strategies for the Historically indentation has been largely employed to next generation of materials design. determine the fracture toughness of brittle materials. However, its spatial resolution is limited by the crack- References ing threshold (Pharr 1998), namely the load at which Anstis, G. R., P. Chantikul, B. R. Lawn and D. B. Mar- a crack is initiated, being the size of the impression shall (1981). “A Critical Evaluation of Indentation proportional to the load applied. Moreover, several Techniques for Measuring Fracture Toughness: I, studies (Anstis, Chantikul et al. 1981, Quinn and Bradt Direct Crack Measurements.” Journal of the Ameri- 2007) discourage the use of indentation induced cracks can Ceramic Society 64(9): 533-538. to measure fracture toughness. Armstrong, D. E. J., A. J. Wilkinson and S. G. Roberts Recently, several techniques have been developed (2011). “Micro-mechanical measurements of frac- using small scaled mechanical testing, based within a ture toughness of bismuth embrittled copper grain nanoindenter, changing tip and sample geometries, boundaries.” Philosophical Magazine Letters 91(6): including: micropillar compression (Östlund, Howie et 394-400. al. 2011); microcantilever bending (Di Maio and Rob- Di Maio, D. and S. G. Roberts (2005). “Measuring erts 2005, Armstrong, Wilkinson et al. 2011); and dou- fracture toughness of coatings using focused-ion- ble-cantilever compression (Liu, Wheeler et al. 2013). beam-machined microbeams.” Journal of Materials However, the majority of the published works utilises Research 20(02): 299-302. complex geometries resulting into complex analysis of Lawn, B. R. (1993). Fracture of brittle solids. Cam- force distribution and stress intensity factor. bridge, Cambridge University Press. Our approach builds upon the work of Lawn (Lawn Liu, S., J. M. Wheeler, P. R. Howie, X. T. Zeng, J. Michler 1993), who showed that a practical test geometry to and W. J. Clegg (2013). “Measuring the fracture calculate the fracture energy G is that of a double-can- resistance of hard coatings.” Applied Physics Letters tilever beam under constant wedging displacement. 102(17): 171907. We use this geometry at the small scale to directly Östlund, F., P. R. Howie, R. Ghisleni, S. Korte, K. Leifer, measure fracture energy in brittle materials and small W. J. Clegg and J. Michler (2011). “Ductile–brittle volumes. transition in micropillar compression of GaAs at Using Lawn’s analysis, G is given by: room temperature.” Philosophical Magazine 91(7- 9): 1190-1199. G = 3Eh2d3/4c4 Pharr, G. M. (1998). “Measurement of mechanical where E is the elastic modulus, c the crack length and properties by ultra-low load indentation.” Materials d and h the half-width of the beam and the wedging Science and Engineering: A 253(1–2): 151-159. displacement respectively. Quinn, G. D. and R. C. Bradt (2007). “On the Vickers We replicate this configuration in our tests fabricating Indentation Fracture Toughness Test.” Journal of the double-cantilever beams of micrometric dimensions by American Ceramic Society 90(3): 673-680. 190 Talks Topic E 3: Size effects and small-scale mechanical behavior of materials Talks Topic E 3: Size effects and small-scale mechan- ical behavior of materials 191 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Smaller is not always stronger – inverse scale effect on met- al- ceramics interface strength observed in LSI interconnect structures Shoji Kamiya1,2, Nobuyuki Shishido1,2, Kozo Koiwa1,2, Masaki Omiya2,3, Hisashi Sato1,2, Masahiro Nishida1,2, Takashi Suzuki4, Tomoji Nakamura4, Toshiaki Suzuki2,5, Takeshi Nokuo2,5 1Nagoya Institute of Technology, Nagoya, Japan 2Japan Scisnce and Technology Agency, Chiyoda, Tokyo, Japan 3Keio University, Yokohama, Japan 4Fujitsu Laboratories Ltd., Atsugi, Kanagawa, Japan 5JEOL Ltd., Akishima, Tokyo, Japan Smaller is stronger. It is so frequently mentioned since crack extension suggested the reasons, where larger the beginning of nano-technology era, and even today structure needs longer distance of crack extension to (Kunz et al. 2011, Kraft et al. 2010), in the context that completely debond larger area of the interface leading smaller volume of materials has less defects leading to to larger volume of plastic deformation with severer higher apparent strength. However, it may not always strain level at the crack tip. Smaller was not stronger true, especially for the complicated mechanical struc- in such a case. tures in microscale devices, as explained in the follow- Smaller specimens had not only smaller average ing. strength. Relative standard deviation (standard devia- Large scale integrated circuits (LSI) typically have tion devided by average) of the strength distribution sub-micron mechanical structures, which are intercon- also increased sharply with smaller ones, which was nect wiring systems fabricated on top of silicon chips due to different crystal orientations of grains and grain for current supply and signal readout. They consist of a boundaries underneath the specimens. In contrast to layer of insulator with trenches filled with electroplat- macro-scale structures where such intrinsic structures ed copper as narrow metal wires and another capping of materials are smeared out to yield a homogenized insulation layer on top to seal the wires. A number of properties, characteristics of individual grains and their these layers are usually stacked alternately to compose combinations far more directly influence the strength. multi-layered 3D interconnect structures. Therefore Therefore extremely weak ones also come out far LSI has many weak interfaces, which occasionally caus- more likely. es serious reliability issues even today (Kengeri 2014). These trends newly found as explained above could be Although the strength properties of such interfaces a kind of nano-tech syndrome, possibly being a com- are well surveyed, commonly with four-point bending mon risk to the reliability of small scale structures. interface fracture test performed with lab-scale test- More detailed pathology of such a syndrome and pos- ing machines (Charalambides et al. 1989) and the in- sible diagnosis to evaluate the risk for the reliability terconnect structures are designed accordingly, crack of LSI interconnect structures will be discussed in the propagation to destroy them occasionally takes place presentation. especially when LSI chips are packaged and mounted on board causing the extra stress application. Is the References strength of four-point bending specimens different Kunz, A. et al. (2011): Size effects in Al nanopillers: from that of the actual sub-micron scale interfaces ? Single crystalline vs. bicrystalline – Acta Mater., We dare measured the strength in life size. Insulation 59:4416-4424. layer on top of copper line was machined by focused Kraft, O. et al. (2010): Plasticity in confined dimen- ion beam (FIB) into specimens of square brick-like sions – Annu. Rev. Mater. Res. 40:293-317. shape. They were prepared in different scales rang- Kengeri, S. (2014): The critical need for innovations in ing from 10 μm down to 200 nm. Interface strength advanced packaging to drive semiconductor growth was evaluated in terms of energy release rate (J/m2) in the FinFET era – http://www. semiconsingapore. by pushing their sidewalls with a diamond stylus to org/node/2466. extend interface cracks. As the result, the average Charalambides, P.G. et al. (1989): A test specimen for strength levels drastically decreased from 11 J/m2 to determining the fracture resistance of bimaterial 2 J/m2 with the size of specimens decreasing from 10 interfaces – J. Appl. Mech. 56: 77-82. μm to 200 nm. Finite element simulation of interface 192 Talks Topic E 3: Size effects and small-scale mechanical behavior of materials Characterisation and Mechanical Properties of the Boundary Layers of Soft Magnetic Composites Tabea Schwark, Ruth Schwaiger, Oliver Kraft Karlsruhe Institute of Technology, Germany are then further processed by a powder metallurgical into the boundaries and the interior of the particles route. The insulating coating reduces losses related to do not show a significant difference regarding Young’s eddy currents. In comparison to traditional laminated Modulus and hardness. Also, crack formation in the steels, the SMC offers several advantages. For instance, boundaries was not detected. These results indicate the combination of their isotropic nature and new that on a short length scale the layers provide good ad- shaping possibilities opens up the possibility to design hesion between the particles. In order to elucidate this new 3D components. Those new designs, however, aspect further, beam bending experiments are current- may demand besides the magnetic properties of the ly underway. Using focused ion beam preparation, mi- SMC more and more a certain mechanical robustness cro-scale beams containing boundaries are produced of the material. for characterizing their fracture behaviour. The mechanical properties of the SMC are determined In summary, it was possible to identify in the SMC dif- by the combination of the soft matrix and the brittle ferent types of boundaries with transmission electron boundaries between the particles. First characterisa- microscropy. On a short scale, the boundaries do not tion of the boundaries of SMC was reported in [1] and show the expected very brittle behaviour as illustrated [2]. However, this was a former generation of SMC with by the nanoindentation tests. This finding indicates that a simpler boundary structure. The SMC investigated in the lacking robustness of the material might be rather this work contains additional iron oxide layers at the related to large defects remaining in the material af- particle boundaries changing their characteristics with ter preparation than to intrinsically brittle boundaries. respect to the mechanical properties. The latter type of SMC was studied in terms of the transverse rupture References strength as a function of particle size and pressure as [1] Shin Tajima, T. H., Mikio Kondoh, Masaki Sugiyama, well as in terms of the magnetic properties [3]. Kiyoshi Higashiyama, Hidefumi Kishimoto and Ta- In this presentation, we are addressing the micro-me- dayoshi Kikko (2004). “Properties of High Density chanical behaviour of the boundaries and the resulting Magnetic Composite (HDMC) by Warm Compaction relationship to the overall mechanical and magnetic Using Die Wall Lubrication” Materials Transactions properties. 45(6): 1891-1894. The SMC consists of pure iron particles coated by a thin [2] Oikonomou, C., E. Hryha, et al. (2012). “Develop- inorganic, phosphorous layer and iron oxide layers at ment of methodology for surface analysis of soft the boundaries. Processing includes after compaction magnetic composite powders.” Surface and Inter- an annealing during which the strength-enhancing ox- face Analysis 44(8): 1166-1170. ide layers are formed. Transmission electron microsco- [3] H. G. Nguyen, G. D., A. Hartmaier (2013). Grenze py was used to determine the structure of the bounda- der Einsetzbarkeit eines weich-magnetischen Pul- ries. Three types of boundaries were identified: bound- ververbundwerkstoffes aus Sicht der Mechanik. 19. aries that grow within pores, boundaries which had Symposium Verbund-werkstoffe und Werkstoffver- several 100 nm space to grow and boundaries which bunde. Karlsruhe. had significantly less space to grow. Nanoindentation Multiscale Modelling of Damage and Failure in a Biological Hierarchical Material Ingo Scheider1, Songyun Ma2, Ezgi Yilmaz3, Swantje Bargmann1,2 1Institute of Materials Research, Materials Mechanics/ACE-Centre, Helmholtz-Zentrum Geesthacht, Germany 2Institute of Continuum and Material Mechanics, Hamburg University of Technology (TUHH), Germany 3Institute of Advances Ceramics, Hamburg University of Technology (TUHH), Germany Dental enamel is a heterogeneous anisotropic materi- explore the structure-property relationship of dental al, showing an optimal reliability with respect to the enamel and discover how the material achieves its various loads occurring over years. This study aims to structural functions through hierarchical design, ex- 193 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 tending the study presented in Bargmann et al., (2013). microstructural parameters that cannot be measured To this end, the microstructure of enamel at two hierar- experimentally; for example: The interface damage chical levels, namely parallel rods consisting of bundles properties between the nano-sized mineral fibres and of mineral fibres, was modelled and mechanical prop- the thin protein matrix can be estimated by enforcing erties were evaluated in terms of strength and tough- the interface toughness to be low enough such that ness with the help of a multiscale modelling method. debonding occurs but as high as possible to achieve The technique used here consists of two steps for each the highest possible strength. hierarchy level; that is (a) the simulation of a repre- Another case which illustrates the usefulness of mi- sentative unit cell including the material models for crostructural modelling: In order to state a reason for the participating microstructural elements and (b) the the damage-tolerance behaviour of enamel in relation homogenization with respect to deformation and fail- with the nano-sized crystallites and multiple hierar- ure in order to retrieve the material model for the next chies, the size of crystallites below which the structure hierarchy level. For part (a) the representative unit cell becomes insensitive to flaws were studied by the rep- contains appropriate hyperelastic material models for resentative unit cell. The results reveal that the flaw the constituents and also damage models for several tolerance size of enamel is about 50 nm, the same size types of damage. Three kinds of damage are included: as the mineral fibres appear in dental enamel. Breaking of the fibres, debonding of the fibres from the matrix and matrix damage. All damage models are re- References alized by cohesive interface elements with respective S. Bargmann, I. Scheider, T. Xiao, E. Yilmaz, G. Schnei- model parameters. The interface elements are placed der, N. Huber (2013) Towards bio-inspired enginee- such that various crack paths and failure mechanisms ring materials: Modeling and simulation of the may occur. The parameters identified during the ho- mechanical behavior of hierarchical bovine dental mogenization phase (b) are strongly dependent on the structure. Computational Material Science, 79, 390- geometry of the microstructure and thus the failure 401. mechanism. I. Scheider, T. Xiao, E. Yilmaz, G. Schneider, N. Huber, S. The established models were validated by comparing Bargmann (2014) Damage modeling of small scale with the measured stress-strain curves on two hierar- experiments on dental enamel with hierarchical chical levels, see Scheider et al. (2014). The results lead microstructure. Acta Biomaterialia, accepted manu- to a close agreement between experiment and simu- script lation, which gives further evidence for some of the Surface properties of biopolymer films - Morphology, adhe- sion and friction Maurice Brogly, Ahmad Fahs, Sophie Bistac Université de Haute Alsace, LPIM, Mulhouse, France For pharmaceutical applications, cellulose derivatives at nanoscopic and macroscopic scales. Our expertise in are promising raw materials for coatings or films ob- contact mode Atomic Force Microscopy (AFM) allows tained from aqueous systems. A case study is present- us to quantify the mechanical behaviors at nanoscale. ed on hydrophilic biopolymer for the preparation of The influence of additives on HPMC structuration and oral controlled drug delivery systems. Additives such morphology, permeation, hydrophilic/hydrophobic as plasticizers, surfactants, lipids, colorants or other character as well as surface mechanical characteritics film-forming polymers are frequently incorporated such as adhesion and friction are evaluated. The re- into biopolymer matrices to pwroduce high quality sults clearly underline the strong dependence of film drug protective films. The matrix used is Hydroxypropyl properties on additive nature, concentration or water methylcellulose (HPMC). Additives such as stearic acid sensitivity and the interplay with additive-biopolymer and polyethylene glycol (PEG) are added to improve matrix compatibility. some specific film surface properties such as adhesion Stearic acid additive has a strong influence on HPMC and friction. The study investigates then the influence surface properties and morphology. The surface struc- of such hydrophilic plasticizer (polyol) and hydrophobic ture of HPMC films shows the presence of granular na- excipient (fatty acid) on the surface properties of free no-domains, which disappear with fatty acid content. HPMC films. A sharp variation of nano-adhesion and nano-friction The aim of this work is to formulate HPMC films by in- forces is observed with addition of fatty acid. The re- troducing additives, to explore their surface properties sults show that the addition of only 1% (w/w HPMC) and to investigate the adhesive and frictional properties of stearic acid induces a strong decrease (25%) of the 194 Talks Topic E 3: Size effects and small-scale mechanical behavior of materials surface free energy. The hydrophobic character be- The present study underlines the strong dependence comes predominant and the non-dispersive compo- of surface film properties on additive concentration nent to the surface energy tends towards zero. Tapping and/or water sensitivity. Formulation appears then as mode topographic images show that the surface mean an original and simple way to tune surface morpholo- roughness of the formulated films decreases with the gy and surface properties of bio-based polymer films. introduction of stearic acid. These results suggest that Finally the present study also shows that AFM is a stearic acid molecules can migrate at the film surface. powerful tool for studying surface adhesion and slid- As a consequence the torsional forces measured on ing properties of cellulose based formulated films for the basis of AFM nano-friction experiments decrease. pharmaceutical applications such as coatings and films. Nano adhesion results confirm this tendency and sug- gest the presence of a weak boundary layer at the film References surface, the formation of which is driven by a phase Brogly, M., Awada, H., Noel O. (2009), in Nanosciences separation process. and Technology, Applied Scanning Probe Methods PEG additives induce an increase of the surface hy- XI, B.Bhushan & H. Fuchs Eds., Springer, 73-93; Ber- drophilicity and affect HPMC morphology by insertion lin Heidelberg. mechanisms. Swelling of HPMC clusters is observed as Fahs A., Brogly M., Bistac S., Schmitt M. (2010), Carbo- PEG content increases hydrate Polymers, 1: 105; PEG additives also induce an increase of the surface Brogly M., Fahs A., Bistac S. (2011), In Nanaoscience free energy. At the nano scale, the increase of PEG and Technology, Scanning Probe Microscopy in content causes an increase of friction and adhesion Nanoscience and Nanotechnology, B.Bhushan Ed., forces. Good correlation is obtained at macro scale. Ex- Springer, 473-504; Berlin Heidelberg. perimental results underline the major role of capillary forces at the nano scale and evidence that PEG behave as a lubricant at macro scale. Microstructure evolution of Cu/Au and Cu/Cr multilayers un- der cyclic sliding Zhao-Ping Luo1, Guang-Ping Zhang2, Ruth Schwaiger1 1Karlsruhe Institute of Technology, Institute for Applied Materials, Germany 2Institute of Metal Research, Chinese Academy of Sciences, Shenyang, P. R. China Nanoscale metallic multilayers exhibit high strength, (TEM) and scanning TEM with high-angle annular dark- good fatigue properties and wear resistance, high ther- field (HAADF-STEM) imaging on cross-sections pre- mal stability, as well as excellent irradiation tolerance pared by focused ion beam (FIB). (Clemens et al. 1999; Beyerlein et al. 2014). Previous For the Cu/Au multilayers, grain growth and a reduction investigations have illustrated that the strength and of the individual layer thickness were observed in both plastic deformation are length scale dependent but the Cu and Au layers at the early stage of deformation also strongly controlled by the interface structure, (1-50 cycles). For sliding cycle numbers between 50 and which determines the interface barrier strength and 100, the deformed layers started to curve and formed a slip transmission (Li & Zhang 2010; Wang & Misra vortex structure. In the next stage of deformation (500- 2011). However, a more detailed description of defor- 1000 cycles), nanostructures were formed in the sliding mation behaviors and the predominant mechanisms track. For the Cu/Cr multilayers, plastic deformation are still needed for our understanding of these supe- and microstructural changes were mainly concentrat- rior properties. ed on the Cu layers at the early stage of deformation. In this study, two types of nanoscale multilayers, Cu/ Then, fracture of the Cr layers whereas the vortex for- Au (which is a miscible semi-coherent fcc/fcc struc- mation did not occur. In the range between 500 and ture) and Cu/Cr (which is an immiscible incoherent 1000 cylces, a mixed nanostructure was formed in the fcc/bcc structure), were studied. Cyclic sliding experi- worn zone. The differences in the deformation micro- ments which induce large strains in the samples were structrues betwenn Cu/Au and Cu/Cr multilayers indi- conducted using a nanoindenter. The microstructures cate that different deformation mechanisms are active. underneath the sliding tracks subjected to 1-1000 cy- The deformation behavior of the two different material cles of sliding were investigated by scanning electron systems will be discussed with respect to the interface microscopy (SEM), transmission electron microscopy effect and resulting microstructural changes. 195 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 References Li, Y. P. & Zhang, G. P. (2010): On plasticity and fracture Beyerlein, I. J., Mayeur, J. R., Zheng, S., Mara, N. A., of nanostructured Cu/X (X=Au, Cr) multilayers: The Wang, J. & Misra, A. (2014): Emergence of stable in- effects of length scale and interface/boundary. Acta terfaces under extreme plastic deformation. PNAS; Materialia; 58: 3877-3887. 111: 4386-4390. Wang, J. & Misra, A. (2011): An overview of inter- Clemens, B. M., Kung, H. & Barnett, S. A. (1999): face-dominated deformation mechanisms in metal- Structure and strength of multilayers. MRS Bulletin; lic multilayers. Current Opinion in Solid State and 24: 20-26. Materials Science; 15: 20-28. Toward the modulation of interface barrier strength of Cu/ Au nanolayered composites Xi Li1, Guang-Ping Zhang1, 1 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Scienc- es, Shenyang, P. R. China 2 Karlsruhe Institute of Technology, Institute for Applied Materials, Germany The Interface barrier strength (IBS), which describes microstructures indicates that the change in grain sizes the resistance for dislocations to cross an interface, and the amount of twinning in both Cu and Au layers is a key factor that controls the ultrahigh strength of induced by annealing did not significantly affect the metallic nanolayered composites (Koehler, 1970; Hoag- H-P slope of the material. The HRTEM characterization land et al. 2002; Li, et al. 2007; Yan, et al. 2013). Several reveals that element interdiffusion between the Cu theory models have been proposed to describe the layer and the adjacent Au layer leads to a compositional strengthening mechanisms in multilayered composites gradient at the interface. A detailed analysis for effects and primary contributions to IBS, such as modulus of the compositional gradient on the resistance to modulation and lattice parameter mismatches et al. dislocation crossing the interface was conducted. (Koehler, 1970; Hoagland et al. 2002; Li, et al. 2007; Thus, it is concluded that the interface structure of the Yan, et al. 2013). However, the variation of interface Cu/Au nanolayered composites has become the most microstructure induced by element interdiffusion important factor in governing the IBS. These results and its influence on the IBS in metallic nanolayered provide important guidelines for the interface design composites are still not clearly understood (Chu and of high performance nanolayered composites. Barnett, 1995). In this study, Cu/Au nanolayered composites with References individual layer thickness ranging from 25 nm to Koehler, J.S., 1970: Attempt to Design a Strong Solid. 250 nm were prepared by DC magnetron sputtering Phys Rev B 2, 547. (Zhang, et al. 2006). The Cu/Au nanolayered Hoagland, R.G., Mitchell, T.E., Hirth, J.P., Kung, H., composites were annealed at 100, 200 and 300 °C 2002: On the strengthening effects of interfaces in for 30 minutes, respectively. Mechanical properties multilayer fcc metallic composites. Philos Mag 82, of the nanolayered composites were investigated 643 - 664. using a nanoindenter. The microstructures of the Li, Y., Zhang, G.P., Wang, W., Tan, J., Zhu, S., 2007: On nanolayered composites were characterized by interface strengthening ability in metallic multilay- transmission electron microscopy (TEM) and high-res- ers. Scripta mater 57, 117-120. olution electron microscopy (HRTEM). The degree Yan, J., Zhang, G.P., Zhu, X., Liu, H., Yan, C., 2013: of mutual diffusion at the layer interfaces in the Cu/ Microstructures and strengthening mechanisms of Au nanolayered composites under different heat Cu/Ni/W nanolayered composites. Philos Mag 93, treatment conditions was characterized by energy- 434-448. dispersive X-ray analysis (EDX) and HRTEM imaging. Zhang, G.P., Liu, Y., Wang, W., Tan, J., 2006: Experi- Experimental results from nanoindentation show that mental evidence of plastic deformation instability the Hall-Petch (H-P) slope in the relation between in nanoscale Au/Cu multilayers. Appl Phys Lett 88, the strength and the individual layer thickness of 013105. the nanolayered composites gradually decreases Chu, X., Barnett, S.A., 1995: Model of Superlattice with increasing annealing temperature, indicating Yield Stress and Hardness Enhancements. J Appl a decrease in the IBS. TEM examination of the Phys 77, 4403-4411. 196 Talks Topic E 4: Size effects and small-scale mechanical behavior of materials Talks Topic E 4: Size effects and small-scale mechan- ical behavior of materials 197 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Probing thermally activated properties on a local scale Daniel Kiener1, Alexander Leitner1, Verena Maier2 1Montanuniversität Leoben, Department Materials Physics, Austria 2Erich-Schmid Institut for Materials Science, Austrian Academy of Sciences, Leoben, Austria On a macroscopic scale, it is well known that face cro-compression and in-situ TEM indentation experi- centered cubic (fcc) metals can be considered in their ments were performed to get a better understanding athermal limit. However, once the grain size or sam- of the underlying deformation mechanisms. ple size is refined into the sub-micron range, signif- For the fcc Au tested up to 300 °C, we observe that the icant rate dependent material strength is observed. strain rate sensitivity increases with reduced grain size While there is a body of work focussing on these fcc and increasing testing temperature. Interestingly, this materials, little effort was spent on studying thermal- is true for the ultra-fine grained as well as the ultra-fine ly activated mechanisms for body centered cubic (bcc) porous material, indicating that the rate determining metals, which is surprising considering the fact that deformation step is the thermally activated nucleation single crystal samples show a rate dependent behavior and motion of dislocations from grain boundaries, as already on the macroscopic scale. recently already suggested for Cu by Kreuzeder et al.. In this work, we aimed to investigate both, the influ- In case of the bcc Cr, a change in the governing defor- ence of crystal structure and microstructure, respec- mation behavior is observed. First, the presence of tively, on the thermally activated deformation process- grain boundaries leads to a reduction in strain rate sen- es in fcc and bcc metals on a local scale. Therefore, we sitivity for the ufg material compared to the single crys- investigated nanocrystalline, ultra-fine grained, and tal counterpart, which is due to the increased athermal ultra-fine porous Au as representative fcc material, as strength related to the Hall-Petch effect. When increa- well as single crystal and ultra-fine grained Cr as typical sing the testing temperature and finally exceeding the bcc metal, respectively. All fine grained materials were critical temperature of Cr (~180 °C), the strain rate sen- produced by severe plastic deformation, in detail high sitivity of the ufg material increases, while that of the pressure torsion, from their bulk counterparts, or pure single crystal Cr is linearly reduced with testing tempe- powders for the foams, respectively. rature. Thus, above the critical temperature no ther- The local thermally activated deformation behavior mal activation is required for dislocation motion and was studied using advanced nanoindentation testing the bcc Cr essentially behaves fcc-like. techniques at ambient and elevated temperatures using either a Micro Materials or a Keysight system, Reference respectively, where the latter was equipped with a Kreuzeder, M. et al. (2015): Fabrication and ther- continuous stiffness module. Complementary to these mo-mechanical behavior of ultra-fine porous cop- nanoindentation experiments, the bulk material prop- per. JMS, 50: 634643. erties were examined. Miniaturized in-situ SEM mi- Micro- and Macro-mechanical Testing of Grain Boundary Sliding (GBS) Junnan Jiang, Angus Wilkinson, Ricahrd Todd Department of Materials, University of Oxford, United Kindom This project aims to explore the fundamental mecha- vidual grain boundaries to stress by micromechanical nism(s) of grain boundary sliding (GBS) with an empha- tests. Thus, this project is focused on micromechanical sis on its role in superplasticity, using both micro- and tests on microcantilevers and micropillars containing macro-mechanical testing methods. individual grain boundaries. The response of individual Classical models for GBS (Rachinger sliding and Lifshitz grain boundaries will be correlated with grain bound- sliding) assume that all grains and grain boundaries ary characterisation by using electron backscattered undergo the same process, but recent results from re- diffraction (EBSD) to measure the misorientation of search in the group show that this is not true. Individ- the grains on either side of the grain boundary. This ual grain boundaries differ in their ability to participate will link the crystallography of grains to the tendency in sliding and diffusion (Rust and Todd, 2011). There- for GBS. Furthermore, results of micromechanical tests fore, it is important to investigate the response of indi- will be correlated with patterns of GBS seen in poly- 198 Talks Topic E 4: Size effects and small-scale mechanical behavior of materials crystals during macromechanical shear tests. Finally, all with a relatively consistent microstructure. The strain the experimental results will be used to develop mod- rate sensitivity is of great importance to the mecha- els to be implemented in constitutive equations for nu- nism of superplasticity and hence grain boundary slid- merical modelling techniques on GBS. ing. The material chosen was Sn-1%Bi alloy, which is ex- Micro-cantilevers containing individual grain bound- pected to exhibit GBS at room temperature. This is aries have been manufactured for micro-mechanical because the melting temperature of Sn-1%Bi is around tests by nanoindenter. Grain boundaries are character- 504K, while room temperature (298K) is almost 60% ised using EBSD analysis. A few cantilevers have shown of its melting point. Furthermore, it is a single-phase grain boundary sliding along the grain boundary plane alloy, which simplifies the microstructure. The material which is parallel to the displacement direction of the was cold extruded at liquid nitrogen temperature to an nanoindenter (i.e. normal to the sample surface). average grain size of 8.5 µm. Polished samples with this When the grain boundary plane is not parallel to the fine grain size were used in macro-shear tests. Fine, displacement direction or the grain boundary plane is straight surface marker lines were put on the sam- not flat, sliding is inhibited. ple before the test. Surface grids with submicron and coarser pitches were milled by FIB to make quantitative Reference measurements of grain boundary sliding. Macro shear RUST, M. A. & TODD, R. I. 2011. Surface studies of tests were carried out under displacement control at Region II superplasticity of AA5083 in shear: Confir- room temperature. GBS was revealed by the offsets of mation of diffusion creep, grain neighbour switching surface marker lines at the grain boundaries. A stress and absence of dislocation activity. Acta Materialia, ‒ strain rate curve was plotted from a few shear tests 59, 5159-5170. with various strain rates on the same batch of material Nanoindentation at Room and Elevated Temperatures of Au/ Cu-Multilayers Thomas Kreuter1, Guang-Ping Zhang2, Oliver Kraft1, Ruth Schwaiger1 1Karlsruhe Institue of Technology, Institute for Applied Materials, Germany 2Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, People’s Republic of China Thin films and multilayers exhibit strong size effects tion depth, and the thickness changes of the individual in their mechanical behavior such as increasing yield layers were determined. For larger layer thicknesses strength or hardness with decreasing film or layer (100 and 250 nm) the thinning of individual layers was thickness. When the film and layer thicknesses ap- quantified for the measurements at room temperature proach the nanometer scale, the interfaces and grain and at 93°C. A more pronounced layer thinning of the boundaries dominate the deformation behavior. Differ- individual layers was identified for the nanoindents at ent deformation mechanisms have been suggested for 93°C. For the 100 nm layer thicknesses, the top layers different layer thicknesses and types of interfaces such experienced more deformation at both temperatures as dislocation pile-up, confined layer slip or dislocation compared to the 250 nm layers. transmission across the interfaces (Misra 2002). Furthermore, shear bands underneath the indents In this study, Au/Cu-multilayers with individual layer were observed for the thinner layers, as also reported thicknesses in the range from 25 to 250 nm were in- in (Li, 2010). Transmission electron microscopy obser- vestigated at room and elevated temperatures using vation revealed changes of the grain size after the in- nanoindentation. The samples with a total film thick- dentation experiments. ness of 1 µm were prepared using radio frequency In this presentation, the differences in deformation mi- (RF) magnetron sputtering and had a (111) texture in crostructures for the different layer thicknesses will be both Au and Cu layers (Zhang 2006). As expected, the illustrated and discussed in the context of the active hardness and the strain rate sensitivity of the multi- deformation processes. Understanding deformation layers increased with decreasing layer thickness. With and failure of nanoscale multilayers will contribute to increasing temperature the hardness decreased while their future applicability in small-scale mechanical and only small changes in the strain rate senstivity were ob- functional devices. served for temperatures up to 93°C. The deformation microstructures were carefully in- References vestigated by focused ion beam cross-sectioning. The Misra, A., Hirth, J.P. & Kung, H. (2002): Single-disloca- pile-up of material at the sample surface, the indenta- tion-based strengthening mechanisms in nanoscale 199 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 metallic multilayers, Philosophical Magazine A, Vol. multilayers, Applied Physics Letters, Vol. 88, 013105. 82, No. 16, 2935-2951. Li, Y.P. et al. (2010): Investigation of deformation in- Zhang, G.P. et al. (2006): Experimental evidence of stability of Au/Cu multilayers by indentation, Philo- plastic deformation instability in nanoscale Au/Cu sophical Magazine, Vol. 90, No. 22, 3049-3067. Mechanical behavior of the MAX-phase Nb2AlC at the nano- meter and micrometer scale by means of in situ indentation Nadine Schrenker 1, Yonnes Kabiri 1, Mirza Mačković 1, Julian Müller 1, Peter Schweizer 1, Florian Niekiel 1, Björn Hoffmann 2, Silke Christiansen 2,3, Erdmann Spiecker 1 1Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander Universität Erlangen-Nürn- berg, Erlangen, Germany 2Max Planck Institute for the Science of Light, Erlangen, Germany 3Helmholtz Centre Berlin for Materials and Energy, Berlin, Germany MAX phases are layered crystals with ternary or qua- with different orientations, which is a result of the ternary chemical composition. Due to their unique lack of five independent slip systems. In pillars with a set of properties, which is a combination of metallic grain boundary between grains oriented close to the and ceramic attributes, they are in focus of intense re- [0001] and the [10-10] direction final failure occurred search activities. They are excellent electric and ther- by delamination of the basal planes lying parallel to mal conductors, oxidation resistant as well as machina- the surface, which required high stresses. Bending of ble and damage tolerant [1]. As a result of the layered the basal planes oriented edge-on was impeded in this nature of MAX phases, they behave plastically aniso- case by the other grain. Moreover, the compressive tropic. Depending on the orientation the deformation strength measured of the submicron pillars exceeds occurs by a combination of delamination of individual the strength of a bulk material. As the average diame- grains, formation of shear and kink bands. The defor- ter of the pillars at the free end is 0.67 µm, it is possible mation by dislocation glide is assumed to be restricted that dislocation sources get pinned at the surface and to the basal planes. According to Frank and Stroh et al. become single arm sources. The critical resolved shear [2] kink bands are initiated by elastic buckling. Above stress is expected to increase with decreasing source a critical shear stress pairs of dislocations of opposite length (source truncation) [3]. Dislocation escape at sign form and move in opposite direction. By extend- the free surface was observed in other in situ studies ing to the free surface the attraction forces between [4] and could also be an explanation. Furthermore, re- the dislocation walls are eliminated and a kink band is action of nucleated dislocations with preexisting dislo- formed. However, the precise nucleation mechanism cations or FIB induced dislocations can cause paucity of kink bands is not yet known. of available dislocation sources (exhaustion hardening) By means of in situ indentation experiments in the [3]. electron microscope we investigate the mechanical behavior of the MAX-phase Nb2AlC. The preparation References of pillars was performed with a Focus Ion Beam (FIB). [1] M.W. Barsoum and M. Radovic, Annu. Rev. Mater. In the transmission electron microscope pillar com- Res., 41(1):195-227, 2011. pression tests revealed nucleation and propagation of [2] F.C. Frank and A.N. Stroh, Proc. Phys. Soc. B, dislocations on the basal planes with 1/3<11-20> type 65(10):811-821, 1952. Burgers vector. Deformation by basal slip was possible, [3] S.I. Rao, D.M. Dimiduk, T.A. Parthasarathy, M.D. as the basal planes were inclined to the pillar axis. Uchic, M. Tang, and C. Woodward, Acta Mater., Furthermore, the anisotropic behavior was studied 56(13):3245-3259, 2008. by compression tests of submicron pillars in the scan- [4] S. Ho Oh, M. Legros, D. Kiener, and G. Dehm, Nat. ning electron microscope. According to EBSD meas- Mater.,8:95-100, 2009. urements pillars with different orientations were chosen. In the case of single crystal pillars where the Acknowledgements basal planes are parallel to the compression axis, the Financial support by the DFG via research training layers are constrained and forced to delaminate and group GRK 1896 “In situ microscopy with electrons, bend. Post mortem images reveal that the curvature X-rays and scanning probes” is gratefully acknowl- of bending is high as well as slip traces along the basal edged. The authors further thank Prof. Dr. Peter Greil planes. In addition, pillars containing a grain boundary for providing the Nb2AlC samples used in this study. revealed the incompatibility of deformation of grains 200 Talks Topic E 4: Size effects and small-scale mechanical behavior of materials Deformation behavior of copper thin films indented with patterned nanoindenter tips Anke Schachtsiek, Oliver Kraft, Ruth Schwaiger Institute for Applied Materials , Karlsruhe Institute of Technology (KIT), Germany Imprinting or mechanical forming potentially repre- independent of the microstructure. However, the sub- sents a low-cost and high throughput method to pro- strate very clearly influences the imprint patterns and duce high resolution patterns at the micro- and the may lead to delamination, which typically corresponds sub-micrometer scales. Typically the mold is brought to “underfilling conditions” or a high filling factor (Cross into contact with the sample and is then loaded with 2006). The pile-up flows into single peak or dual peak a compressive force for a certain period. In principle, shapes, depending on the cavity width as described for the mold can be used numerous times, ideally with- polymer flow (Rowland 2005). out degradation of the imprint quality. While early In this presentation, the applicability of the imprinting research in this field focused mainly on patterning of method for the direct mechanical forming of micro- soft polymers, more recent studies investigated the and nanoscale metallic structures together with draw- patterning of metals (Lister 2004). However, a stand- backs and limitations will be discussed. ard procedure for metal nanoimprinting has not been established yet. Finding the suitable mold material and References sample mount, choosing load, time and temperature Böhm, J., Schubert, A., Otto, T. & Burkhardt, T. (2001); represent the main challenges. Recently, focused ion Micro-metalforming with silicon dies Microsys. beam and lithographic methods have been adapted Technol. 7, 191-195 successfully for mold fabrication (Lister 2004, Böhm Cross, G.L.W. (2006): The production of nanostruc- 2001). Furthermore, the hardness of a metal depends tures by mechanical forming J. Phys. D: Appl. Phys. on its microstructure affecting the pattern formation. 39, 363-386 For imprint dimensions comparable to the grain size, Durst, K., Hofmann, S., Backes, B., Mueller, J. & Göken, the local flow behavior is poor, limiting the achievable M. (2010): Microimprinting of nanocrystalline met- pattern dimensions (Durst 2010). als - Influence of microstructure and work harden- In this study, the deformation behavior of copper was ing J. Mater. Process. Technol. 210, 1787-1793 investigated. Using a nanoindenter equipped with a Lister, K.A., Thoms, S., Macintyre, D.S., Wilkinson, patterned flat punch tip, a cross-shaped groove was C.D.W. & Weaver, J.M.R. (2004): Direct imprint of created in bulk copper and copper thin films of 800 sub-10 nm features into metal using diamond and nm and 1600 nm thickness on Silicon substrates. The SiC stamps J. Vac. Sci. Technol. B 22 3257–3259 deformation pattern shape was analyzed using atomic Rowland H.D., Sun A.C., Schunk P.R. & King W.P. force microscopy along with scanning electron and fo- (2005): Impact of polymer film thickness and cavity cused ion beam microscopy techniques. size on polymer flow during embossing: toward With respect to the stress-strain relationship, the thin process design rules for nanoimprint lithography J. films exhibit deformation behavior which is apparently Micromech. Microeng. 15 2414–2425 201 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic E 5: Size effects and small-scale mechan- ical behavior of materials 202 Talks Topic E 5: Size effects and small-scale mechanical behavior of materials Using high temperature micromechanical testing to inform microstructure based models: application to IN718 J. Molina-Aldareguia1, B. Gan1, A. Cruzado1, M. Jiménez1, J. Segurado1,2, J. Llorca1,2 1IMDEA Materials Institute, Getafe, Madrid, Spain 2UPM- Universidad Politécnica de Madrid, Madrid, Spain IN718 is widely used in structural applications requir- developed was then evaluated by comparing the sim- ing high strength and toughness [1, 2]. To elucidate ulation of other independent micro-compression tests the underlying mechanisms responsible for the supe- with the corresponding experimental results. rior mechanical properties, a polycrystalline sample of Finally, the extracted plasticity parameters were then IN718 with an average grain size of 150 um was select- used in the numerical simulation of the compression ed for the present investigation. behavior of the macroscopic polycrystalline sample. The grain orientations were analyzed by Electron The agreement was remarkable in all the cases [5]. BackScatter Diffraction (EBSD) and site-specific mi- cropillars with sizes varying from 1 um to 18 um were References machined out by Focused Ion Beam (FIB) milling [3, [1] R Schafrik and R Sprague, Advanced Mater. & Pro- 4],. The micropillars when then tested in compres- cesses 162 (2004) 27–30. sion inside an instrumented nanoindentation system [2] T M Pollock and S Tin, J. Propulsion & Power 22 equipped with a flat punch [5] and the effects of pillar (2006) 361. size, pillar orientation, strain rate and temperature on [3] M D Uchic, D M Dimiduk, J N Florando, WD Nix, the micro- compression behavior were quantitatively Science 305 (2004) 986. assessed. [4] P A Shade, M D Uchic, D M Dimiduk, G B Viswana- The results were used to determine the parameters of than, R Wheeler, H L Fraser, Mater. Sci. and Eng., a single-crystal plasticity (SCP) model of IN718, by com- 535 (2011) 53-61. paring the experimental results with finite element [5] A. Cruzado, B. Gan, H. Chang, K. Ostolaza, A. Lin- (FE) simulations [5]. The calibration of the CP model aza, S. Milenkovic, J. M. Molina-Aldareguia, J. Llorca was done by considering only the plastic contribution and J. Segurado, Int. J. Plast., submitted. of the experimental stress-strain curves. The CP model Multi-scale Fracture Behaviour of Tungsten Alloys for Nucle- ar Fusion BO-SHIUAN LI, DAVID ARMSTRONG, JAMES MARROW, STEVE ROBERTS Department of Materials, University of Oxford, United Kingdom The plasma facing components (PFCs) of the Inter- tungsten has been investigated by Gludovatz et al. [1], national Thermonuclear Experimental Reactor (ITER) reporting a strong dependence on the temperature, divertor will require materials exposed to high heat microstructures, and alloying elements. To gain a deep- flux, neutron damage, and and plasma erosion. Tung- er insight into the fracture behaviour of tungsten on a sten-based alloys are currently the most promising ma- micromechanical basis, the effect of microstructure to terials for the PFCs, due to its superior high tempera- fracture toughness has to be understood. Micro-frac- ture strength, good thermal conductivity, and high re- ture experiments become possible by the combination crystallisation temperature. However, the intrinsic low of focused ion beam (FIB) and nanoindentation. They fracture toughness (KIc) and the high ductile-to-brit- allowed the fracture toughness of single microstructur- tle-transition temperature (DBTT) limit the structural al constituents, such as single grains, grain boundaries, applications of tungsten. Crystalline defects from fu- or shallow irradiated layer to be measured. Tested on sion neutrons and transmutational helium induces sig- very brittle materials, the linear elastic fracture me- nificant hardening/embrittlement and shift the DBTT chanics (LEFM) approach yields reasonable fracture to the low temperature regime. Therefore, multiscale toughness value because the plastic zone under the understandings of the fracture behaviour of tungsten crack tip is small in relation to the specimen size. are required before applying it to fusion applications. Wurster et al. [2] studied the micro-fracture behaviours The macroscopic fracture toughness of polycrystalline of single-crystal tungsten using FIB-fabricated micro- 203 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 cantilevers. The semi-brittle tungsten yields a larger Through extensive FEA and cyclic loading-unloading, plastic zone, therefore the LEFM approach is no lon- crack length at each loading/unloading segment is ob- ger valid, and elastic-plastic fracture mechanics (EPFM) tained. Therefore, fracture toughness can be calculat- has to be applied. In contrast to the brittle fracture ed through the EPFM approach. behaviour seen in macro-sized single-crystal tungsten, Our state-of-the-art hot-stage nanoindenter allows mi- the single-crystal tungsten microcantilevers behave cro-fracture tests to be conducted over a wide range more ductile and exhibit higher fracture toughness. of temperatures (up to 750 °C). For the first time, the The current consencus is smaller is stronger, however fracture behaviour of polycrystalline tungsten can be does this also mean smaller is tougher? characterised at different lengthscale and tempera- In this research, both microcantilevers and macro-scale tures. Through systematic comparisons of results, the four point bending bars with chevron-notches will be mechanical size effects of polycrystalline tungsten to used for fracture tests. By virtue of the chevron geom- fracture toughness can be better understood. etry, crack will form during the early portion of loading and arrests immediately after its formation. Through References a cyclic loading- unloading method, crack is able to [1] E. Gaganidze, D. Rupp, and J. Aktaa, “Fracture be- propagate stably until reaching a critical crack length. haviour of polycrystalline tungsten,” J. Nucl. Mater., Finite element analysis (FEA) is used to select an ef- vol. 446, no. 1–3, pp. 240–245, Mar. 2014. fective chevron geometry that maximizes the stable [2] S. Wurster, C. Motz, and R. Pippan, “Character- crack region, and accurately calculates the stress in- ization of the fracture toughness of micro-sized tensity factor (SIF) along the crack. The EPFM approach tungsten single crystal notched specimens,” Philos. requires detailed information of the crack extension. Mag., vol. 92, no. 14, pp. 1803–1825, May 2012 Effect of composition and morphology on the mechanical and electrical behavior of Cu-Cr thin films Alla. S. Sologubenko1, 2, Wilhelm Hüttenes1, Huan Ma1, Ralph Spolenak1 1Laboratory for Nanometallurgy (LNM), ETH Zürich, Switzerland 2Scientific Center for Optical and Electron Microscopy (ScopeM), ETH Zürich, Switzerland Structural integrity, thermo-mechanical stability and films in both, as-deposited and annealed states, were electrical performance of Cu-Cr thin films on a polymer strained with simultaneous monitoring of the change substrate are studied in this work in uniaxial loading as in film electrical resistance. Tensile tests were carried a function of temperature, phase state and grain mor- out at room temperature and 100oC. phology. Cu and Cr, which are immiscible in thermo- Our studies show a considerably improved electro-me- dynamic equilibrium were magnetron co-sputtered as chanical performance of “columnar” films in compar- thin films of Cu - X at.% Cr (X=5, 10, 20) compositions ison to the “brick-walled”, W- and Ag-modified ones. onto a Kapton substrate. The metastable solid solution We relate this behavior of continuously sputtered films state was aimed in the as-deposited alloys of all three to dense, fine-grained, and in reality non-columnar mi- compositions. Thermal annealing at 300oC for 5h pri- crostructure. The additional electron scattering in the or to straining was performed on films of all compo- “brick-wall” films is considered to be due to the pres- sitions to reveal an effect of phase decomposition on ence of the additional scatter centers, such as Ag- and the microstructure. The films were produced in contin- W-interfaces. The exceptionally good behavior of the uous and interruptive sputtering modes, to yield the Cu-5at.% Cr “columnar” films is related to the truly “columnar” and “brick-wall” grain morphologies. The solid solution state of the metastable alloy. The film “brick-wall”-morphology was achieved by a periodic in- resistivity increases with Cr and the presence of inter- troduction of very thin, less than 2 nm, layers of either layers with Ag being the worst interlayer material. The W or Ag into the body of the film during sputtering. The 100oC-straining increases the plastic range of all films. “columnar”, tungsten-modified and silver-modified 204 Talks Topic E 5: Size effects and small-scale mechanical behavior of materials Thermomechanical influence grinding of electrodeposited chrome coated on a 300M substrate Benjamin Weiss1, André Lefebvre², Olivier Sinot², Albert Tidu1 1LEM3 - Laboratoire d’Etude des Microstrucutres et de Mécanique des Matériaux, Metz, France 2LABPS, Laboratoire de mécanique Biommécanique Polymère et STructure, Metz, France Hard chromium coating is a commonly used material microstructural observations, thermally and mechan- for industrial application. It is obtained by the well-es- ically sub-surface are observed. tablished electrodeposition technique, These coatings For the 300M steel substrate, damage were observed are mainly applied for the production of functional even in the subtrate according to the grinding condi- coatings on engineering components in view to en- tion. The various characterization tools have been used hance their wear, hardness and corrosion resistance to characterize the damage of the substrate. Trans- properties. verse microscopy observation shows the influence of Grinding is a material removal operation widely used the heat flux through the coating : mainly reduction or in manufacturing industry. It’s well known that grind- increase in hardness or over-tempering of the material ing generates significant deformation and friction com- and metallurgical change such martensitic transforma- pared to other machining processes. The combination tion. of material removal, elastoplastic deformation and fric- To support these tests and to explain the observed tion can transform the surface workpiece. There may variation both in metallurgical changes and hardness be the creation of cracks, the occurrence of burning values, finite element simulations were conducted to traces on the workpiece or hardness and stress varia- understand the spread of the heat flux and the to cor- tion (Papatheodorou 2005), (Lescalier 2002), (Sorsa et relate temperature variations with the observed states al, 2011). of the material. These simulation are conducted using The present study reports results obtained in grinding FEM analysis and are based on the moving heat source of electroplated chromium coatings on a steel sub- (Lefebvre, 2012). strate 300M (a high strength steel substrate obtained after thermal treatment). Although the grinding con- References cerne only the chromium coating. Lescalier, C., Arzur, J., Martin, P. & Bomont, O. (2002). Several tests were performed to achieve various levels Interactions pièce–outil–machine en rectification. of heat transfer across the coating. The main operat- Détermination rationnelle du domaine de fonction- ing parameters are the wheel speed, the workpiece nement. Mécanique & Industries, 3(4), 351–360. speed and the depth of cut. After each test, chromium Papatheodorou, T. & Hannifin, P. (2005). Influence of coating and substrate have been characterized using hard chrome plated rod surface treatments on seal- mechanical analysis and microstructural analysis or ob- ing behavior of hydraulic rod seals, Sealing Technol- servations : optical microscopy coupled with hardness ogy (April), 5–10. measurement, SEM for the observation of crack and Sorsa, A., Leiviskä, K., Santa-aho, S. & Lepistö, T. grain morphology, XRD for residual stresses and crystal- (2012). Quantitative prediction of residual stress lographic texture analysis, Nital etching and Barkhaus- and hardness in case-hardened steel based on the en noise for metallurgical transformation). Some of Barkhausen noise measurement, NDT & E Interna- these analysis are applied to the substrate and/or to tional, Vol 46, 100-106. the coating, depending on the measured property. Lefebvre, A., Lanzetta, F., Lipinski, P., Torrance, A.A. For the chromium coating, the main result is a clear (2012) Measurement of grinding temperatures us- description of a chromium burned surface. High stress- ing a foil/workpiece thermocouple, International es and crystallographic texture gradient are observed Journal of Machine Tools and Manufacture, Vol 58 depending on the grinding conditions. Supported by (July), 1-10. 205 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Orthogonal machining of a Cu-1.8wt%Be-0.1wt%Co alloy: influence of the microstructure Alban De Saever, Albert Tidu LEM3 - Laboratoire d’Etude des Microstrucutres et de Mécanique des Matériaux, Metz, France Elucidating the effect of microstructure is one of the cutting speed (1 m.s-1), but for multiple depths of cut in main challenge in the field of material machining re- a range from 2 to 40 µm. A Kistler dynamometer table moval (Leopold, 2014). For this purpose, copper-beryl- was used to measure cutting forces. The friction coef- lium samples with different microstructures has been ficient (Tangent Force / Normal Force) was deduced submitted to orthogonal cutting. The results show the for each material. As a result, for an increase of pri- microstructure impact on the mechanical behaviors or deformation, the friction coefficient decrease until during the cutting process. a minimum value. This trend is clearly noticeable for Studies on the mechanisms that rule the age-harden- micro-cutting, and is stronger for an increase of depth ing of a C17300 (Cu-1.8wt%Be-0.1wt%Co) alloy using of cut. Orthogonal cutting produced serrated continu- cold-working and/or specific heat treatments high- ous chips for each material. SEM observations of the lighted the sequence of precipitation. Earliest develop- serrated chips show adiabatic shear bands, cracks and ments showed equivalent sequences (G.P. zones → γ’’ drastic changes of the phases composition (confirmed → γ’ → γ) for many authors (Geisler, 1952 - Bonfields, by TEM observations), these observations are clearly 1974) but reported distinct crystallographic structures. dependent on the cutting conditions. Latest developments (Monzen, 2012) clarified those Temperature measurement using a special device in- observations and described the accurate following se- cluding intrinsic thermocouple has shown that temper- quence (G.P. zones → γ’’ → γ’I → γI + γ’ → γ) by com- ature rise near the cutting edge tool is about 1050K. bining results from heat treatments and stress-assisted The results highlight that the observed differences dur- nucleation. ing orthogonal cutting are directly correlated to the in- Strength hardening of C17300 alloys is mainly depend- itial microstructure and its evolution during cutting. A ent on the ageing time and cold-working. By adjust- model including the mechanical behavior of the initial ing the couple cold-working (cold-rolling from 0 up to strengthened material and the topology of the plate- 1.61 true strain)/duration of heat treatment (0 up to 1 lets, in conjunction with thermal reversion is proposed hour at constant temperature 573K), 5 samples with in view to explain the observed trend. different microstructures with equivalent hardness (350 HV20) have been manufactured. A very detailed References multi-scale analysis (SEM-TEM-XRD) on those samples Leopold, J. (2014): Approaches for modelling and sim- showed that various microstructures were present in ulation of metal machining – a critical review, Man- terms of phases, grain size and particles or plate-like ufacturing Rev. 2014, 1, 7 topology. SEM observations revealed that the domain Geisler, A. H., Mallery, J. H. & Steigert, F. E. (1952): On size of inter-granular γ-phase decrease drastically re- the Mechanism of Precipitation In Copper-Beryllium spect to the increase of initial deformation. Even if mor- Alloys - Journal of Metals, March 1952, 307-316; phologies of intra-granular phases are always coherent Transaction AIME. plate-like precipitates, TEM observations showed their Bonfields, B. & Edwards, B. C. (1974): Precipitation distribution, length and width were variable with dif- hardening in Cu 1.81 wt% Be 0.28 wt% Co - Journal ferent thermo-mechanical treatments. Phases quanti- of Materials Science 9, 1974, 398-408; Chapman fication were done through X-Ray Diffraction and crys- and Hall Ltd. tallographic texture of the solid solution α-CuBe were Monzen, R., Okawara, S. & Watanabe, C. (2012): obtained by EBSD analysis. Stress-assisted nucleation and growth of γ’’ and γ’ Using homemade carbide tools with cutting edge radi- precipitates in a Cu-1.2 wt% Be-0.1 wt% Co alloy us under 2 µm, true orthogonal machining on samples aged at 320°C - Philosophical Magazine, Vol. 92, with equivalent hardness and different microstructures No.14, 11 May 2012, 1826-1843; Taylor&Francis. has been achieved for a unique cutting geometry and 206 Talks Topic E 6: Size effects and small-scale mechanical behavior of materials Talks Topic E 6: Size effects and small-scale mechan- ical behavior of materials 207 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Grain size gradient-induced work hardening and extraordi- nary ductilization Xiaolei Wu 1, Yuntian Zhu 2 1 State Key laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China 2 Department of Materials Science and Engineering, North Carolina State University, Raleigh, USA Strain hardening is critical for structural materials to ous strain hardening rate up-turn. Such a unique ex- secure desired ductility, especially for high-strength tra strain hardening inherent to the GNG structures, metals that often suffer from poor ductility. Here we which does not exist in homogeneously-structured report that the gradient nano-grained (GNG) surface materials, provides a novel strategy to develop strong- layers sandwiching a coarse-grained core render an and-ductile materials by architecturing heterogeneous extra strain hardening. The grain size gradient in the nanostructures. The work uncovers the intrinsic large nano-micro-scale induced a notable strain gradient uniform tensile elongation of the nanostructures and under tension that converts the applied uniaxial stress paves the way toward a combination of high strength to multi-axial stresses. Thereby the accumulation and and good ductility for their structural application. interaction of dislocations are promoted in the GNG layers, resulting in an extra hardening and an obvi- Mechanical properties and microstructural changes of high strength AA7075 alloy during low temperature ECAP Sebastian Fritsch, Mario Scholze, Martin F.-X. Wagner TU Chemnitz, Institute of Materials Science and Engineering, Germany High strength aluminum alloys are generally hard to demonstrate how these thermo-mechanical processes deform. Therefore, the application of conventional se- affect the microstructure and the mechanical behavior vere plastic deformation methods to generate ultraf- of the resulting materials under high strain rates. Our ine-grained microstructures and to further increase results highlight the potential of forming at low tem- strength is considerably limited. In this study, we ex- peratures to produce high-strength aluminum alloys plore cryogenic deformation in a custom-built, cooled with improved properties after severe plastic deforma- equal channel angular pressing (ECAP) tool (internal tion. angle 90°) as an alternative approach to severely plas- tically deform a 7075 aluminum alloy. We characterize References the mechanical behavior and the microstructure of the Fritsch, S., Hunger, S., Scholze, M., Hockauf, M. & coarse grained base material at different low temper- Wagner, M. F.-X. (2011): Optimisation of thermo atures, and we analyze how a tendency for the PLC-ef- mechanical treatments using cryogenic rolling fect and the strain hardening rate affect the formability and aging of the high strength aluminum alloy during subsequent severe plastic deformation at low AlZn5.5MgCu (AA7075). – In: Materialwissenschaft temperatures. We also demonstrate that low-tempera- und Werkstofftechnik, 42: 573-579, Weinheim ture ECAP followed by suitable heat treatments results Fritsch, S., Scholze, M. & Wagner, M. F.-X. (2012): Cry- in increases of the attainable degree of deformation, ogenic forming of AA7075 by Equal-Channel Angular strength and ductility. We show how pre-aging treat- pressing. – In: Materialwissenschaft und Werkst- ments at room temperature prior to ECAP can be used offtechnik, 43: 561-566, Weinheim to influence the grain refinement process. Finally we 208 Talks Topic E 6: Size effects and small-scale mechanical behavior of materials Effect of creep and aging on the precipitation kinetics of an Al-Cu-Alloy after ECAP Markus Härtel1, Kevin G. Abstoss2, Swetlana Wagner1, Philipp Frint1, Peter Mayr2, Martin F.-X. Wagner1 1TU Chemnitz, Institute of Materials Science and Engineering, Germany 2Professorship of Welding Engineering, TU Chemnitz, Germany Recent work has shown that severe plastic deforma- constant, the influence of temperature is investigat- tion processes such as equal-channel angular pressing ed. Special care is taken to characterize the types and (ECAP) or high pressure torsion accelerate the precipi- morphologies of precipitates in the aged or crept sam- tation kinetics of Al-Cu-alloys. In this study, we analyze ples using transmission electron microscopy. Our study how a combination of mechanical load, aging time and shows that increasing mechanical loads accelerate the aging temperature affects the precipitation kinetics of precipitation kinetics by increasing dislocation density an AA2017 alloy after ECAP. After solution annealing, (and thus providing more opportunities for nucleation the material is deformed in one pass in a 120° ECAP of the precipitates). Temperature accelerates the pre- tool at 140°C. Compressive creep tests (which repre- cipitation kinetics as well and results in coarser precip- sent a combination of mechanical load, aging time and itates. Different creep times can lead to the formation aging temperature) are performed on the initial (pre- of two different regions in the microstructure: regions ECAP) condition and on the ECAP-deformed material, with only few coarsened S-phase precipitates, and re- and the resulting microstructures are compared using gions with many, fine S-phase precipitates. This evolu- electron microscopy. To differentiate between the ef- tion into different microstructural zones can be directly fects of mechanical loads, (aging) temperatures and related to the heterogeneity of ECAP deformation pro- times, the experimental parameters are selected care- duced in a single pass. Our study provides important fully: To investigate the influence of the mechanical information on how creep and aging of SPD-deformed, load, stopped compressive creep tests are performed thermodynamically instable Al-Cu-alloys affects their and compared with aging conditions (without any precipitation kinetics, and it indicates that applications mechanical load) at the same temperature and after of ultra-fine grained materials need to be limited to rel- the same amount of time. By keeping, in another set atively narrow temperature windows. of stopped compressive creep tests, time and load On shear localization in an SPD-processed Aluminum Alloy – Part 1: Microstructures and local mechanical properties Philipp Frint, Steffen Pfeiffer, Martin F.-X. Wagner TU Chemnitz, Professur Werkstofftechnik, Chemnitz, Germany In this study, we report on the observation of heter- measurements and nanoindentation jump-tests are ogeneous microstructures after processing of the performed to explore the characteristics of the defor- aluminum alloy 6060 by extrusion and subsequent mation bands. In addition to different hardness values, equal-channel angular pressing (ECAP) at room tem- caused by the different deformation induced strain perature. A macroscopic, alternating structure of hardening, the ultrafine-grained shear bands exhibit a two types of bands is observed: shear bands carrying considerably increased strain rate sensitivity (by a fac- large amounts of deformation are located next to ma- tor of more than 2) compared to the matrix bands. A trix bands that contain significantly less deformation. comparison of the initial extruded microstructure with Scanning (SEM) and transmission (TEM) electron mi- the ECAP-processed material reveals that simple shear croscopy reveal an ultrafine-grained microstructure deformation exclusively takes place within the shear in the shear bands, while the microstructure of the bands while the matrix bands pass through the ECAP- matrix bands is characterized by a high fraction of low die without getting sheared. This observation contra- angle grain boundaries and dislocation cells. These dicts the simple theory of homogeneous simple shear characteristic microstructural features affect the local during ECAP-processing; we propose a simple mechan- mechanical properties, which are found to be distinctly ical model describing the evolution of the band-struc- different for the two types of bands. Micro-hardness ture, based on an alternating interplay of elastic and 209 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 plastic deformation inside the shear zone driven by rial. In a companion presentation at this conference, local microstructure-dependent softening of the mate- we analyze this mechanical model in detail using nu- On shear localization in an SPD-processed Aluminum Alloy– Part 2: A simple model concept and FE simulation of the formation of alternating bands Steffen Pfeiffer, Philipp Frint, Martin F.-X. Wagner TU Chemnitz, Professur Werkstofftechnik, Germany Equal-channel angular pressing (ECAP) is a method of (FE) simulations with an elasto-plastic material model, severe plastic deformation that typically leads to a ho- we identify engineering factors that directly influence mogeneous simple shear deformation and that is used the local deformation behavior. Our model predicts to produce ultrafine-grained microstructures. In some that, prior to reaching the yield stress, a well-defined special cases, however, single ECAP passes result in the material volume passes through the shear zone simply formation of heterogeneous microstructures; this was, by elastic deformation – and this process results in the for example, observed in a companion study where formation of matrix bands adjacent to the shear bands. the formation of alternating types of shear and matrix We analyze how varying inner channel radii and cross bands were observed after ECAP of an aluminum alloy sectional areas of the ECAP billet affect displacement-, 6060. Both microstructural features and mechanical strain-, strain-rate- and stress-fields in the shear zone. properties (determined by micro- and nanoindenta- Our results show that the largest equivalent stresses tion) demonstrate that the ECAP shear deformation arise at the inner-channel corner, where consequently is concentrated in shear bands, whereas the adjacent the formation of shear bands is triggered. Increasing matrix band regions are hardly deformed. In this con- inner-channel radii lead to larger elastic displacements tribution, we present a simple mechanical model to and to wider matrix bands, and the predictions on rationalize how a discreet material volume can pass shear band morphologies and dimensions are in good the shear zone of the ECAP die without accumulating agreement with our experimental observations. These significant amounts of plastic shear deformation, and results contribute to a more detailed understanding of how this process results in the alternating formation of the locally heterogeneous deformation of pre-extrud- matrix and shear band regions. Using 2D finite element ed or heavily work hardened materials during ECAP. 210 Talks Topic E 7: Size effects and small-scale mechanical behavior of materials Talks Topic E 7: Size effects and small-scale mechan- ical behavior of materials 211 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Bio-inspired, self-assembled functionalized Fe3O4 nanoparti- cles with tunable machanical properties Gerold A. Schneider1,, Axel Dreyer1, Artur Feld2, Ezgi Yilmaz1, Andreas Kornowski2, Tobias Krekeler3, Heshmat Noei 4, Martin Ritter3, Andreas Stierle4, Hosrt Weller2 1Institute of Advanced Ceramics, Hamburg University of Technology, Germany 2Institute of Physical Chemistry, University of Hamburg, Germany 3Electron Microscopy Unit, Hamburg University of Technology, Germany 4Research Group X-ray Physics and Nanoscience, Deutsches Elektronen-Synchrotron DESY and Physics Depart- ment, University of Hamburg, Germany Nature’s hard tissues are typically hierarchical materi- this principle to self-assembled 10-20nm – sized Fe3O4 als with a brick and mortar like structure consisting of particles functionalized with short ligands. By changing hard minerals surrounded by soft organic matter. In na- the organic ligands it is possible to tune the strength cre or enamel the organic content is as low as 15 Vol.% and elasticity of these hybrid-materials in ranges or even less, which makes these biological materials where they compete with metals and polymers. The very hard and stiff while retaining an amazing tough- cross-linking and grafting of the molecules was evalu- ness. It seems that one of the keys of this design con- ated by XPS and FTIR measurements. The arrangement cept is based on nature’s ability to build up its materials of the particles in grain-like superstructures was inves- from nanometer sized minerals. We therefore applied tigated by SAXS and TEM measurements. In situ SEM compression tests of layered crystals PETER SCHWEIZER, FLORIAN NIEKIEL, ERDMANN SPIECKER Center for Nanoanalysis and Electron Microscopy (CENEM), University of Erlangen-Nürnberg, Erlangen, Germany Layered crystals have gained a lot of attention in ma- In this work we present a method to test the slip of terials science in the recent years due to their quasi basal planes in layered crystals on the example of two-dimensional structure which gives rise to a pleth- graphite and vanadium diselenide (VSe2). A modified ora of outstanding properties. Certainly the most version of the established micro-pillar compression well-known example for such a material is graphite test introduced by Uchic et al.5 was established that which can be broken up into its single layers known uses the inclination angle of the pillars to achieve the as graphene1. Another class of materials that is simi- desired crystallographic orientation of the material rel- lar in structure and can also be exfoliated into single ative to the compression axis. An FEI Helios Nanolab layers are the transition metal dichalcogenides, which 660 DualBeam has been used for both sample prepa- show many extraordinary properties such as semicon- ration and in situ compression of the studied pillars. ductivity, superconductivity or the formation of charge The indentations were performed in situ enabling a density waves2. Besides the electronic properties, the deeper analysis of the deformation process. Force and mechanical properties of layered crystals are highly in- displacement data was recorded using a combination triguing because they show an extreme case of anisot- of a spring table system and digital image correlation. ropy. The strong inner-layer bonds are in stark contrast During indentation slip along a single atomic interface with the weak van-der-Waals type interlayer bonds. was achieved consistently. TEM lamellas of deformed This results in extreme strength for single layers, as it pillars have been prepared in cross-section and plan was shown for graphene with a Young’s modulus of up view of the slip interface to obtain further insights into to 1 TPa3, while at the same time making a bulk sample the deformation behavior and characterize the damage comprised of many layers very deformable through the induced into the material by the preparation with the mechanism of basal slip. One technological application focused ion beam. The presented method enables the that arises due to these properties is solid lubrication4. quantification of the friction forces at a single atomic A deeper understanding of the exact mechanisms of interface within a layered crystal. Further experiments basal slip and the quantification of the forces neces- will deal with more complex materials like the misfit sary to induce slip is required for future applications of layer compounds to also investigate the elusive effect layered crystals in advanced mechanical devices. of superlubricity at incommensurate interfaces. 212 Talks Topic E 7: Size effects and small-scale mechanical behavior of materials References 4. Winer, W. O. Molybdenum disulfide as a lubricant: 1. Novoselov, K. S. et al. Electric Field Effect in Atom- A review of the fundamental knowledge, Wear 10, ically Thin Carbon Films, Science 306, 666–669 422–452 (1967). (2004). 5. Uchic, M. D. Sample Dimensions Influence Strength 2. Wang, Q. H. Kalantar-Zadeh, K. Kis, A. Coleman, J. and Crystal Plasticity, Science 305, 986–989 (2004). N. & Strano, M. S. Electronics and optoelectronics of two-dimensional transition metal dichalcogenides, Acknowledgements Nature Nanotech 7, 699–712 (2012). Financial support by the DFG via the research training 3. Lee, C. Wei, X. Kysar, J. W. & Hone, J. Measurement group GRK 1896 “In situ microscopy with electrons, of the Elastic Properties and Intrinsic Strength of X-rays and scanning probes” is gratefully acknowl- Monolayer Graphene, Science 321, 385–388 (2008). edged. Material development for high-strength nanocomposites Almut Schroer, Jens Bauer, Oliver Kraft Institute for Applied Materials, Karlsruhe Institute of Technology, Germany Further development of materials with low density and substrates have been performed in order to determine high strength is of great interest for lightweight appli- Young’s modulus and hardness of the ALD coatings. For cations. Technical foams are highly porous materials instance, the Young’s modulus of a 100 nm thick alumi- which possess a very low density but at the same time na film was determined to be 171 GPa with a standard only a low strength due to their random architecture. deviation of 12 GPa, and the hardness to be 12.2 GPa The macroscopic material properties of cellular mate- with a standard deviation of 1.5 GPa, respectively. Ob- rials are strongly influenced by the characteristics of viously, the measured modulus is well below that of their architecture. Moreover, if the dimensions of the bulk alumina but in line with earlier measurements of cellular materials reach the nanoscale, the materials ALD coatings (Tripp 2006). Promising coating materials benefit of the mechanical size effect with an improved are further examined using a novel technique based strength and should become less sensitive to flaws on push-to-pull structures, which are fabricated in the (Gao 2003). same manner as the composites themselves. The test Using 3D direct laser writing in combination with structures allow for tensile tests of the nanocompos- atomic layer deposition (ALD), the fabrication of alumi- ites. The whole specimens are manufactured in one na-polymer composites with 3D microarchitecture has direct laser writing step. First results show increasing been demonstrated (Bauer 2014). The composites are strength for decreasing alumina layer thickness be- constructed as polymer microstructures with diame- tween 10 and 100 nm. Also, the role of the thermal ters of 0.5-1.0 µm, coated with thin layers of aluminum treatment of the polymeric microstructures during ALD oxide within the range of 10 to 100 nm. In this way, is examined. it was possible to exploit both the structural advan- tage of ordered frameworks with optimized architec- ture and the size-dependent strengthening effect. As References a result, the nanocomposites exceed the strength-to- Gao, H. et al. (2003): Materials become insensitive weight ratio of other engineering foams. However, the to flaws at nanoscale: Lessons from nature. – Proc. potential for improving the strength of such structures Natl. Acad. Sci. 100 (10): 5597-5600; USA by using different coating materials and coating tech- Bauer, J. et al. (2014): High-strength cellular ceramic niques as well as by further treatments of the polymer- composites with 3D microarchitecture. – Proc. Natl. ic microstructures after the laser writing step, has not Acad. Sci. 111 (7): 2453-2458; USA been examined. Tripp, M. K. et al. (2006): The mechanical properties It is the aim of the work to improve the strength of of atomic layer deposited alumina for use in micro- the nanocomposites due to further development of and nano-electromechanical systems. – Sensors and the used materials. Nanoindentation measurements Actuators A 130-131: 419-429 on thin films of different ceramic ALD coatings on Si 213 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Mechanical behavior of ultrathin aluminum oxide films: Influence of open or closed porosity A. van der Rest, F. Henry, A. Favache, J. Proost, Q. Van Overmeere, T. Pardoen Institute of Mechanics Material and Civil Engineering, Université Catholique de Louvain, Belgium Native Al2O3 affects the mechanical response of me- correlates with the increasing porosity of the films. The tallic Al thin films. However, the lack of knowledge re- stress to failure also decreases with increasing porosi- garding the dependence of intrinsic stiffness, strength ty. The precise influence of open porosity fraction and and ductility of Al2O3 on its microstructure and of the pore dimensions on the Young’s modulus and stress to complex mechanical behavior of the Al/Al2O3 interface failure will be presented. Differences between open limits the understanding and control of the mechanical and closed porosities will be highlighted. reliability of Al thin films. [1] In this research, we first explore the dependence of the mechanical properties of Al2O3 films on its microstruc- ture, focusing on the effect of porosity. Ultrathin Al2O3 films encompassing a range of characteristic porosities were produced by reactive magnetron sputtering (ran- dom closed porosities) and anodic oxidation (ordered open porosities) as illustrated in figure 1. Fig. 2: Stress-strain response of the Al2O3 thin films pro- duced by reactive magnetron sputtering at different depo- sition pressures, characterized with the “on-chip” uniaxial nanomechanical testing. We will further consider how controlling the porosity Fig.1: Two processes are used to produce ultrathin Al2O3 allows to design mechanically robust multilayered Al/ thin films: the anodic oxidation produces films with open or- Al2O3 applications. The first investigations, using na- dered porosities and the reactive magnetron sputtering pro- no-indentation, regarding the strength and ductility of duces films having random closed porosities. Al/Al2O3 thin multilayers with various thickness ratios will be presented and compared to thin films of Al and The Young’s modulus of the films was determined by Al2O3. nano-indentation and compared to the stress strain re- sponse characterized with “on-chip” uniaxial nanome- References chanical testing [2] (see figure 2), providing additional [1] A. T. Alpas, J. D. Embury, D. A. Hardwick, R. W. insights on fracture. The Young’s modulus measured Springer, J. Mater. Sci. 25, 1603 (1990). by on-chip testing are in good agreement with the val- [2] S. Gravier, M. Coulombier, A. Safi, N. André, A. Boe, ues obtained by nano-indentation. Considering for in- J.-P. Raskin, T. Pardoen, J. Microelectromech. Syst. stance films with random closed porosities, the Young’s 18, 555 (2009). modulus decrease with increasing deposition pressure 214 Talks Topic E 7: Size effects and small-scale mechanical behavior of materials Influences of vacancy defects on compressive behaviors of open-tip carbon nanocones Ming-Liang Liao Department of Aircraft Engineering, Air Force Institute of Technology, Taiwan Since carbon nanocones (CNCs) have similar structures strain and in the critical load with the CNC with a mid- and properties to those of carbon nanotubes (CNTs), dle vacancy, whereas the CNC with a lower vacancy has applications of such nanomaterial have developed lower degradation in the anti-buckling ability than the considerably in recent years (Tagmatarchis 2012). above two CNCs. The anti-buckling ability of the CNCs While there is considerable achievement in studies reduces with the growth of the temperature. This tem- of mechanical behaviors of CNCs, studies on mechan- perature effect is much apparent in the perfect CNC ical behaviors of CNCs with defects (such as vacancy than in the vacancy-defect CNCs. It was also observed defects) are deficient. This topic is very important as that the degradation in the anti-buckling ability is ob- the practical applications of CNCs are explored largely. vious at a lower temperature, but it decreases as the Moreover, defects in CNCs can appear at the stage of temperature grows. Besides, all the CNCs (including their growth/purification as well as during their device the perfect and the vacancy-defect CNCs) exhibited a production, and can be created deliberately by chem- shrinking/swelling buckling mode shape at the studied ical treatments or by irradiation to achieve desired temperatures. Existence of the vacancies did not alter functionalities, as those occurring in CNTs (Andrews the buckling mode shape of the CNCs. et al. 2001; Ni and Sinnott 2000). Therefore, is worthy to understand influences of defects on mechanical be- References haviors of CNCs. In contrast to the plentiful studies on Andrews, R., Jacques, D., Qian, D., and Dickey, E. C. mechanical behaviors of CNTs with defects, investiga- (2001): Purification and structural annealing of mul- tions into this topic for CNCs are rare in the available tiwalled carbon nanotubes at graphitization tem- literature. To fill in this deficiency and provide some peratures. Carbon, 39: 1681-1387. information for the practical applications of CNCs, this Liao, M. L., Cheng, C. H., and Lin, Y. P. (2011): Tensile paper extended the author’s previous studies (Liao et and compressive behaviors of open-tip carbon al. 2011; Liao 2014) to examine influences of vacancy nanocones under axial strains. J. Mater. Res., 26: defects on compressive behaviors of open-tip CNCs. Ef- 1577-1584. fects of vacancy location and temperature on the com- Liao, M. L. (2014): Buckling behaviors of open-tip pressive behaviors were inspected in this study. carbon nanocones at elevated temperatures. Appl. This study investigated influences of vacancy defects Phys. A, 117: 1109-1118. on compressive behaviors of open-tip carbon nano- Ni, B. and Sinnott, S. B. (2000): Chemical functionaliza- cones (CNCs) by molecular dynamics simulations. tion of carbon nanotubes through energetic radical Effects of vacancy location and temperature on the collisions. Phys. Rev. B, 61: R16343. compressive behaviors were examined in the study. Tagmatarchis, N. (editor) (2012): Advances in Carbon Some interesting findings were attained from the in- Nanomaterials: Science and Applications. Pan Stan- vestigations. It was noticed that the CNC with an up- ford Publishing. per vacancy has comparable degradation in the critical 215 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 TalksTopic E 8: Size effects and small-scale mechan- ical behavior of materials 216 Talks Topic E 8: Size effects and small-scale mechanical behavior of materials Size Effect of Single Crystalline Noble FCC Metal Nanowires In-Suk Choi Thigh Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul, Republic of Korea Researchers have known for some time that smaller is rhombic to square through long-ranged, coherent twin stronger for both nanocrystalline materials, and more propagation, which occurs by a concurrent reorienta- recently one-dimensional (1D) nanostructures such as tion of the bounding surfaces from {111} to {100}. Im- nanowires. However, an elusive but fundamentally im- portantly, the ductility is not reduced with an increase portant goal is to find 1D nanostructures that are both in strength, where both the nanowire yield and twin strong and ductile. In this work, we demonstrate how propagation stresses increase with decreasing nanow- surface effects enable this important combination of ire diameter. A simple surface energy differential model properties by experimentally applying tensile deforma- is found to capture the inverse diameter-dependence tion to rhombic cross section Au, Pd and AuPd nanow- of the twin propagation stress, further highlighting the ires that have a <110> orientation and four bounding importance of surface effects in enhancing the size-de- {111} transverse surfaces. We show that high ductility, pendent mechanical behavior and properties of metal and fracture strains of about 50% are obtained through nanowires. a geometric reorientation of the cross section from Mechanical Behavior of Fivefold Twinned Nanowires under- stood from Anisotropic Elasticity Florian Niekiel1, Erdmann Spiecker1, Erik Bitzek2 1Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander-Universität Erlangen-Nürn- berg, Erlangen, Germany 2Department of Material Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlan- gen, Germany Metallic nanowires are currently attracting a lot of in- ires. This size-independent effect can be readily under- terest. On the one hand they show promising electrical, stood from theoretical considerations based on aniso- optical and mechanical properties for applications in tropic elasticity. We develop a simple analytical model transparent electrodes and flexible electronics, on the which correctly describes the systematic trend seen in other hand they represent an ideal model system to the change of elastic modulus of fivefold twinned na- challenge our understanding of the relation between nowires simulated for different materials (Al, Au, Ni, microstructure and mechanical properties. Most me- Ag, Cu). tallic nanowires grown from wet chemical synthesis Moreover, our results show that also the plastic defor- exhibit a distinctive fivefold twinned microstructure mation of fivefold twinned nanowires is to a large consisting of five segments sharing a common [110] degree influenced by anisotropic elasticity. Depend- direction along the nanowire axis and joined by twin ing on the material, the fivefold twinned microstruc- boundaries in cross sectional direction. The remaining ture can lead either to an increase or decrease of the gap of 7.35° is closed by strain corresponding to a cen- yield stress compared to single crystalline nanowires. tral positive partial wedge disclination. In simulations of tensile tests a change of the failure In this work atomistic simulations and finite element mechanism to void formation instead of necking can analysis are employed to elucidate the fundamental be observed depending on the anisotropy factor of the difference in the mechanical properties of fivefold material. In compression tests structural dislocations twinned nanowires compared to their single crystalline are found to relieve the intensifying stress state due counterparts. To achieve this, size effects due to sur- to the disclination. The different deformation mecha- face stresses and different surface stiffness are careful- nisms and yield stresses can be readily explained using ly analyzed and discriminated from the size-independ- the developed analytical model. ent elastic response. Our main result is that the microstructural constraint Acknowledgments of the fivefold twinned microstructure leads to an elas- Financial support by the DFG via research training tic response of these nanowires that is fundamentally group GRK 1896 is gratefully acknowledged. different from the elasticity of single crystalline nanow- 217 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Mechanical properties of nano-twinned Ag wires Aaron Kobler1,2, Thorsten Beuth3, Tobias Klöffel4,5, Markus Moosmann1,6, Horst Hahn1,2, Christian Kübel1,7, Bernd Meyer4, Erik Bitzek5, Thomas Schimmel1,6 1Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), Germany 2Joint Research Laboratory Nanomaterials (KIT and TUD), Technische Universität Darmstadt (TUD), Germany 3Institute for Information Processing Technologies, Karlsruhe Institute of Technology (KIT), Germany 4Interdisciplinary Center for Molecular Materials (ICMM) and Computer-Chemistry-Center (CCC), Friedrich-Alex- ander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany 5Materials Science & Engineering, Institute I, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany 6Institute for Applied Physics, Karlsruhe Institute of Technology (KIT), Germany 7Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), Germany The production and investigation of nano wires is a glide systems active in fcc metals and the stress direc- vivid topic, as nano wires exhibit superior mechanical tion are discussed to explain indentations orthogonal properties such as high tensile strength1. These prop- (<111> direction) or parallel (<110> direction) to the erties make them a perfect candidate for applications twin boundaries Furthermore, density functional the- in micro-mechanical systems (MEMS). For bulk materi- ory and atomistic calculations were performed as a als, it is well known that a decreased grain size results reference for the NWs and showed no influence of the in an increased material’s strength (Hall-Petch relation twin boundaries on the Yong’s modulus in direction of (HP))2. Introducing nanotwins into a material can in- the wires axis. crease the ductility while maintaining a high strength3. On the other hand, little is known about tuning the References microstructure of nanowires (NW). Calculations on 1. Weinberger, C. R. & Cai, W. Plasticity of metal nano- twinned Cu NWs showed that the strengthening ef- wires. J. Mater. Chem. 22, 3277 (2012). fects seen in bulk materials can be transferred to NWs. 2. Meyers, M. A., Mishra, A. & Benson, D. J. Mechan- However, the strengthening effect is highly shape and ical properties of nanocrystalline materials. Prog. microstructure dependent4. Mater. Sci. 51, 427–556 (2006). Here, we present Ag NWs with twin planes parallel 3. Stukowski, A., Albe, K. & Farkas, D. Nanotwinned to the wire long <112> axis. A model for the growth fcc metals: Strengthening versus softening mecha- mechanism is suggested to explain the observed <112> nisms. Phys. Rev. B 82, 1–9 (2010). growth direction. The mechanical properties of indi- 4. Zhang, Y. & Huang, H. Do Twin Boundaries Always vidual NWs are investigated using tensile, bending and Strengthen Metal Nanowires? Nanoscale Res. Lett. indentation experiments. The tensile experiments re- 4, 34–38 (2009). vealed increased yield strength in comparison to the bulk. The plastic deformation behavior in indentation tests is highly orientation dependent due to the twin boundaries. The interaction differences between the 218 Talks Topic E 8: Size effects and small-scale mechanical behavior of materials Influence of artificial defects on the mechanical behavior of Au nanowires Charlotte Ensslen1, Christian Brandl1, Gunther Richter2, Oliver Kraft1 1Karlsruhe Institute of Technology, Germany 2Max Planck Institute for Intelligent Systems, Stuttgart, Germany Nanostructured materials are of interest for both fun- The deformation behavior and microstructural evo- damental scientific and applied research which can be lution was further investigated by post-mortem TEM ascribed to their outstanding mechanical properties, analysis. Additionally, the experimental work is sup- e.g. Au nanowires can exhibit high strength (of the or- ported by molecular dynamics (MD) simulations. der of the ideal strength) and ductility (Sedlmayr et al. The data indicate that the measured strength of the 2012). In general, it can be observed that a decrease in nanowires is not changed for pore sizes in the range of the sample dimension results in an increase in strength 25 nm and below. Plastic deformation takes place by known as mechanical size effect (see for review, e.g., the nucleation of partial dislocations and the formation Kraft et al. 2010). However, data considering the me- of nanotwins and stacking faults. The plastic deforma- chanical properties of nanostructures with dimensions tion zone extents over the whole length of the nano- smaller than 100 nm are still rare and the correspond- wire and is not localized at the nanopore. Neverthe- ing deformation mechanisms and the influence of the less, final fracture of all nanowires occurred next to the microstructure, e.g. inherent defects, on the strength nanopores. These experimental findings are consistent has not been studied comprehensively. In order to de- with the MD simulations. velop a profound understanding of the role of defects for the deformation mechanisms of single crystalline References Au nanowires, we make use of a helium ion micro- Andreas Sedlmayr, Erik Bitzek, Daniel S. Gianola, scope. It offers the possibility to modify nanostructures Gunther Richter, Reiner Mönig, Oliver Kraft (2012): by altering the surface characteristics or creating nano- Existence of two twinning-mediated plastic defor- pores in the nanowire prior to mechanical testing. mation modes in Au nanowhiskers – Acta Mater. 60: In-situ tensile tests of modified Au nanowires contain- 3985-3993. ing nanopores were performed in an SEM chamber. Oliver Kraft, Patric A. Gruber, Reiner Mönig, and Dan- The simultaneous observation of the specimens upon iel Weygand (2010): Plasticity in confined dimen- testing allows an image-based strain measurement and sions. – Annu. Rev. Mater. Res. 40: 293-317. the characterization of the fracture sites after testing. In-Situ Electromechanical Properties of ZnO Nanowires Sanjit Bhowmick, Ude Hangen, Douglas Stauffer, Syed Asif Hysitron, Inc., Minneapolis, USA One-dimensional structures such as nanowires and sweeps at constant strain were performed to obtain I-V nanotubes are potential materials for future nanoelec- curves in order to extract electrical properties. Period- tronics, optoelectronics, piezoelectric devices, sensors, ic stress or strain from the nanowires was generated and actuators. Due to length scale effects and higher by periodic variation of the applied voltage or current. surface-to-volume ratios, nanostructures can exhib- The EPTP device is a MEMS-based uniaxial nanotensile it superior mechanical and electrical, as well as other test platform that has been designed for electrome- length scale dependent properties. In this work, strain- chanical characterization of one-dimension structures. rate controlled tensile experiments were conducted on In this presentation, strain-induced electronic mobility zinc oxide nanowires using an electrical push-to-pull and piezoelectric response of ZnO will be addressed. (EPTP) device in the SEM and TEM. A source/meas- The electronic properties of such nanowires and how ure unit was used for DC current sourcing and volt- these properties can be tailored by applying strain will age measurements in four-point probe mode. Voltage also be discussed. 219 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic F 1: Advanced steels and steel composite materials 220 Talks Topic F 1: Advanced steels and steel composite materials Mechanical Properties of a 0.2%C–1.5%Si–5%Mn TRIP-aided Annealed Martensitic Steels Kohichi Sugimoto, Hikaru Tanino Shinshu University, Nagano, Japan Impact toughness of a 0.2%C–1.5%Si–(1.5–5.0)%Mn highest tensile strength and the largest total elonga- transformation-induced plasticity (TRIP)-aided steels tion by a TRIP effect of metastable retained austenite. which were subjected to intercritical annealing and However, the Charpy impact absorbed value was lower then isothermal transformation process after quench- and ductile-brittle transition temperature was higher ing was investigated for automotive applications. The than those of 1.5%Mn steel. This was caused by low- Microstructure of these steels composed of annealed er retained austenite stability and easy grain boundary martensite structure matrix and retained austenite of fracture by an addition of high Mn content, despite of 10–40 vol%. The retained austenite fraction increased a larger amount of metastable retained austenite of 40 with increasing Mn content. 5%Mn steel possessed the vol%. Nano-laminate TRIP-TWIP steel with dynamic strain parti- tioning and enhanced damage resistance C. C. Tasan, M-M. Wang, D. Ponge, D. Raabe Max-Planck-Institut für Eisenforschung GmbH, Duesseldorf, Germany Conventional martensitic steels have limited ductility The results reveal that (i) the strain partitioning be- due to insufficient microstructural strain hardening tween austenite and martensite is governed by a highly and damage resistance mechanisms. It was recently dynamical interplay of dislocation slip, deformation-in- demonstrated that the ductility and toughness of mar- duced phase transformation (i.e. causing TRIP effect) tensitic steels can be improved without sacrificing the and mechanical twinning (i.e. causing twinning-in- strength, via partial reversion of the martensite back to duced plasticity (TWIP) effect); and (ii) the nano-lam- austenite [1]. inate microstructure morphology leads to enhanced These improvements were attributed to the presence damage resistance [2]. The presence of both effects re- of transformation-induced plasticity (TRIP) effect of the sults in enhanced strain hardening capacity and dam- austenite phase, and the precipitation hardening (mar- age resistance, hence, the enhanced ductility. aging) effect in the martensitic matrix. However, a full The mechanical properties of the system is then fur- micro-mechanical understanding of this ductilizing ef- ther optimized by a cold rolling treatment which intro- fect requires a systematic investigation of the interplay duces austenitic zones of different stability, and hence, between the two phases, with regards to the underly- further enhanced strain hardening capacity. ing deformation and damage micro-mechanisms. For this purpose, in this work, a Fe-9Mn-3Ni-1.4Al- References 0.01C (mass %) medium-Mn TRIP maraging steel is [1] Wang, M-M, Tasan, C.C., Ponge, D., Kostka, A., produced and heat treated under different reversion Raabe, D., Smaller is less stable: size effects on twin- conditions to introduce well-controlled variations in ning vs. transformation of reverted austenite in TRIP the austenite-martensite nano-laminate microstruc- maraging steels, Acta Materialia, 79 (2014), 268-281. ture. Uniaxial tension and impact tests are carried out [2] Wang, M-M, Tasan, C.C., Ponge, D., Dippel, A-C., and the microstructure is characterized using scanning Raabe, D., Nano-laminate TRIP-TWIP steel with dynam- and transmission electron microscopy based tech- ic strain partitioning and enhanced damage resistance, niques and post-mortem synchrotron X-ray diffraction Acta Materialia, 85 (2015) 216-228. analysis. 221 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Characterization of strain localizations during plastic defor- mation of TRIP/TWIP steels Anja Weidner, Christian Segel, Horst Biermann TU Bergakademie Freiberg, Institut für Werkstofftechnik, Germany Modern high-alloy CrMnNi TRIP/TWIP steels exhibits microstructure (e-martensite, α’-martensite, twins either a deformation-induced martensitic phase trans- etc.). The results of the image correlations show a formation or mechanical twinning depending on the significant difference in the formation of local strain austenite stability and the stacking fault energy, which fields depending on the primary deformation mecha- are influenced both by the chemical composition as nism influenced by the chemical composition and the well as by the deformation temperature. In the past, deformation temperature. Moreover, the magnitude the individual deformation mechanisms were studied of shear for individual constituents of the microstrucu- already intensively by comprehensive microstructural tre like deformation bands with stacking faults (e-mar- investigations using electron microscopy [1] or X-ray tensite), α’-martensite or mechanical twins were cal- diffraction [2]. In addition, studies on the kinetics of culated. Forthermore, it is shown that the magnitude these deformation processes were performed apply- of shear of α’-martensite islands depends significantly ing acoustic emission measurements [3]. Although, the on their crystallographic orientation [4]. mechanisms of the formation of α’-martensite as well as the variant selection of α’-martensite were investi- References gated by numerous authors even by molecular dynam- Biermann, H., Solarek, J. Weidner, A. (2012): SEM In- ics simulations and the magnitude of shear for e-mar- vestigation of high-alloyed austenitic stainless cast tensite/stacking faults and twins are known from theo- steels with varying austenite stability at room tem- retical considerations. Up to now the experimental de- perature and 100°C, Steel research international 83 termination of the individual local shear strain values (6) 512-520. associated with different mechanisms like α’-nuclei or Rafaja, D., Krbetschek, C., Ullrich, C., Martin, S. (2014): mechanical twins is still missing. An excellent method Stacking fault energy in austenitic steels determined for the experimental determination of these individual by using in situ X-ray diffraction during bending, J. strain levels is the performance of quasi in situ defor- Appl. Cryst. 47 936-947. mation experiments in a scanning electron microscope Vinogradov, A., Lazarev, A., Linderov, M., Weidner, complemented by the application of the digital image A., Biermann, H. (2013): Kinetics of deformation correlation (DIC) technique on high-resolution SEM im- processes in high-alloyed cast transformation-in- ages of etched specimen surfaces giving perfect con- duced plasticity/twinning induced plasticity steels trast conditions for an excellent pattern recognition. determined by acoustic emission and scanning Tensile deformation experiments were performed at electron microscopy: Influence of austenite stability room and elevated temperature using a push-pull load- on deformation mechanisms, Acta Mater. 61 2434- ing stage inside a field-emission SEM. The DIC-tech- 2449. nique was used to evaluate local strain fields in the Weidner, A., Segel, C., Biermann, H. (2015): Magni- microstructure developping in dependence on the ap- tude of shear of deformation-induced α’-martensite plied global strain. The areas of interest were analyzed in high-alloy metastable steel, Mater. Lett., accept- after the tensile tests by electron backscattered-dif- ed. fraction (EBSD) in order to characterize the developed Temperature evolution during tensile straining of high Mn twinning induced plasticity (TWIP) steels JeeHyun Kang, Tobias Ingendahl, Wolfgang Bleck Steel Institute, RWTH Aachen University, Germany It is well known that the mechanical properties of high and determines the predominant deformation mecha- Mn austenitic steels are influenced by their stacking nisms such as TWinning Induced Plasticity (TWIP) and fault energy (SFE) which depends on the temperature TRansformation Induced Plasticity (TRIP) (Saeed-Ak- as well as composition (Saeed-Akbari 2009 and 2012), bari 2012). During the deformation of a metal, 70-95% 222 Talks Topic F 1: Advanced steels and steel composite materials of mechanical energy is disspated as heat and the tem- Fe18Cr10Ni0.05C steel, such temperature change is perature increases accordingly (Zehnder 1990). Espe- smaller in high Mn steels, possibly due to its higher cially for high Mn austenitic steels where inhomoge- heat capacity. The corresponding SFE change of the neous deformation occurs at room temperature (Chen high Mn steels depends on the composition. The global 2009), it is likely that the generated heat accumulates and local temperature rise would result in a SFE change in a local region. It is expected that such temperature of only 1 mJm-2 and 2 mJm-2, respectively, which is too rise would influence SFE and may affect the deforma- small to influence the deformation mechanism. tion behaviour. In conclusion, temperature rises up to ~40-45ºC during In this study, three high Mn austenitic TWIP steels the tensile deformation of high Mn steels. The temper- (Fe29Mn0.4C, Fe22Mn0.5C, Fe24Mn0.7C, numbers in ature increase does not depend on the high Mn steel wt%) are uniaxially deformed by employing quasistatic composition, while that of a Fe18Cr10Ni0.05C steel is tensile tests with infrared thermography at room tem- higher, reaching up to ~65ºC due to necking. When in- perature. When inhomogeneous deformation takes homogeneous deformation occurs in high Mn steels, place, both global and local temperature evolutions local temperature can reach up to 55ºC. However, such are acquired and plotted with respect to the applied increase results in 1-2 mJm-2 increase in stacking fault mechanical energy. The temperature evolution is com- energy, which is unlikely to affect the deformation pared with a Fe18Cr10Ni0.05C austenitic stainless mechanism. steel, which shows homogeneous deformation behav- iour. Finally, their SFEs were estimated according to the References observed temperature change. Saeed-Akbari, A. & Mosecker, L. & Bleck, W. (2012): The invetigated high Mn steels show different strength Characterization and prediction of flow behaviour in and ductility as well as the onset point of the inho- high-manganese twinning induced plasticity steels: mogeneous flow. During elastic deformation, a small part I. mechanism maps and work-hardening behav- decrease in temperature (~0.1-0.2ºC) is observed due ior – In: Metall. Meter. Trans. A, 43A: 1688-1704. to thermoelastic coupling. The decrement is inverse- Saeed-Akbari, A. & Imlau, U. & Bleck, W. (2009): ly related to heat capacity of the steels. During plastic Derivation and variation in composition-dependent deformation, the global temperature is described as a stacking fault energy maps based on subregular function of the mechanical energy and does not de- solution model in high-Mn steels – In: Metall. Me- pend on the composition among the high Mn steels. ter. Trans. A, 40A: 3076-3090. It gradually increases to ~40-45ºC during deformation. Zehnder, A.T. (1991): A model for the heating due to Once inhomogeneous deformation takes place, it is plastic work– In: Mech. Res. Comm. 16, 23-28. clearly detected in temperature profiles. The differ- Chen, L. & Kim, H.-S. & Kim, S.-K. & De Cooman B.C. ence between local and global temperatures increas- (2009): Localized deformation due to Portevin-Le- es with the mechanical energy up to ~10ºC and does Chatelier effect in 18Mn-0.6C TWIP austenitic steel not depend on the composition. Comparing it with a – In: ISIJ Inter., 47:1804-1812. Microstructure as well as mechanical and magnetic proper- ties of Fe-based alloys with different contents of metastable austenite Marek Smaga, Dietmar Eifler, Tilmann Beck Institut of Materials Science and Engineering, University Kaiserslautern, Germany Metastable austenitic microstructures can be achieved The initial microstructure after heat treatment is main- in steels due to alloying elements like Cr, Ni, Mn, Si and ly a ferritic-bainitic matrix with dispersed retained Al. Dependent on the amount of these elements and metastable austenite islands. The fully austenitic TRIP/ special heat treatments, advanced steels with a low TWIP steels are produced generally based on two alloy- content of retained metastable austenite (< 15 vol.-%) ing concepts: 1st: Cr-Ni-concept for corrosion resistant - so called low alloyed TRIP steels, or fully austenitic stainless steels (18 % Cr / 10 % Ni) and 2nd: Mn-Si-Al- steels - so called high alloyed TRIP/TWIP steels can be concept for new, advanced austenitic steels, where produced. Some low alloyed TRIP steels were included a large variance in chemical composition exists and in the new German/European standard DIN-EN 10346. sometimes an addition of Cr and Ni is used. Depending 223 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 on the chemical composition and consequently varying stacking fault energy in the metastable fully austenitic steels the TWIP-effect occurs along or instead of the TRIP-effect. In this contribution the microstructure as well as mechanical and magnetic properties of three types of metastable austenitic steels: (1) low alloyed, (2) Cr-Ni and (3) Mn-Al-Si are presented and discussed. The monotonic deformation behavior and magnetic properties of all investigated materials were charac- terized by stress-strain-measurements as well as in si- tu-measurements of magnetic data using a Feritscope® and Hall-Probe during tensile tests. Additionally stress controlled fatigue tests specimens with measurements Fig. 1: Development of ferromagnetic of stress and magnetic data were performed on Cr-Ni α´-martensite content and change in the magnetic steel. The monotonic and cyclic plastic deformation induction during random loading of AISI 321. of metastable austenite leads to a phase transforma- tion from paramagnetic austenite into ferromagnetic After comprehensive analyses of the magnetic data, α´-martensite. Furthermore, according to the Villari a constant ratio between standard deviation (xσ) and effect (Villari 1865) the change in the magnetic induc- mean value (ξM) of measured Feritscope® data (ξ) was tion due to deformation of ferromagnetic phases was observed. This ratio directly correlates with fatigue and measured. Both results, the martensite fraction and increases with a decrease of fatigue life. By this means the change in the magnetic induction can be used for magnetic properties offer a possibility for the charac- the estimation of the actual fatigue state using magnet- terization of microstructure, stress-strain-state and fa- ic measurements (Smaga, M., Eifler, D. 2009). Figure tigue in advanced metastable austenitic steels. 1 shows the change in the magnetic induction during random fatigue loading of AISI 321 with a maximum References stress of 450 MPa at ambient temperature. It can be Villari, E. (1865): Ueber die Aenderungen des magnet- clearly seen, that besides an increase of mean value ischen Moments, Bericht d. Berliner Akad., 87-122. (blue points), which correlates with the ferromagnetic Smaga, M., Eifler, D. (2009): Fatigue life calculation of α´-martensite, a change in the magnetic induction at metastable austenitc steels on the basis of magnetic each load time can be detected (lines). measurements, MP Materials Testing, vol. 51, pp 370-375. Microstructural Evolution of TRIP-aided Medium Mn Steel During Warm Deformation Yongmoon Lee1, Chong Soo Lee1,2 1 Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Republic of Korea 2 Department of Materials Science and Engineering, Pohang University of Science and Technology, Republic of Korea Medium Mn steels, classified as one of third genera- sulting microstructures were investigated paying at- tion advanced high strength steels, are widely studied tention to two phenomena (dynamic strain-induced for its reasonable combination of strength and duc- transformation and dynamic recrystallization), which tility. To enhance the mechanical properties further, varied with temperature. Variation of texture and crys- many investigations have attempted to achieve grain tallographic orientation relationship were analyzed by refinement in various ways. The aim of this work was use of electron backscatter diffraction. Finally, a new to establish more efficient process for grain refinement process for fabricating ultrafine-grained alloy by warm of medium Mn steels. Uniaxial compression tests were deformation was suggested. carried out in the temperature range of 773-973K. Re- 224 Talks Topic F 2: Advanced steels and steel composite materials Talks Topic F 2: Advanced steels and steel composite materials 225 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Influence of temperature on fatigue-induced martensitic phase transformation in a metastable CrMnNi-steel Horst Biermann, Matthias Droste, Alexander Glage Technical University Bergakademie Freiberg, Institute of Materials Engineering, Germany An interesting field for current research are metastable (EBSD) to study the temperature-dependent deforma- austenitic steels showing the TRIP (transformation in- tion mechanisms and phase transformations. Subsidi- duced plasticity) effect based on deformation-induced ary to these findings this study deals with the accord- martensitic transformation. This results in higher ant cyclic deformation curves as well as fatigue lifetime strength and superior ductility at the same time. Be- estimation using the plastic stress-strain product SSPpl sides monotonic loading martensitic transformation (Glage 2014). can be observed during cycling loading as well. In this The study shows that decreasing temperatures as well regard, it is generally agreed that a certain strain am- as increasing strain amplitudes result in a shift of the plitude and a threshold of the cumulated plastic strain onset of the martensitic transformation to a lower have to be exceeded to trigger the martensitic trans- threshold of the cumulated plastic strain, and the max- formation. imum transformed amount of α´-martensite increases. Two of the major variables for the deformation-in- Thus, the Md,c-temperature increases with increasing duced martensitic transformation are the austenite total strain amplitudes and finally is approaching a stability and the stacking fault energy (SFE) which both maximum value. depend on the temperature. As the temperature rises, Furthermore increasing temperatures lead to a fa- the austenite stability and the SFE increase, leading to tigue-lifetime improvement at high strain amplitudes, a suppression of the martensite transformation and whereas decreasing temperatures result in a fatigue a fluent transition to other deformation mechanisms lifetime enhancement at low strain amplitudes which like twinning and finally dislocation glide (Martin et could be explained with different operating deforma- al. 2011). Accordingly, in case of monotonic loading tion mechanisms. Nevertheless, the SSPpl is able to there is the so called Md-temperature representing the give a reliable fatigue lifetime estimation for the whole highest temperature at which martensitic transforma- range of temperatures. tion can take place. Analogue, this study presents a Md,c-temperature for cyclic loading as a function of the References total strain amplitude for the investigated high-alloy Glage, A. (2014): Zyklisches Verformungsverhalten CrMnNi steel (16.3Cr-7.2Mn-6.6Ni-0.03C-0.09N-1.0Si). von partikelverstärkten Verbundwerkstoffen mit For this purpose, total strain controlled fatigue tests metastabiler austenitischer Matrix – Doctoral thesis, were performed at temperatures ranging from 10°C Freiberg. to 200°C. The α´-martensite fraction was determined Martin S. et al. (2011): Influence of temperature on in situ by a feritscope. Furthermore, the post mortem phase transformation and deformation mechanisms microstructure was examined using back-scattered of cast CrMnNi-TRIP/TWIP steel – In: Solid State electron contrast (BSE), electron channelling contrast Phenomena, Vols. 172-174, pp. 172-177. imaging (ECCI) and electron backscatter diffraction Importance of ε-martensite on embrittlement and fatigue crack growth in Fe-Mn-based austenitic steels Motomichi Koyama1, Huichao Li1, Takahiro Sawaguchi2, Kaneaki Tsuzaki1, Hiroshi Noguchi1 1 Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, Fukuoka, Japan 2 National Institute for Materials Science, Ibaraki, Japan High Mn austenitic steels with low stacking fault en- The former one, deformation twinning, enhances work ergy have been known to show deformation twinning hardening capacity, improving a balance of strength and ε-martensitic transformation. Since these charac- and ductility owing to twinning-induced plasticity teristic deformation modes have possitive influences (TWIP) effect. On the other hand, the latter one, ε-mar- on mechanical properties, threse steels are expeted to tensitic transformation, has both negative and positive be use for practical automobile and damping materials. effects on mechanical damage evolution. 226 Talks Topic F 2: Advanced steels and steel composite materials As the negative effect, ε-martensitic transformation with ε-martensitic transformation in Fe-Mn-C and Fe- causes embrittlement associated with γ/ε interface Mn-Si-Al austenitic steels. More specifically, we focus or intersections of ε-martensite and annealing twin on two points: 1) ε-martensiote/annealing twin bound- boundaries. Since even TWIP stees show ε-martensit- ary intersection cracking in a tensile deformation and ic transformation at a slightly lower temperature than 2) imporatnce of fatigue crack-propagation-induced room temperature, understanding ε-martensite-relat- ε-martensite in a strain-controlled low cycle fatigue, ed embritlement mechanism in Fe-Mn austentiic steels which were clarified by EBSD/ECCI microstructure ob- is crucially important to practically use Fe-Mn austenit- servations and plastic replica method. ic steels. As the possitive effect, fatigue crack growth in a References strain-controlled low cycle fatigue testing was clarified M. Koyama, T. Sawaguchi and K. Tsuzaki: ISIJ Int. 52 to be deaccelerated by ε-martensitic transformation (2012), 161. via deformation-induced reversible transformation, M. Koyama, T. Sawaguchi and K. Tsuzaki: Metall. Trans. providing a new material design strategy to break Man- A 43A (2012), 4063. son-Coffin’s law. T. Sawaguchi, L.G. Bujoreanu, T. Kikuchi, K. Ogawa, M. In this report, we show some important aspects on em- Koyama and M. Murakami: Scripta Mater. 59 (2008), brittlement and fatigue damage evolution associated 826. Importance of strain aging on fatigue limit in austenitic TWIP steels Yuusuke Yamamura1, Motomichi Koyama1, Renqing Che1, Takahiro Sawaguchi2, Kaneaki Tsuzaki1, Hiroshi Noguchi1 1 Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, Fukuoka, Japan 2 National Institute for Materials Science, Ibaraki, Japan Strain aging is an important factor enhancing fatigue In this study, rotary bending testing was conducted at a strength. Fatigue limit of steels are determined by crit- frequency of 30 Hz and room temperature. The fatigue ical conditions associated with two cracking behavior crack growth behavior was observed by replica tech- critical stresses for crack initiation and propagation. nique and optical microscopy. The latter one is so called non-propagation fatigue Now, it was confirmed that fatigue crack stopped in a crack. The non-propagating fatigue crack phenome- stress amplitude of about 350MPa in the TWIP steel non is dominated by strain aging of carbon in steels. including carbon in smooth specimens. In contrast, the In case of major steels, carbon brings about dynamic fatigue crack in the carbon-free TWIP steel does not strain aging, preventing fatigue crack growth. However, stop in a stress amplitude of about 180MPa in smooth non-propagating fatigue crack phenomenon in auste- specimens. Namely, as we expected, strain aging was nitic steels has not clarified yet, and is expected to be elucidated to enhance non-propagating crack phenom- observed when strain aging occurs also in austenite. enon even in austenitic TWIP steels. In recent years, twinning-induced plasticity (TWIP) Additionally, in this article, we introduced a notch steels have been drawn attention as automobile ma- which is regarded as pre-crack through a combined use terials because the steels show an exceptional balance of Focusing Ion Beam (FIB) and micro hole drilling to of strength and ductility. Here note that there are two investigate short fatigue crack propagation properties typical types of TWIP steel: carbon-added and car- more clearly. The sharp notch consists of a drill hole bon-free TWIP steels. The carbon-added TWIP steels with dimensions of 100μm in diameter and 100μm in are known to show dynamic strain aging, while the car- depth, and two FIB-notch with dimensions of 50μm in bon-free TWIP steels do not. Because of the strain ag- length, 6μm in width, and 33μm in depth. This notch ing effect, the two types of TWIP steels are speculated is placed on the specimen surface and along the trans- to show a clear difference in fatigue limit. Therefore, verse direction against the loading direction. In this we studied influences of dynamic strain aging on fa- report, we will discuss the results obtained in the FIB- tigue properties through a comparative study between notched specimen as well as those in smooth speci- the austenitic TWIP steels. mens. 227 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Influence of Si addition on deformation and fracture behav- iors of aging treated cast Fe-Mn-Al-C lightweight steel Soon Il Kwon1, Je Hyun Lee1, Seong Jun Park2, H yun Uk Hong 1* 1Departement of Materials Science and Engineering, Changwon National University, Gyeongnam, Korea 2Ferrous Alloy Department, Korea Institute of Materials Science, Gyeongnam, Korea Considering environmental, economical require-ments First, 550 and 530˚C aging treatments have been taken and outstanding mobility is becoming more important to determine peak aging condition. After 550˚C aging in these days when we design and develop reduction response, the peak aging hardness(407Hv) of 1%Si weight steels that are tageting at the army vehicles ap- specimen is higher than that of no Si specimen(369Hv) plication. Thus, there are many studies to investigate and 530˚C peak aging hardness is 430Hv and 385Hv for the high specific steels that use the aging hardenable 1%Si specimen and no Si specimen, respectively. How- Fe-Mn-Al-C system. These steels are almost 15% less ever, 530˚C peak aging condition required too much dense than traditional steels and are completely auste- longer time than 550˚C aging treatment. It should be nitic when solution treated above 950˚C. The concept noted that age hardening kinetics is similar regardless of the lightweight steel is high amount of Mn and Al of 1%Si sddition. And then, 550˚C peak aged 1%Si spec- contents(respectively about 30% and 10% contents) imen showing tensile strength up to 1000 MPa with an [1]. High Mn contents led to fully austenitic matrix. excellent 26.3% elongation could be obtained at room In addition, high Al contents could be lighter weight temperature. One interesting point is that 1%Si spec- than the other conventional steels about 15% and it imen has better strength properties than no Si spec- caused κ-carbide precipitation with a chemical for- imen. After tensile test, fracutred surface and tensile mula (Fe,Mn)3AlC in the austenitic matrix by spinodal deformation were observed by SEM and TEM analysis. decomposition during aging treatment. κ-carbide is a 1%Si specimen was observed to have cleavage frac- f.c.c.-based phase of L’12 ordered crystal sturctures, tures on fractured surface in some area unlikely no Si which resemble that of perovskite oxide[2]. The or- specimen. In addition, persistent slip band was clearly dered L’12 structure which is similar to that of L12 in revealed under fractured surface. The investigation of Ni-base superalloy. Hence, lightweight steel has strong the relationship between Si addition and tensile defor- precipitation hardening effect by κ-carbide precipita- mation was discussed in this paper. tion. It means that studying about aging response in focused κ-carbide precipitation is essential to under- References stand mechanical properties in this steel. Furthermore, [1] R. Howell, L. Bartlett, A. Schulte, D. Van Aken and adding Si contents was known to prevent precipitation K. Peaslee. A Review of the Physical and Mechanical of harmful phases like β-Mn at grain boundaries. And Properties of a Cast Hight strength and Lightweight It is determined that silicon additions lowered liquidus Fe-Mn-Al-C Steel. MS&T, 2010, October, 17-21. dendrite coherency point(DCP), and solidus tempera- [2] W. K. CHOO, J. H. KIM and J. C. YOON. Microstruc- tures by approcimately 30˚C[3]. However, the effect of tural change in austenitic Fe-30.0wt%Mn-7.8wt%Al- Si upon the mechanical behaviors has not been suffi- 1.3wt%C initiated by spinodal decomposition and ciently reported. It means that there are not enough its influence on mechanical properties. Acta mater, reference for relationship of κ-carbide precipitation 1997, No 12, 45, 4877-4885. with Si addition. Especially, the investigation of defor- [3] R. Howell, S. N. Lekakh, D.C. Van Aken and V.L. mation mechanism and dislocation behaviors is needed Richards. The effect of silicon content on the fluidity to understand Si addition effect. Therefore, the of aged and microstructure of Fe-Mn-Al-C alloys. Transac- cast Fe-Mn-Al-C lightweight steel has been investigat- tions of the American Foundry Society, 2008. ed with or without 1%Si addition in the present study. 228 Talks Topic F 2: Advanced steels and steel composite materials Effect of shot peening on microstructure of steels exhibiting a TRIP effect – Experimental and modeling approaches Romain Guiheux1,2,3, Sophie Berveiller2, Denis Bouscaud2, Régis Kubler3, Etienne Patoor2, Quentin Puydt1 1IRT M2P, Metz, France 2LEM3, Arts et Métiers ParisTech, Metz, France 3MSMP, Arts et Métiers ParisTech, Aix-en-Provence, France Shot peening process is commonly used in mechanical formed on 60*60*8 mm3 samples using cut wire steel industries to increase life duration of mechanical and shots (700HV); the turbine rotational speed was varied structural parts, as automotive gears for instance. It between 500 and 2000 rpm. An augmentation of this is based on the development of residual compressive speed increased the maximum residual stress in both stresses at the surface of the component as the sur- phases. Moreover, the higher the turbine rate was, the face is hardened by the impact of steel shot. The stress higher the martensite volume fraction and the affected magnitude and the affected depth depend on the pro- depth were. cess parameters, such as the shot velocity and diame- In parallel, finite element simulations of shot peen- ter, their incidence angle with respect to the surface, ing are performed taking into account residual stress- the coverage… In the case of TRIP-effect steels, the es, plastic strains and hardening parameters for each metastable austenite can transform into martensite phase. It is based on the shot peening model with during shot peening. The final stress state is then more stress and microstructure gradients developed previ- complex as it results from mechanical strain imposed ously by Renaud (Renaud 2011); a semi-phenomeno- by the process and the martensitic transformation that logical transformation behaviour law for unstable aus- leads to stress redistribution between austenite and tenite (Kubler 2011) has been implemented to consid- martensite. The aim of this work is to study the behav- er microstructure phase evolution. Model parameters iour of TRIP-effect steels submitted to shot peening by are calibrated from tensile tests and from single-shot taking into account martensitic transformation. impact experiments on AISI 301LN. Output data are There are several existing models of shot peening giving the martensite volume fraction, the residual stress and the resulting stress field in the material as a function of strain fields in each phase, as a function of the depth parameters process; however, to our knowledge, none from the surface. Numerical results are compared to of these integrates the phase transformation. There- experimental ones on shot peened surfaces. fore we have performed experimental characteriza- tions and developed a specific model for shot peening References using a AISI 301LN stainless austenitic steel. Renaud P. (2011) : PhD Thesis - Arts et Métiers Paris- Residual stresses are determined by X-ray diffraction in Tech ; Aix en Provence, France. both phases, austenite (with Mn radiation) and mar- Kubler R., Berveiller M., Buessler P. (2011): Semi phe- tensite (with Cr radiation), using the classical sin2ψ law. nomenological modelling of the behavior of TRIP The martensite volume fraction is also measured by steels. International Journal of Plasticity, 27, 299- X-ray diffraction taking into account crystallographic 327. textures. The mechanical behavior was characterized by tensile tests at different strain rates. Shot peening was per- 229 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Study of Lüders band propagation using IR thermography and DIC method in the wide range of strain rates Michal Maj Institute of Fundamental Technological Research, Polish Academy of Sciences, Warsaw, Poland The present paper is devoted to the experimental observed. For higher strain rates the additional differ- analysis of the Lüders band propagation in C45 steel ently oriented narrow bands are present. Presence of during uniaxial tension using infrared thermography such bands at high strain rates can be a result of neces- (IRT) and digital image correlation (DIC) method. The sity of accommodation of internal stresses generated analysis was performed in wide range of strain rates due to mounting of the specimen in grips of testing (10-3 s-1 ÷ 101 s-1 ). Used high speed IR camera gives machine. At lower deformation rates such accommo- possibility of studying the thermal effects accompa- dation is probably possible within the band by an evo- nying Lüders band propagation close to the adiabatic lution of dislocation structure. conditions when the heat transfer within the specimen It has been shown that the dependence between and between specimen and the surroundings can be displacement rate and the Lüders front speed calcu- neglected (Maj 2012). Use of such equipment allowed lated on the basis of thermal images is not linear un- us to study not only the speed of front propagation but like the results known from the literature (Louche & also the initiation and morphology of the front. It has Chrysochoos 2001). Observed non-linear dependence been shown that both the front speed and the band between front speed and displacement rate may indi- morphology evolve with changing the displacement cate that there can be the limit value of front speed for rate. higher deformation rates. It was found that the Lüders plateau is observed at The results obtained using IRT technique will be ver- all considered displacement rates. Nevertheless, the ified using analysis of coupled displacement field ob- significant force fluctuations are observed above the tained using DIC method. strain rate equal to 1⋅100 s-1 . The increase in displace- ment rate results in both the lengthening of Lüders pla- References teau and the increasing level of external force. In other Maj, M. (2012): Analysis of plastic strain localization words, after the band passage the higher elongation on the basis of strain and temperature fields. – and hardening of the specimen are observed. Arch. Metall. Mater., 57(4): 1111-1116. The analysis of thermal images has shown that due to Louche, H. & Chrysochoos, A. (2001): Thermal and increase of the displacement rate not only the front dissipative effects accompanying Lüders band prop- speed but also the band morphology are changed. Up agation. – Mater. Sci. Eng., A307: 15-22. to strain rate 5 ⋅10-1 s-1 the stable front propagation is 230 Talks Topic F 3: Advanced steels and steel composite materials Talks Topic F 3: Advanced steels and steel composite materials 231 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Homogenization of TRIP steel behaviour using a strain gradi- ent plasticity model M.K. Hatami1, T. Pardoen2, P. Berke1, P.J. Jacques2, T.J. Massart1 1Université Libre de Bruxelles (U.L.B.), Belgium 2Université catholique de Louvain, Louvain-la-Neuve, Belgium An averaging procedure is developed for the simula- factors associated to each cell. Such averaging method tion of the mechanical behaviour of TRIP steels. was originally proposed in (Ognedal, et al 2014). This work further extends previous efforts to mod- The averaged response obtained is subsequently fitted el the macroscopic material behavior of TRIP steels to allow comparison with experimental stress strain which have been based, among others, on the use curves corresponding to a certain grade of TRIP steel of mean-field Mori-Tanaka approaches (Delannay, et with an experimentally obtained transformation kinet- al 2008). Comparison of their results to experiments ics, in terms of strain hardening evolution and necking motivated the introduction of size effects by means considere criterion. of strain gradient plasticity (Mazzoni, et al 2008). This The level of strain at which transformation initiates in contribution, based on a simplified representation of a each cell and the corresponding value of the associat- periodic microstructure, focused on the investigation ed weighting factor are adjusted to match the different of the effect of size dependent behaviour and higher transformation rate evolution extracted from experi- order boundary conditions combined with the local mental data available in (Delannay, et al 2008) already parameters of the transformation such as the fraction mentioned. of transforming austenite, the transformation strain, Results show that based on calibrating the strain gra- or the strain at which transformation occurs. Due to dient plasticity behaviour for the internal length scale the associated computational effort, such models were value, the homogenized response allows to successful- however restricted to the analysis of the local effects ly reproducing the evolution of the stress-strain behav- whithin a single RVE, interpreting a single transforming iour and of the strain at necking as a function of the austenite inclusion . transformation rate at various temperatures. In order to bridging the gap towards macroscopic be- The model subsequently can be used to conduct par- haviour, allowing direct comparisons with experiments, ametric studies to identify optimal transformation homogenizing this strain gradient plasticity description evolutions and to analyse how the ductility varies with is proposed. The model, in which the local transforma- local material properties. tion size effect is presented (Mazzoni, et al 2008), is replicated in a high number of different unit cells, each References of them being attributed a different strain at which the Delannay, L. & Jacques, P. & Pardoen, T. (2008): Int. J. transformation initiates, based on experimental data. Solids and Structures, 45: 1825-43. The response of each unit cell is evaluated by homoge- Mazzoni-Leduc, L. & Pardoen, T. & Massart, T.J. (2008): nizing the results of strain gradient plasticity simulation Int. J. Solids and Structures 45: 5397-418. on all these cells. Ognedal, A.S. & Clausen, A.H. & Berstad, T. & Seelig, T. The global behavior of a corresponding TRIP steel is & Hopperstad, O.S. (2014): Int. J. Solids and Struc- subsequently obtained by recombining the unit cell re- tures, 51: 1494-506. sponses by an averaging scheme based on weighting A crystal plasticity model for advanced high strength steels including both TRIP and TWIP effect Franz Roters, Su Leen Wong MPI für Eisenforschung, Düsseldorf, Germany Advanced high strength steels, such as high manga- reasons these materials are not yet widely used in in- nese steels, show an extraordinary combination of dustry. One of the reasons is a lack of suitable material strength and ductility. While this provides a tremen- models. Besides the conventional deformation by slip dous potential for many applications due to a number these materials activate additional deformation mech- 232 Talks Topic F 3: Advanced steels and steel composite materials anisms, namely twinning (Twinning Induced Plasticity, fault energy) and loading conditions (strain rate, tem- TWIP) and phase transformation (Transformation In- perature) both mechanisms can be triggered and one duced Plasticity, TRIP). This is the reason why conven- material and can even be active at the same time, it tional models used for the simulation of steels cannot is of great importance that both effects are taken into fully describe the mechanical behavior of this material account in the constitutive description. The combined class. As simulation is, however, nowadays an integral model allows us to systematically study under which part of component layout e.g. in automotive industry, conditions either one or both mechanisms together without suitable material models new materials will can be triggered during deformation. not be introduced into the production process. In our contribution we, therefore, present a crystal Reference plasticity formulation that includes both twinning and D. R. Steinmetz, T. Jäpel, B. Wietbrock, P. Eisenlohr, transformation as additional deformation mechanisms I. Gutierrez-Urrutia, A. Saeed-Akbari, T. Hickel, F. besides the conventional dislocation slip. The twinning Roters, D. Raabe (2013): Revealing the strain-hard- model is a crystal plasticity adaption of an analytical ening behavior of twinning-induced plasticity steels: model by Steinmetz et al. (2013). The TRIP model con- Theory, simulations, experiments, Acta Materialia siders both stress and strain induced transformation. 61: 494 - 510 As depending on material parameters (e.g. stacking Multiscale Modelling of Damage and Fracture in High Mn TWIP Steels Manjunatha Madivala1, Christian Segel2, Anja Weidner2, Horst Biermann2, Wolfgang Bleck1, Ulrich Prahl1 1Steel Institute, RWTH Aachen University, Germany 2Institute for Materials Technology, Technical University Bergakademie Freiberg, Germany The automobile industry has an increasing demand and to reflect void nucleation and growth of the highly for lightweight components, improved product per- deformed regions. From the analysis of the numerical formance, efficiency and increased safety. High man- tensile test, the damage initiation and flow behaviour ganese TWIP steels have superior mechanical prop- can be well predicted. erties and excellent strength to weight ratio, making Thus in this current work, to predict the material be- them ideal for the development of lightweight vehi- haviour an evaluation chain including material charac- cles. Achieved high strength and ductility rely on the terization, numerical simulation with a crystal plasticty optimization of the stacking fault energy, which gov- based material model for TWIP steels and verification erns mechanical twinning as the primary deformation by In-situ tensile tests was established. Digital Image mechanism in addition to dislocation glide and TRIP. Correlation (DIC) technique was used to identify the Numerical prediction of damage in Advanced High local failure strains. Strength Steel (AHSS) sheets is of great interest, as it is an effective way to optimize the design of parts and to References reduce the product development cycle time. F. Roters, Advanced material models for the crystal In order to predict the damage and fracture mecha- plasticity finite element method - development of nisms in TWIP steels subjected to uniaxial loading, a a general CPFEM framework, Habilitationsschrift Representative Volume Element (RVE) approach is RWTH Aachen (2011), Fakultät für Georessourcen applied to create the virtual polycrystalline micro- und Materialtechnik, RWTH Aachen University structure taking into account, the aspects of real mi- R. Quey, P.R. Dawson and F. Barbe, Large-scale 3D crostructure such as grain size, phases, grain size distri- random polycrystals for the finite element method: bution and grain orientations. The uniaxial tensile test Generation, meshing and remeshing, Computer is simulated by applying periodic boundary conditions Methods in Applied Mechanics and Engineering, and tensile load to an RVE. Crystal Plasticity (CP) based vol. 200, pp. 1729-1745, 2011 model is used for predicting the plastic localization in F. Roters, P. Eisenlohr, T.R. Bieler, D. Raabe, Crystal a material. A CZ damage model is also implemented Plasticity Finite Element Methods in Materials Sci- to predict the sudden drop of load carrying capacity ence and Engineering, Wiley-VCH, 2010 233 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Artificial microstructure model and its applications on plas- ticity and damage of the dual phase steels Napat Vajragupta, Mohamed Sharaf, Junhe Lian, Sebastian Münstermann, Wolfgang Bleck Department of ferrous metallurgy, RWTH Aachen University, Germany Heterogeneous alloy systems that contain multiple With the generated artificial microstructure model, phases possess the potential of reducing structural material’s model definition and parameters calibration component weight, energy consumption as well as are also required. For plasticity description of the con- thermo-mechanical reliability improvement. This is stituents, modified phenomenological based crystal due to the fact that the matrix of these materials con- plasticity model taking the influence of the grain size sists of constituents with strong distinction in mechan- into account is applied to ferrite and parameters are ical properties. For this reason, their industrial utiliza- calibrated by series of nanoindentation tests while tion has significantly increased in the last few decades. the empirical approach based on the measured local The application of such a material includes implemen- chemical composition is used to approximate the strain tation of the dual phase steel in the automotive indus- hardening behaviour of martensite. To characterize the try. However, the existence of these constituents in the criteria that trigger the onset of microcrack, the hybrid microstructure also results in the highly heterogene- approach combining the in-situ bending test in the ous finite stress distribution along with the high tem- large chamber SEM with the micromechanical-based perature gradients which are presented even within simulation discipline is conducted. Finally, the appli- the large components. Furthermore, the constituents cations of this introduced platform such as the strain in these material systems also affect the failure behav- hardening behaviour prediction, microcrack initiation iour in which several competing damage mechanisms simulation, shall be discussed in this study. can be observed. Therefore, a reliable microstruc- ture-based simulation approach for describing these References deformations and damage mechanisms is needed. Vajragupta, N., Wechsuwanmanee, P., Lian, J., Sharaf, Furthermore, the developed approach must be able to M., Münstermann, S., Ma, A., Hartmaier, A., & reflect the influence of microstructure morphologies Bleck, W. (2014): The modelling scheme to evaluate on the deformation behaviour of the microstructure. the influence of microstructure features on microc- Under the framework of microstructure-based simula- rack formation of DP-steel: The artificial microstruc- tion approach, the universal platform to generate the ture model and its application to predict the strain artificial microstructure model has been developed hardening behaviour – In: Computational Material and shall be discussed in this study. The ultimate goal Science, Volume 94: 198-213. for the development of this platform is to generate Okabe, A., Boots, B., Sukihara, K., & Chui S.N. (2000): the most sophisticated representative microstructure Spatial tessellation: Concepts and applications of model with as least input parameters as possible. For Voronoi diagrams, second edition: John Wiley & Son the principle of this platform, the statistical description Inc. 1992. of the necessary microstructure features such as grain Roters, F., Eisenlohr, P., Hantcherli, L., Tjahjanto, D.D., size, aspect ratio etc. is used as input parameters for Bieler, T.R., & Raabe, D. (2010): Overview of consti- the weighted Voronoi tessellation based algorithm. tutive laws, kinematics, homogenization and mul- Additionally, both 2D and 3D artificial microstructure tiscale methods in crystal plasticity finite-element model can be generated with this proposed platform modeling: Theory, experiments, applications – In: under the framework of this study. Acta Materialia, Volume 58: 1152-1211. 234 Talks Topic F 3: Advanced steels and steel composite materials Dislocation plasticity in precipitate hardened advanced aus- tenitic lightweight high-Mn steels by coupled TEM and DDD simulations: Strengthening and dislocation-based mecha- nisms E. Welsch1, S.M. Hafez Haghighat1, I. Gutierrez-Urrutia2, D. Raabe1 1Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany 2National Institute for Materials Science (NIMS), Tsukuba-city Ibaraki, Japan High performance austenitic lightweight steels with up In particular the particle size and position with respect to 15% density reduction are currently of high inter- to each other where deduced from TEM observations. est for the automotive industry. The development of In the simulation the particle size and geometry at a such weight reduced and highly formable steel grades fixed particle fraction was varied in order to elucidate for structural applications includes a range of material the role of penetrating dislocations into the channels systems. One of the most promising alloy systems are between the particles on the mechanical response. low density steels based on the FeMnAlC system [1,2]. DDD simulations in connection with TEM observa- This quaternary system offers a combination of ex- tions elucidate the character of how the geometrical cellent mechanical properties, characterized by elon- arrangement of these particles governs and influences gations of up to 70 % at stresses above 1.5 GPa, and the plastic deformation. specific weight reduction of up to 15%. Al addition pro- These investigations provide new guidelines to alloy motes the precipitation of L’12 ordered (Fe, Mn)3AlC design of advanced lightweight steels based on the un- carbides, also referred to as κ-carbides. The austenit- derlying dislocation mechanisms at different κ-carbide ic matrix of the FeMnAlC steels contains nano-sized geometrical arrangements. cuboidal κ-carbide precipitates that control the dis- location assisted plasticity of these materials. Here References we present new insights into κ-carbide strengthened [1] D. Raabe, H. Springer, I. Gutierrez-Urrutia, F. Rot- high-Mn steels by using both, transmission electron ers, M. Bausch, J. -B. Seol, M. Koyama, P. -P. Choi, K. microscopy (TEM) observations and the simulation of Tsuzaki, Alloy Design, Combinatorial Synthesis, and comparable deformed microstructures using discrete Microstructure–Property Relations for Low-Density dislocation dynamics (DDD) simulations. In the DDD Fe-Mn-Al-C Austenitic Steels, JOM, 2014, Volume simulations the model previously developed by Hafez 66, pp 1845-1856 Haghighat et al. [3] was used. Precipitates are treated [2] Springer, H., and D. Raabe, 2012, Rapid alloy proto- here as impenetrable obstacles to the motion of dis- typing: Compositional and thermo-mechanical high locations. As the model originally was developed for throughput bulk combinatorial design of structural cuboidal γ’ strengthened Ni base superalloys it had to materials based on the example of 30Mn-1.2C-xAl be modified to fulfil the requirements of the present triplex steels: Acta Materialia, v. 60, p. 4950-4959. study. [3] S.M. Hafez Haghighat, G. Eggeler, D. Raabe, Acta The κ-carbide morphology was investigated using simi- Materialia 61 (2013). lar particle arrangements as observed by TEM probing. 235 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Phase-field modeling of solid-solid phase transformations Daniel Schneider1, Oleg Tschukin2, Michael Selzer1,2, Britta Nestler1,2 KIT, Institute of Applied Materials -Computational Materials Science, Karlsruhe, Germany 2 Karlsruhe University of Applied Science, Institute of Materials and Processes, Germany Computational models based on the phase-field meth- the Gibbs-Thomson condition. Additionally we demon- od have become an indispensable tool in material sci- strate that the formulated driving force is equivalent to ence and physics in order to investigate materials with the mechanical configurational forces. complex microstructures. The models typically oper- In order to calculate the plastic strain, the Prandtl-Re- ate on a mesoscopic length scale resolving structural uss model for the particular phase is implemented changes of the material and provide valuable informa- consisting of an associated flow rule in combination tion about evolution of microstructure and microstruc- with the von Mises yield criterion and a linear isotropic ture mechanical property relations. hardening approximation (Schneider et al. 2014). Sim- For many interesting and important phenomena, such ulations are performed illustrating the evolution of the as martensitic phase transformation, mechanical con- stress and plastic strain using a radial return mapping figurational forces play an important role in the evo- algorithm for single phase system and heterogeneous lution of microstructure. In order to investigate such microstructures. phenomena a calculation of the stresses and strain Finally we show simulations in polycrystalline systems energy at the transition region is indispensable. We to martensitic phase transformation in one grain as derive a phase-field elasticity model based on force well as in multigrain systems and simulations to Green- balance and Hadamard jump condition at the inter- wood-Johnson effect. face (Schneider et al. 2015). We show the quantitative characteristics of the model, by comparing the simu- References lated stress profiles in a plate with a round inclusion Schneider et al. (2014): Small strain elasto-plastic under hydrostatic tension with the theoretical predict- multiphase-field model: Schneider, D., Schmid, S., ed stress fields and stress field calculated with Voigt/ Selzer, M., Böhlke, T., Nestler, B.: Computational Taylor and Reuss/Sachs approximation. In order to Mechanics validate the elastic contribution to the driving force of Schneider et al. (2015): Phase-field elasticity model the phase transition, we compare the resulted stress, based on mechanical jump conditions: Schneider, strain and strain energy profiles, in one dimensional D., Tschukin, O., Choudhury, A., Selzer, M., Böhlke, equilibrium condition of serial and parallel material T., Nestler, B.: submitted to Computational Mechan- chain as well as in two dimensional systems through ics 236 Talks Topic F 4: Advanced steels and steel composite materials Talks Topic F 4: Advanced steels and steel composite materials 237 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Z phase strengthened steels for ultra-supercritical power plants Daniel F. Urban, Christian Elsässer, Hermann Riedel Fraunhofer Institute for Mechanics of Material IWM, Freiburg, Germany To minimize fuel consumption and CO2 emission of fos- A possible solution to this problem is provided by the sil fired power plants, the thermal efficiency, and there- idea to exploit the Z-phase as a thermodynamically sta- fore the steam inlet temperatures, must be as high as ble strengthening agent in martensitic creep resistant possible. In the past 20-30 years sufficiently creep re- steels. Hence the challenge is to control the precipita- sistant 9% chromium steels were developed, which al- tion of the Z- phase in 12% Cr steels such that fine Z lowed to increase the steam temperature up to 615 °C. particles are formed, which are stable for long times. The increased creep resistance was mainly obtained We present atomistic simulations, using density func- by controlled precipitation of fine (V,Nb)N particles tion theory, which reveal the essential mechanisms in the steels. Further raise of the steam temperature underlying Z-phase formation. The picture that evolves calls for chromium contents higher than 9% to achieve consists of the diffusion of chromium atoms into nitride better corrosion and oxidation resistance. However, it particles and their subsequent clustering in a layered has been found that in 11-12% chromium ferritic-mar- arrangement which finally yields the transformation of tensitic steels strengthened by fine (V,Nb)N particles, the nitride particles to Z-phase particles. We study the precipitation of the thermodynamically stable Z-phase, thermodynamic stability of Z-phase and related struc- Cr(V,Nb,Ta)N, in long-time service is unavoidable and tures and predecessors as well as the basic diffusion detrimental. Usually, the Z-phase particles are coarse mechanisms. and brittle and grow at the expense of the desired fine This work is part of the Z-Ultra-Project within the EC 7th (V,Nb)N particles. framework program. Different mechanical behavior of MA957 ODS and Eurofer’97 steels exposed to flowing helium of 720˚C Anna Hojna1, Hynek Hadraba2, Jana Kalivodova1, Roman Husak2 1Centrum Vyzkumu Rez s.r.o., UJV Group, Rez, Czech Republic 2Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic Since ODS steels have been developed for the use of steels can result in the formation of coherent particles high temperature applications in the range from 400 of α’ (Cr-rich ferrite) with an increase in yield and ten- to 700˚C, thermal aging related problems at prolonged sile strength, and a reduction in ductility associated service times need to be intensively studied. The aim of with embrittlement when exposed at temperatures the work was to describe fracture behaviour of MA957 above 400˚C (Lee 2007). The degree of the embrittle- ODS steel (14%Cr, 0,3Mo, 0,9Ti, 0,25%Y2O3 produced ment, manifested in lower impact and fracture tough- by mechanical alloying process) after high temperature ness, increases with Cr content; for 14 Cr ODS it had exposure in comparison to the Eurofer’97 plate steel been indicated already at 440˚C after 320 hours of (9%Cr, 1%W) behavior. The both materials are consid- exposure. The main problems of the MA957 type ODS ered for future nuclear energy systems. are connected to lower toughness and heterogenuity Due to microstructural characteristics, the MA957 steel of behaviour as well as transition temperature behav- embodies excellent combination of high-temperature iour of ferritic matrix of the steel and strengthening strength and oxidation resistance. The fine oxide dis- by oxide dispersion. Whereas, the long-term exposure persion also serves as trapping sites for point defects of the Eurofer’97 steel at high temperatures leads to induced by radiation displacement and thus reduces different microstructural changes (Hadraba 2009); the remarkably irradiation swelling of the MA957 steel coarsening of the M23C6 (Cr rich) precipitates and (Hadraba 2011). For space nuclear reactors cooled by recrystallization of subgrains were found after ageing a gas mixture of He and Xe at reactor temperatures at 550˚C/5000 h (Stratil 2011). <1100˚C, the MA-ODS steels are particularly very at- Small specimens (MicroCharpy, 3x4x27 mm3 and mi- tractive as structure materials (El-Genk 2005). niTensile ø2 mm) were exposed to helium gas flowing in It is well known that thermal aging of high Cr ferritic the High Temperature Furnace at 720˚C for 500 hours. 238 Talks Topic F 4: Advanced steels and steel composite materials Then, the specimens were tested for the impact and References tensile behavior. The test results are compared to the Hadraba H. et al. (2011), Journal of Nuclear Materials other two sets of specimens of the previous tests, as 417, 241–244 received and isotermally annealed at 650˚C in the case El-Genk M.S. et al. (2005), Journal of Nuclear Materi- of the ODS steel. The He exposed materials showed als 340, 93–112 positive shift of transition temperature and change of Lee J.S. et al. (2007), Journal of Nuclear Materials the upper shelf value. While the upper shelf value de- 367–370, 229–233 creased in the exposed Eurofer’97, it significantly in- Hadraba H. et al. (2009), Journal of Nuclear Materials creased in the ODS steel. The difference is discussed in 386–388, 564–568 terms of microscopy observation in the paper. Stratil L. et al. (2011), Journal of Nuclear Materials 416, 311–317 Characterization of the weldability of different AHS steel and aluminium alloy grades using thermo-mechanical physical simulation János Lukács, László Kuzsella, Zsuzsanna Koncsik, Ádám Dobossy, Dóra Pósalaky Institute of Materials Science and Technology, University of Miskolc, Miskolc, Hungary The technological examinations and probes regarding The mathematical (computational) simulation may the weldability date back to the development of differ- contribute to cancelling the limitations of examina- ent welding technologies. Not only the various quali- tions and probes, as well as those of the different ap- ties of materials, but the different welding processes proaches, which are not to be considered in the current have resulted the elaboration of additional tests (Pohle study. However, the other consideration is the physical 1990). They are specified by their variety, applicabili- simulation. The basic aim of the first physical simula- ty within limits, as well as their limited comparability. tors (mid-20th century) was to provide reproducibility Considering the complex issue of weldability, such as for the welding, especially for the Heat Affected Zone materials, welding technology and welded structure (HAZ). (Easterling 1983, Boese et al. 1984), there is not one Nowadays, the physical simulation is an ultimate inno- single test which would allow evaluating the problem, vative way to develop the welding processes. The pa- it is not and would not be sensible either, consequently per introduces the connection between the weldability weldability cannot be determined with a single char- and the physical simulation, based on our investiga- acteristic. The underlying reasons are to be examined tions using Gleeble 3500 thermo-mechanical physical separately under specific conditions, which then will simulator. Four kinds of materials, two advanced high enable us to rank the different materials based on the strength steels (S690QL and S960QL) and two alumin- given results. The order of ranking depends on the re- ium alloys (5754-H22 and 6082-T6) were investigated. quirements, which means that it is not considered con- Different types of physical simulation test methods stant. The complex correlations between the factors do (Mandziej 2010) were made, such as identification of not allow defining other properties (e. g. mechanical the Nil-Strength Temperature (NST), on heating and on properties) through characteristics. Besides the exper- cooling Hot Tensile Tests (HTT), as well as HAZ-tests, to iments, tests and probes, semi-empirical and empirical characterise the weldability of the investigated materi- investigations are given an ever increasing emphasis in als. The results of the AHS steel grades and the alumin- order to avoid limitations (Buchmayr 1991). ium alloy grades were compared with each other and There is at least double contradiction in the examina- with the results can be found in the literature. tions and probes. On the one hand, the actual process- es can only be performed on small parts and in small References volumes, which means that there are only small-size Pohle, C. (1990): Zerstörende Werkstoffprüfung in der specimens available to define the data belonging to the Schweißtechnik, Deutscher Verlag für Schweißtech- materials and/or technologies (Yuan & Sharpe 1996). nik DVS-Verlag GmbH, Düsseldorf. This fact, due to the aspect of size effect, will decrease Easterling, K. E. (1983): Introduction to the Physical the reliability of the results. On the other hand, the Metallurgy of Welding, Butterworths Monographs technological investigations are reflected within limits in Materials (BMM), Butterworths & Co (Publishers) as regards the real processes. Ltd. 239 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Boese, U., Werner, D. & Wirtz, H. (1984): Das Verh- Yuan, B. & Sharpe, W. N. (1996): Fatigue testing of alten der Stähle beim Schweißen, Teil II: Anwend- microspecimens. – In: Lütjering, G. & Nowack , H. ung. Deutscher Verlag für Schweißtechnik (DVS) (eds.): Proceedings of the Sixth International Fatigue GmbH, Düsseldorf. Congress (FATIGUE’96), Pergamon, Vol. III: 1943- Buchmayr, B. (1991): Computer in der Werstoff- und 1948. Schweisstechnik: Anwendung von mathematischen Mandziej, S. T. (2010): Physical Simulation of Metallur- Modellen, Deutscher Verlag für Schweißtechnik gical Processes. – Materiali in technologije / Materi- DVS-Verlag GmbH, Düsseldorf. als and technology, 44, Issue 3: 105-119. The microstructure characterization of the HAZ and welding CCT diagram of API X100 steel Chunlin Qiu 1, Liangyun Lan 2, Xiangwei Kong 2 1 State Key of Laboratory of Rolling Technology and Automation, Northeastern University, Shenyang, China 2 School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China The growing energy demand in different areas of the time is 5s, the lath martensite volume achieved to as world and the distance between gas reservoirs and much as 50%. consumers has increased the need to transport gas Through the analysis and compare the transforma- from far away regions to the final market. The require- tion regulation both CGHAZ and FGHAZ, the started ments for pipe line steel both quality and quantity temperature of transformation has same tendency, is also increased strongly. Welding process is a very that is varied from low to high follow the decreasing important aspect because the steel pipe usually was of cooling rate, whereas the finished temperature of made by welding method. This work focus on a kind transformation varied from low to high with the de- of high strength pipeline steel (API X100) in oil and gas creasing of cooling rate when it is relatively higher, and transportation industry. then turn to decreasing follow the cooling rate decline. The chemical composition of X100 steel is(mass%): Compared with FGHAZ, the started temperature is high 0.04% C, 2.0% Mn, 0.29% Si, 0.23% Cu, 0.275%Cr, in FGHAZ, meanwhile the transformation region is en- 0.006% P, 0.0015% S, 0.55% (Ni + Nb + Mo), the bal- larged. ance is Fe. The weld cracking sensitivity index Pcm is In the low range of cooling rates, with the increasing of 0.21, the hot-rolled plate of 20mm thickness was rolled cooling rate, the microhardness values are increased into hot simulation processing sample, welding ther- in both CGHAZ and FGHAZ , but when a certain cool- mal cycle simulation test was conducted on the ther- ing rate (t8/5 cooling time is about 30s) is reached, its mal simulation machine MMS300, the different t8/5 hardness value tend to a stability and maintained at cooling time was adopted from 3 to 600s, both micro- around 325HV. structure (optical, SEM and TEM) and hardness testing were used to analyzed welding simulation samples, References then the CGHAZ-CCT and FGHAZ-CCT was plotted. Wang, P. Y., & Mou, Z. Y. (2013). Study on the Weld- The results show that for either CGHAZ or FGHAZ, the ability of X100 Pipeline Steel on Scene. Advanced granular bainite(GB) was obtained under low cooling Materials Research, 753:343-352. rate, after the t8/5 time reached 600s, MA island emerg- Amaro, R. L., Rustagi, N., Findley, K. O., Drexler, E. S., es, with characterization contained degenerate pearl- & Slifka, A. J. (2014). Modeling the fatigue crack ite. when the cooling rate reached to 10~20℃/s(t8/5 growth of X100 pipeline steel in gaseous hydrogen. is 15~30s correspondingly), Microstructure mainly International Journal of Fatigue, 59: 262-271. include ferrite and bainite which due to the Mo and Zhang, M., & Yang, L. (2013). Microstructure and Me- Nb put off the transformation form austenite to ferrite chanical Properties of Joints of X100 Line Pipe by and promote the bainite transformation. as further in- Submerged Arc Welding. Applied Mechanics and creasing of cooling rate, the volume of martensite in Materials, 310:139-144. microstructures is increasing gradually, and t8/5 cooling 240 Talks Topic F 4: Advanced steels and steel composite materials Weldability of modern high strength bainitic steel Liangyun Lan1,2, Xiangwei Kong1, Chunlin Qiu2 1School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China 2State Key of Laboratory of Rolling Technology and Automation, Northeastern University, Shenyang, China With the development of thermo-mechanically con- properties was also discussed to optimize the welding trolled process and microalloying technique, hot process. rolled steel plates always have a good balance of high The resutls showed that the strength of welded joint strength and good toughness. However, this excellent decreases with the increase in heat input and the frac- combined mechanical properties can be upset by the ture region always occurs at the weld metal, which thermal cycles experienced during welding, producing means that this is under matching welded joint. The regions of poor toughness known as local brittle zones. impact toughness of the weld metal does not change Although the weldability of modern high strength with the heat input, but the HAZ toughness gradually steels is improved through the composition design of decreases with increasing heat input. Microstructure low carbon equavilent, their welding system design observation reveals that the weld metal has prodomi- is still a difficult issue, which impedes the actual ap- nantly acicular ferrite irrespective of heat input, which plication of the new steels. As Bhadeshia (2013) said: is the main reason to keep good toughness for the weld “Super-high strength nanobainitic steel has not been metal. However, at the HAZ, the fracture mode chang- achieved commercial application mainly due to imma- es from quasi-cleavage fracture to complete cleavage ture welding system”. Therefore, to protect the welded fracture with the heat input, which is attributed to the joint from property deterioration, e.g., cleavage crack- coarse bainite formed in this region. ing, the effect of weld process on the microstructure Compared with the results proposed by Thewlis (2000), evolution should be further investigated for the mod- who also studied the weldability of X100 pipeline steel ern high strength steels. by using submerged arc welding, the minimum heat in- In this work, the submerged arc welding technique put adopted in our research can optimize the mechan- was employed to weld the high strength bainitic steel ical properties of welded joint. using various welding parameters. The main parame- ters include current, voltage and welding speed, which References determines the welding heat input from 1.4 to 4.5 Bhadeshia, H.K.D.H. (2013): The first bulk nanostruc- kJ/mm. The microstructure characteristics of welded tured metal, Science and Technology of Advanced joints was studied in detail by means of optical micro- Materials, 14: 1-8. scope, scanning electron microscope equipped with Thewlis, G. (2000): Weldability of X100 pipeline, electron backscattering diffraction technique, as well Science and Technology of Welding and Joining, 5: as transmission electron microscope. The relationship 365-377. between microstructure evolution and mechanical 241 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic G 1: Fracture mechanics 242 Talks Topic G 1: Fracture mechanics Numerical Simulation of ZrO2(Y2O3) Ceramic Plate Penetra- tion by Cylindrical Plunger Vladimir Bratov, Nikita Kazairnov, Yuri Petrov Saint Petersburg State University, Faculty of Mathematics and Mechanics, Saint Petersburg, Russia Fracture of ceramics, multi-layered ceramics and ce- penetration of ceramic plate by a cylindrical plunger. ramic composites is of a great importance in connec- The focus is primarily on energetic peculiarities of the tion with numerous theoretical and practical problems. process, including investigations of histories of fracture Theoretical problems primarily include understanding surface evolution in fractured ceramic material, calcu- the mechanisms driving static and dynamic fracture of lations of specific fracture energy at dynamic rupture this special class of materials (extremely brittle, very initiation and studies of correlation between new frac- high strength and low toughness) and elaboration of ture surface within ceramic material created as a result criteria capable of accurate prediction of fracture initi- of a plunger impact and initial plunger energy (veloc- ation, development in arrest in quasi-static and dynam- ity) as well as the properties of the ceramic material. ic conditions. While the majority of theoretical prob- Visualization and statistical analysis of target fragmen- lems connected with quasi-static ruptures of ceramic tation was used as a supplementary tool for fracture materials are solved, mechanisms underlying dynamic process investigation. fracture of these materials are not clear and general- This study is deliberately restricted to the simplest ly recognised criteria for fracture are not formed yet. possible geometry and contact problem formulation. Practical importance of these problems is evident due In the considered case, an elastic cylindrical plunger to wide usability of ceramic-based materials owing to with properties typical for steel normally hits circular unique physical and mechanical properties and the homogenous ceramic plate, behaving as linear elastic possibilities of industrial production. material up to the moment of fracture initiation. Due Dynamic fracture properties of ceramic materials are to obvious axial symmetry of the problem, two-dimen- primarily studied due to applications where ceramic/ sional problem can be formulated. Such a simplicity in multi-layered ceramics or ceramic composites serve as formulation provides a possibility to concentrate on a protection against mechanical and thermal impacts key features controlling and driving fracture of pene- on an object. Thermal effects are not considered in this trated ceramic plate. work. As regards performance of ceramic materials against high rate mechanical loads, then the function References of ceramic protection normally consists in a) absorp- Freund L.B. (1998): Dynamic Fracture Mechanics. tion of impact energy for deformation and fracture of Cambridge University Press, 584. ceramics b) redistribution of impact energy over a big- Bratov V. (2011): Incubation time fracture criterion for ger area of the surface underlying protective layer c) FEM simulations. – In: Acta Mechanica Sinica, 27(4): weight reduction of the protection system. 541-549 In this paper an approach that was previously suc- Bratov V.A., Morozov N.F., Petrov Yu.V. (2009): Dyna- cessfully applied to simulate dynamic fracture in other mic Strength of Continuum. St. Petersburg Universi- classes of quasi-brittle materials was applied to study ty Press, 224. Temporal Peculiarities of Fracture Caused by Threshold Puls- es in Spallation Grigory Volkov1,2, Yuri Petrov1,2, Yuri Mescheryakov2, Natalia Mihaylova1 1St. Petersburg State Univercity, St. Petersburg, Russia 2Institut for Problem of Mechanical Engineering RAS, St. Petersburg, Russia Spallation test is one of the basic mechanical tests for problem solution within the elastic approach shows determining the dynamic properties of materials. This that the time profile of the tensile stress pulse coin- experimental scheme allows studying the strength cides with the time profile of the free surface velocity, properties of the material under dynamic tension. Ten- which can be directly measured by laser interferome- sile stress originates in the specimen when the com- try [Zlatin et al. 1974, Bloberg 1970]. This pilot scheme pression wave reflects from the free surface. The wave have been used for a long time, but this original meth- 243 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 od of determining the tensile stress time profile was place, only initial manifestations of fracture in the form reduced to more simple scheme. Usually in most tests, of small cracks are observed. In the specimens de- the suprathreshold load pulses were implemented. stroyed without fracture delay, a main crack expands In this case, the dynamic strength of material can be across the total specimen width. The fracture delay characterized by the value of the tensile stress corre- effect is explained in the frames of the structure-tem- sponding to the time when the fracture occurs. Most poral approach. The fracture incubation time for the researchers estimate this critical value of the tensile studied steel is determined. This allows predicting the stress by a simple formula and interpret it as a spal- spallation phenomenon and the stress level at the time lation strength of material whatever experiments per- moment of fracture for given time profile of stress. formed. If the compressive wave initiates the threshold fracture References pulse, spallation occurs at the moment of time when Broberg, K. (1999): Cracs and Fracture – Cambridge the tensile stress in the spall cross-section is decreas- Univercity Press; Cambridge. ing and even can vanish. This effect is referred to as Zlatin, N.A., et. al (1986) On brittle solid delay frac- the fracture delay. In this case, the critical tensile stress ture. – Journal Tech. Phys. 56 (2), 403-406. given by the simple formula cannot be considered as Berezkin, A.N. et. al (2000) Effect of Delayed Crack the only characteristic of the spallation strength. The Nucleation – Doklady Physics, Vol. 45, No. 11, 2000, fracture delay effect was experimentally observed by pp. 617–619 Berezkin who studied fracture of notched specimens Petrov, Y.V. & Sitnikova, E.V. (2004) Dynamic Cracking under dynamic tension. Resistance of Structural Materials Predicted from In the present work, new experimental data on spal- Impact Fracture of an Aircraft Alloy - Technical Phys- lation in nitrogen steel are obtained and analyzed ics, Vol. 49, No. 1, pp. 57–60. with the use of the original methodic of Zlatin and Pugachev. In the tests when the fracture delay took Dynamic fracture of concrete: Experimental and numerical studies on compact tension and L- specimen JOŠKO OŽBOLT1, UWE MAYER2, NATALIJA BEDE3, AKANSHU SHARMA1 1IWB, University of Stuttgart, Germany 2MPA, University of Stuttgart, Germany 3Faculty of Civil Engineering, University of Rijeka, Croatia It is well known that in concrete structures the re- complex fracture behavior of concrete under high sistance, failure mode, crack pattern and crack ve- loading rates. The simulations performed on compact locity are strongly influenced by loading rate. The rate tension (CT) specimen (Ožbolt et al., 2011) high- dependent response of concrete is controlled through lighted the phenomenon of crack branching at high three different effects: (i) through the rate depend- loading speeds, while the simulations on L-specimen ency of the growing micro-cracks (influence of inertia (Ožbolt and Sharma, 2012) brought out the influence at the micro- crack level), (ii) through the viscous of loading rate on direction of crack propagation. behaviour of the bulk material between the cracks (vis- In order to confirm the findings of numerical study and cosity due to the water content) and (iii) through the to obtain the experimental evidence on dynamic frac- influence of inertia of different kind, e.g. structural in- ture of concrete, experiments were performed on ertia, inertia due to the softening or hardening of the both CT-specimen and L-specimen. The experiments material or inertia related to the crack propagation. confirm the results of previously performed numerical From the numerical point of view, assuming macro or predictions. meso scale analysis, the first two effects can be ac- The phenomenon of crack branching, as predicted by counted for by the rate dependent constitutive law. numerical studies, was reproduced experimentally for Assuming that the resolution of underlying spatial dis- CT-specimen. The evaluation of test and numerical re- cretization is fine enough, the third effect should be sults show that for strain rates of approximately above automatically accounted for through dynamic analy- 50/s, crack branching occurs. This phenomenon is re- sis where the constitutive law interacts with inertia lated directly to the sudden and progressive increase forces. of resistance and is controlled primarily by inertia. Recent numerical simulations performed on plain For L-specimen, the experiments confirm the influence concrete specimens showed very interesting and of loading rate on the direction of crack propagation 244 Talks Topic G 1: Fracture mechanics as numerically predicted. For quasi- static load, the tests can be used to check whether the numerical crack tends to propagate horizontally, perpendicular model is able to realistically predict complex phe- to the loading direction. However, with increase of nomena related to dynamic fracture of concrete. the loading rate the crack propagation tends to get vertical, parallel to the loading direction. References The comparison between numerical and experimen- Ožbolt, J., Sharma, A. and Reinhardt, H.-W. (2011): tal results proves that relatively simple modeling ap- Dynamic fracture of concrete-compact tension proach based on continuum mechanics, rate depend- specimen, International Journal of Solids and Struc- ent microplane model and standard finite elements tures, 48(10), 1534–1543. is capable to realistically predict complex phenomena Ožbolt, J. and Sharma, A. (2012): Numerical simula- related to dynamic fracture of concrete and no spe- tion of dynamic fracture of concrete through uni- cial criterion is required to capture crack branching, axial tension and L-specimen, Engineering Fracture change in crack propagation or progressive increase Mechanics, 85, 88–102. of apparent strength. The presented, relatively simple, Multiscale model of the dynamic tensile fracture of solid and molten metals: molecular dynamics and continuum mechan- ics Alexander Mayer, Vasiliy Krasnikov, Polina Mayer Chelyabinsk State University, Chelyabinsk, Russia We report our progress in development of a multiscale model of fracture of the uniform solid metal, which in- theoretical model of fracture of solid metals and metal cludes the model of voids growth and the equation of melts at the high-rate tension. The model is based on the voids nucleation (due to the thermal fluctuations). our previous works (Mayer & Krasnikov, 2011; Mayer The fracture of uniform metals (homogeneous mode et al. 2013; Mayer et al. 2014). It describes the dynam- of fracture) makes sense only for the ultrahigh strain ic deformation of the material on the macrolevel with rates–more than 100/µs. At the lower strain rates, the use of the mechanics of continua; meanwhile, the the initial defects of the material microstructure play evolution of ensembles of microdamages (cavities, a dominant role and decrease the material strength cracks) is described on the microlevel with the use of (transition to the heterogeneous mode of fracture). the equations of nucleation, growth and interaction of For melts, the multiscale model is the most simple and damages; these equations supplement the macroscop- allows us to understand more clearly the processes in ic description. Equations for evolution and nucleation solids as well. Using of the literature data on the sur- of microdamages and parameters of these equations face tension and viscosity of melts allows us to get a are obtained from the results of simulations on the correspondence between the continuum description basis of the molecular dynamics (MD) and continuum and MD. With the use of the model, we calculated mechanics. the strength of the uniform melts of Al, Cu, Fe and Pb We present the results of MD simulations and con- within a wide range of strain rates (from 1-10/ms to tinuous modeling of the voids growth in solid metals 1-100/ns) and temperatures (from melting temper- at tension. Mechanism of growth consists in the plas- ature to 70-80% of critical temperature). Within the tic deformation in the void vicinity. At the high strain range of the strain rates of 1-100/µs, a homogeneous rates (>10-100/µs), the plastic flow starts from the nu- nucleation mode can be realized, in which the dynamic cleation of dislocations near the void surface. At the strength of a melt can be comparable or even higher moderate strain rates (<10/µs), the initially existing than the strength of the same solid metal at room tem- dislocations in the material are enough for providing perature. We proposed a schema of experiment for of the required rate of the plastic deformation; the dis- measurement of the tensile strength of uniform metal location density are increasing due to multiplication of melts. the existing dislocations. For description of the voids The work is supported by the grant from the Russian dynamics, we propose the dislocation model, which is Science Foundation (Project No. 14-11-00538). based on our previous results (Krasnikov et al. 2011, Mayer et al. 2013). The model is verified and the mod- References el parameters are fitted on the basis of the MD and Mayer, A.E. & Krasnikov, V.S. (2011): Copper spall frac- continuum simulation results. We present a multilevel ture under sub-nanosecond electron irradiation. – 245 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Engng Fract. Mech., 78: 1306–1316. under ultrashort intensive electron or laser irradia- Mayer, A.E., Khishchenko, K.V., Levashov P.R. & May- tion. – Procedia Mat. Science, 3: 1890–1895. er, P.N. (2013): Modeling of plasticity and fracture Krasnikov, V.S., Mayer, A.E. & Yalovets, A.P. 2011: of metals at shock loading. – J. Appl. Phys, 113: Dislocation based high-rate plasticity model and its 193508. application to plate-impact and ultra short electron Mayer, A.E., Mayer, P.N. & Krasnikov, V.S. (2014): Dy- irradiation simulations. – Int. J. Plast., 27: 1294– namic fracture of metals in solid and liquid states 1308. Stage I fatigue crack studies in order to validate the disloca- tion-free zone model of fracture for bulk materials Florian Schäfer, Michael Marx, Horst Vehoff Saarland University, Dep. Materials Sciences and Engineering, Saarbrücken, Germany Stage I fatigue cracks are commonly described by the compared to the calculated distribution function of the model of Bilby, Cottrell and Swinden (BCS-model). DFZ-model proposed by Chang et al. The additionally However, since several experimental investigations measured microscopic friction stress of the disloca- have shown a dislocation-free zone (DFZ) in front of tions is then used to calculate the influence of grain crack tips, it is necessary to validate the new DFZ-mod- boundaries on the dislocation density distribution in el and to examine the deviations to the BCS-model. front of stage I cracks. The calculation is done by the Therefore the dislocation density distribution is de- extended DFZ-model of Shiue et al. and compared with rived from height profiles of slip lines in front of stage the measured distribution function in polycrystalline I fatigue cracks in CMSX4® single-crystals measured by specimens. Finally the crack tip sliding displacement as contact mode atomic force microscopy. This is possi- a measure for the crack propagation rate is compared ble, because the cracks are initiated at notches milled for the DFZ-model and the BCS-model with the exper- by focused ion beam technique directly on slip planes imentally revealed values. The important result: The with a high Schmid factor. Consequently, the directions often used BCS-model does not reflect the experimen- of the Burgers vectors are well known and it is possible tal measurements. On the contrary, the DFZ-model re- to calculate the dislocation density distributions from flects the measurements at stage-I-cracks qualitatively the height profiles. The measured distributions are and quantitatively. 246 Talks Topic G 2: Fracture mechanics Talks Topic G 2: Fracture mechanics 247 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 The Mechanics of Bridged Fatigue Cracks Jamie J. Kruzic School of Mechanical, Industrial, and Manufacturing Engineering, Oregon State University, Corvallis, USA Crack bridging is an effective mechanism for achiev- methods for determining bridging stress distributions ing high toughness and strength in many ceramics are compared [5]. Finally, it is shown how experimen- and composites [1]. However, this mechanism results tally measured fatigue data for realistic semi-elliptical in a crack size dependence for the fracture properties surface cracks agrees well with predictions based on (R-curve effect) and fatigue properties (small crack ef- quantitative bridging zone characterization [3,4]. Over- fect) when the crack size is on the order of the bridging all, it is expected that this methodology can be extend- zone size [2]. Since brittle materials can only tolerate able to cover a wide range of materials toughened by small crack sizes, making accurate fatigue failure pre- crack bridging, including ceramics, intermetallics, com- dictions requires approaches that account for crack size posites, and biological materials. effects. In this presentation, it will be described how fatigue threshold R-curves may be used to understand References and predict the fatigue behavior of bridging toughened [1] P.F. Becher, J. Am. Ceram. Soc., 74 255 (1991). materials. In this study, fatigue threshold R-curves are [2] J.J. Kruzic, R.M. Cannon, R.O. Ritchie, J. Am. Ceram. determined for bridging toughened Al2O3 and Si3N4 ce- Soc., 87 93 (2004). ramics and then are used to make fatigue endurance [3] S. Gallops, T. Fett, J.W. Ager III, J.J. Kruzic, Acta Ma- strength predictions for realistic semi-elliptical surface ter., 59 7654 (2011). cracks [3,4]. Furthermore, it is shown that the fatigue [4] R.B. Greene, S. Fünfschilling, T. Fett, M.J. Hoff- threshold R-curve can be determined by quantifying mann, J.J. Kruzic, J. Am. Ceram. Soc., 97 577 (2014). the bridging stress distribution for conventional long [5] R.B. Greene, S. Gallops, S. Fünfschilling, T. Fett, crack compact tension specimens without the need for M.J. Hoffmann, J.W. Ager III, J.J. Kruzic, J. Mech. difficult small crack experiments [3,4]. Also, different Phys. Solids, 60 1462 (2012). On the need to reconsider fatigue crack growth at negative stress ratios Christoper Benz, Manuela Sander University of Rostock, Institute of Structural Mechanics, Germany It is common practice that negative stress ratio load- lished to use K (ΔK or Kmax) and a constant value of R ings of fatigue cracks are defined by K (ΔK or Kmax) and to define the loading conditions for both positive and R < 0. But, this does not assure comparability of the negative stress ratios. However, some works claimed loading conditions at the crack tip. There are several that K ( ΔK or Kmax) and R are not suitable to define the indications and even evidence in different literature crack tip loading at negative stress ratios and did pro- works. Therefore, within this contribution well known vide alternatives. Yu, Topper and Au [Yu & Topper & facts, selected literature results and additional results Au 1984)] stated already in 1984 ”When compressive are combined to illustrate the necessity to use a sepa- stress is present in the load cycle the crack growth rate rate crack tip loading parameter for the minimum load depends on the maximum stress intensity and mini- at negative stress ratios. mum stress rather than on maximum stress intensity There is a contradiction in literature regarding fatigue and stress ratio.” Zhang et. al performed several finite crack growth at negative stress ratios. On the one hand element analysis [Zhang et al. 2008]] and they showed there are a lot of results for negative stress ratio load- that Kmax and R does not correlate with the local crack ing conditions. The results comprise numerous da/dN- tip loading at negative stress ratios. They also suggest- ΔK-curve for negative stress ratios and several variable ed to use a stress based parameter instead. More re- amplitude loading investigations. On the other hand, cently Benz and Sander [Benz & Sander 2014] suggest- there are neither basic information regarding the crack ed to use the parameter σtip to describe the minimum tip loading condition at tension-compression loading crack tip loading at negative stress ratios. However, the in textbooks nor detailed information regarding test- situation is quite difficult since there are so many data ing procedures in the standards. Therefore, it is estab- based on the established way and the literature infor- 248 Talks Topic G 2: Fracture mechanics mation on the alternatives is quite hidden. Therefore, References the different contributions on this topic are intensivly Yu, M.T., Topper T.H., Au P. (1984): The effects of discussed, interpreted and complemented by addition- stress ratio, compressive load and underload on the al considerations and results. threshold behavior of a 2024-T351 aluminum alloy? An analysis of the proposed concepts to describe the – In: Fatigue 84: proceedings of the 2nd Internation- minimum crack tip loading at negative stress ratios al Conference on Fatigue: 179-90 reveals that they are quite similar in the basic idea. Zhang J. et al. (2008): Elastic–plastic finite element However, it is shown that σtip can be interpreted as a analysis of the effect of compressive loading on generalization of the former concepts. It will be shown crack tip parameters and its impact on fatigue crack that this concept is not in conflict with the crack closure propagation rate. – In: Engineering fracture me- concept. A discussion on the consequences for fracture chanics 75(18):5217–28. mechanical analyses reveals the need to reconsider ne- Benz C., Sander M. (2014): Fatigue crack growth test- gative stress ratios in order to assure the reliability of ing at negative stress ratios: Discussion on the com- fracture mechanical predictions. parability of testing results. – In: Fatigue & fracture of engineering materials & structures 37(1 ): 62–71. Effect of adjacent small defects on fatigue limit of steels Mari Åman1, Saburo Okazaki2, Hisao Matsunaga3,4, Gary Marquis1 1Department of Applied Mechanics, Aalto University, Finland 2Graduate school of Kyushu University, Fukuoka, Japan 3Department of Mechanical Engineering, Kyushu University, Fukuoka, Japan 4International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Fukuoka, Japan The fatigue strength of a loaded component containing bination of (d1, h1, s) = (200, 200, 50) µm and (d2, h2, multiple material defects is significantly influenced by s) = (100, 100, 50) µm, the defects coalesced and the the proximity of the defects. In the most simple case crack became non-propagating at the fatigue limit, i.e., of two adjacent defects, the stress concentration is two defects together behaved as a single defect in view enhanced depending on the distance between the de- of the fatigue crack threshold. It has been suggested fects. Once cracks emanate from interacting defects, that, in such a case, the fatigue limit should be evalu- stress intensity factors of the cracks also interact and ated by the effective defect size estimated by a contour increase depending on the crack lengths and space be- that envelopes the two defects (Murakami 2002). In tween the defects. In order to investigate the interac- accordance with the aforementioned considerations, tion effect of defects on the fatigue limit of annealed the fatigue limits for various combinations of d, h and s medium carbon steel JIS-S45C, two adjacent holes were in good agreement with the prediction by the pa- were drilled into the surface of round specimens prior rameter model. A successive observation by the plastic to tension-compression fatigue testing. The diameter replica method manifested that fatigue crack growth (d) and depth (h) of the holes varied from 100 µm to suddenly accelerated soon after coalescence. In our 200 µm while the spacing (s) between the two holes presentation, in addition to the results of JIS-S45C, ranged from 0.5d to 1.5d. Fatigue limits obtained for similar results for the other type of steel with higher various combinations of d, h and s were compared strength level will also be shown. The series of exper- with the predicted values obtained by the parameter imental findings obtained in this study are necessary model (Murakami & Endo 1983). In all the cases, fa- to improve the accuracy of the fatigue limit evaluation tigue limits were determined by the non-propagation for various materials, such as cast irons, cast steels and condition of cracks emanating from the holes. The con- cast aluminium alloys, that contain naturally occurring cept of a critical spacing between the defects, scr, at defects which are detrimental to fatigue strength. which the interaction effect can be ignored has been studied. Murakami et al. determined analytically that References if the spacing between two defects is larger than the Murakami, Y. & Endo, M. (1983): Quantitative evalua- diameter of the smaller of the defects, the interaction tion of fatigue strength of metals containing various effect is negligible (Murakami & Nemat-Nasser, 1982, small defects or cracks. Eng. Fract. Mech. 17, 1-15. Murakami 2002). The experimental results from this Murakami, Y. (2002): Metal Fatigue: Effects of Small study are in good agreement with this proposal. For Defects and Nonmetallic Inclusions , Elsevier, UK, example, in the combination of (d1, h1, s) = (d2, h2, s) = ISBN: 0-08-044064-9, p.17-22. (100, 100, 100) µm, the non-propagating cracks did not Murakami, Y. & Nemat-Nasser, S. (1982): Interacting coalesce at the fatigue limit, i.e., each defect behaved dissimilar semi-elliptical surface flaws under tension as an individual defect. On the other hand, in the com- and bending. Eng. Fract. Mech 16(3), 373-386. 249 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Comparison between three fatigue damage models and experimental results for composite materials submitted to spectrum loading Mohammed Bousfia, M. Aboussaleh1, B. Ouhbi2, R.Boukhili3 1Equipe Mécanique et Ingénierie Intégrée (MII), ENSAM Meknès, Morocco. 2Equipe d’Analyse Mathématique et Simulation Numérique des problèmes en mécanique. ENSAM. Morocco. 3Centre of Applied Research on Polymers Mechanical Engineering Department hole Polytechnique de Montreal. • The theme that we have treated here is about phenomenon of random fatigue of composite • Linear damage model based on the law of Miner, structures. • Damage mathematical expectancy E (t), • The failure mode on which we focused in our work • Stiffness degradation model, is that of inter-laminar fracture delamination. Second time, following an analysis of the results, we • Next to experimental results, we have presented found that the three models mentioned above are three models for predicting damage of structures close to the experimental results. We see that the cor- in order to compare them to test results. relation is the best for the stiffness degradation model. • The effect of the standard deviation of the predic- On the other hand, the effects of load sequence and tions of the life of composites is also highlighted in interaction are not taken into account in linear damage the last part of the paper. model, which can lead to some difference between the Thanks to their excellent fatigue resistance and low model predictions and experimental results. weight ratio, today; composite materials are of great Finally, we had to study the effect of standard deviation importance in humanity life, either in civil or military on the life of composite laminates. For this we calculat- fields such as aerospace, automotive, marine … and as ed the lifetime for various values of sigma and various is usual, each material reaches failure towards the end average amplitudes of the applied load. Interpolating of his life which is manifested by the occurrence of frac- the data obtained led us to an equation linking lifetime tures. Until now, researchers put their efforts into ser- of structures to standard deviation. vice in order to achieve accurate and general models for predicting damage of this mysterious material. On References our side, we compared three fatigue damage models in M. Aboussaleh and R. Boukhili. ‘‘Life Prediction for order to see the most accurate and consistent with our Composite Laminates Submitted to Service Loading experimental results. Throughout the work, we adopt- Spectra’’. June 1998; Vol. 19; pp 241-245. ed a stationary ergodic Gaussian random loading. Adden S, Horst P. ‘‘Stiffness degradation under fatigue First, we conducted a thorough study of the inter- in multiaxially loaded non-crimped-fabrics’’. Int J laminar fracture of composite laminates subjected to Fatigue 2010; 32:108–22. stochastic loads. The choice of this failure mode was Yung-Li Lee, Tana Tjhung. ‘‘Chapter 3 - Rainflow Cycle inspired by the fact that this failure mode is most pre- Counting Techniques’’. Metal Fatigue Analysis Hand- dominant among others; moreover, it is more danger- book 2012, pp 89-114. ous because it’s invisible and undetectable and occurs SR. Reid and G. Zho. ‘‘Impact behaviour of fibre-re- suddenly between the layers of material. The results of inforced composite materials and structures’’. CRC the experiments carried out with graphite epoxy com- Press; 2000 posite laminates [± 45/0/90]3s, were compared to the predictions of three models namely: 250 Talks Topic G 2: Fracture mechanics Experimental and numerical analysis of damage in random fibrous networks E. Sozumert1, E. Demirci1, M. Acar1, B. Pourdeyhimi2, V. V. Silberschmidt1 1Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Leicestershire, UK 2Nonwovens Cooperative Research Center, North Carolina State University, Raleigh, NC, USA Fibrous networks are ubiquitous: they can be found in their actual alignment. The new developed model also various engineering applications as well as in biologi- incorporates fibre-to-fibre interactions. A good correla- cal tissues. Due to complexity of their random micro- tion between the obtained experimental data and sim- structures, anisotropic properties and a high extent of ulations results was observed, and this work revealed stretching, their deformation and damage behaviours a significant effect of fibre interactions on damage evo- are rather cumbersome and need proper analysis and lution (together with their orientation). simulations. Though, in the literature, there are nu- merous studies focusing either on numerical simula- References tions of fibrous networks or explaining their damage Hou, X., Acar, M. & Silberschmidt, V.V. (2009) 2D finite mechanisms at micro- or meso-scale, the used models element analysis of thermally bonded nonwoven usually do not incorporate actual random material’s materials: Continuous and discontinuous models, microstructure and failure mechanisms. Comput. Mater. Sci. 46: 700–707. The microstructure of fibrous networks – together with Hou, X., Acar, M. & Silberschmidt, V.V. (2011) Non-uni- usually highly non-linear mechanical behaviour of their formity of deformation in low-density thermally single fibres – is responsible for specific features of in- point bonded nonwoven material: effect of micro- itiation of damage, its spatial localization and ultimate structure. J. Mater. Sci. 46: 307–315. failure. Complex scenarios of realisation of damage Sabuncuoglu, B., Acar, M. & Silberschmidt, V.V. (2011) processes at large extensions are defined by these fea- Parametric code for generation of finite-element tures but they are not studied sufficiently. model of nonwovens accounting for orientation An experimental programme of this study included distribution of fibres. Int. J. Numer. Meth. Engng. tensional tests of notched and non-notched specimens 94: 441–453. of nonwoven fabrics were experimentally tested at dif- Farukh, F., Demirci, E., Sabuncuoglu, B., Acar, M., ferent strain rates. To study anisotropy of the deforma- Pourdeyhimi, B. & Silberschmidt, V.V. (2014) Numer- tion and damage properties (linked to a specific type ical analysis of progressive damage in nonwoven of an orientation distribution function of fibres), five fibrous networks under tension. Int. J. Solids Struct. types of specimens, cut at 0⁰, 30⁰, 45⁰, 60⁰ and 90⁰ to 51: 1670-1685. a machine direction, were investigated. Farukh, F., Demirci, E., Acar, M., Pourdeyhimi, B. & To emulate the real-life microstructure in a finite-ele- Silberschmidt, V.V. (2014) Large deformation of ment model, curled fibres were introduced to capture thermally bonded random fibrous networks: micro- geometric nonlinearity. The orientation distribution structural changes and damage, J. Mater. Sci. 49: function for fibres obtained from X-ray micro comput- 4081-4092. ed-tomography images was considered to introduce 251 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic G 3: Fracture mechanics 252 Talks Topic G 3: Fracture mechanics A boundary finite element for anisotropic/piezoelectric ma- terials containing multiple cracks Chyanbin Hwu, Shao-tzu Huang National Cheng Kung University, Tainan, Taiwan, R.O.C. The Green’s function for the problem of a two-di- nodal tractions on the boundary are calculated from mensional linear anisotropic elastic solid containing a the original system of equations of boundary element. straight crack has been obtained analytically by using Like the calculation of conventional boundary ele- Stroh’s complex variable formalism (Hwu, 2010). Us- ment, if all the values of tractions and displacements ing the Green’s function expressed in terms of Stroh’s on the boundary are determined, the values of dis- formalism, same mathematical equations can be em- placements, strains and stresses at any interior point ployed to the piezoelectric materials by just expanding can be calculated from the boundary integral equation the dimension of corresponding matrix to include the by setting the free term coefficients to be an identity piezoelectric effects (Hwu and Ikeda, 2008). The use of matrix (Brebbia, et al., 1984). Unlike the conventional this Green’s function leads to a boundary element for a method which usually needs very fine meshes near the two-dimensional anisotropic or piezoelectric solid con- crack tip, in this paper the stress intensity factors of the taining a single straight crack. The main feature of this crack are evaluated by using only the remote bounda- special boundary element is that no meshes are need- ry displacements and tractions (Hwu and Liang, 2000). ed along the boundary of cracks since the traction-free To show the accuracy and efficiency of the proposed boundary conditions are satisfied exactly. boundary finite element method, several numerical ex- In this paper, in order to extend this boundary element amples are executed and compared with the solutions to treat the problems with multiple cracks, the ele- obtained by analytical solutions and the commercial ment is transformed into an equivalent finite element finite element software. by using the relation between element nodal force of finite element and surface traction of boundary ele- References ment (Hwu, et al., 2014). After the transformation, all Brebbia, C.A., Telles, J.C.F. and Wrobel, L.C. (1984): the elements are assembled together by following the Boundary Element Techniques, Springer, New York. rule of finite element method, and the compatibility Hwu, C. and Liang, Y.C. (2000): Evaluation of Stress and equilibrium considered in the conventional sub- Concentration Factors and Stress Intensity Factors region technique can then be satisfied automatically. from Remote Boundary Data, International Journal Note that like the combination employed in the subre- of Solids and Structures, 37(41): 5957-5972. gion technique, to be compatible with the fundamen- Hwu, C. and Ikeda, T. (2008): Electromechanical Frac- tal solution the system of equations for each subregion ture Analysis for Corners and Cracks in Piezoelectric is obtained based upon the local coordinate with the Materials, International Journal of Solids and Struc- origin located at the crack center and the coordinate tures, 45: 5744-5764. axes parallel and normal to the crack surface. In order Hwu, C. (2010): Anisotropic Elastic Plates, Springer, to combine the system of equations for the whole re- New York. gion, a commonly-based global coordinate should be Hwu, C., Li, C.C. and Huang, S.T. (2014): Coupling of used, and to save computational time the transforma- Boundary and Finite Elements for the Problems of tion of matrices are suggested to be performed at the Multiple Polygon-like Holes, Advances in Boundary nodal level, instead of the subregion level. Elements & Meshless Techniques XV, 275-280, Flor- After getting the nodal displacements and nodal forc- ence, Italy. es by the system of equations of finite element, the 253 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Effect of micromorphology on crack growth in cortical bone tissue: X-FEM study Mayao Wang1, Xing Gao1, Adel Abdel-Wahab1, Simin Li1, Elizabeth A. Zimmermann2, Christoph Rie- del2, Björn Busse2, Vadim V. Silberschmidt1 1Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Leicestershire, UK, 2University Medical Center Hamburg-Eppendorf, Hamburg, Germany Bones play a key role in supporting a body and protect- istics on crack propagation, especially under dynamic ing internal organs. Obviously, bone fractures can have loading conditions. serious consequences, especially in cases of age-relat- In this study, random distributions of the microstruc- ed bone degeneration diseases such as osteoporosis ture in cortical bone tissue representing four different or bone diseases. Form a point of view of mechanics bone morphology groups were analysed. The obtained of materials, a cortical bone tissue can be treated as data were parameterized based on the obtained im- a natural multi-constituent composite material. At ages and processes employing a MATLAB programme, micro-level, osteons are its main structural unit; they considering such features as positions, dimensions, contain central canals known as Haversian canals and orientations and volume fractions of osteons and Hav- are randomly distributed within the surrounding in- ersian canals. Then, statistically representative models terstitial matrix. A thin layer of cement line separates of osteonal morphologies were developed and im- these two constituents. These randomly distributed ported into finite-element software used to simulate microstructural components of cortical bone define its crack propagation in microstructured bone tissues; an heterogeneity and anisotropy that have a direct impact extended finite-element method X-FEM was employed on crack propagation during dynamic loading regime for this purpose. The results from numerical simula- such as a traumatic fall or an accident. tions demonstrated that X-FEM is a powerful tool for It is well known that various factors (e.g. age, disease investigation of the effect of micro-morphology of os- etc.) can lead to a loss of bone mineral density due to teons and volumetric fraction of various microstructur- unbalanced remodelling process, significantly affecting al constituents on crack growth under dynamic loading morphology of the underlying microstructure com- conditions. ponents. As a result, morphological characteristics of osteons in cortical bone are complicated and varied in Reference different groups, such as young, healthy, aged, osteo- Bernhard A, Milovanovic P, Zimmermann EA, Hahn porosis and bisphosphonate-treated groups. According M, Djonic D, Krause M, Breer S, Püschel K, Djuric to the previous studies mechanical properties of corti- M, Amling M, Busse B. Micro-morphological prop- cal bones in four different groups demonstrate signif- erties of osteons reveal changes in cortical bone icant difference due to various geometrical factors at stability during aging, osteoporosis, and bisphos- the osteonal level. However, there is still no detailed in- phonate treatment in women. Osteoporosis Int vestigation on the effects of morphological character- 2013;24(10):2671-2680. Extended damage modelling for fracture control in modern line pipe steels Aida Nonn OTH Regensburg, Faculty of Mechanical Engineering, Germany Safety assurance against crack propagation in gas pipe- of propagating ductile fracture. Both criteria were suc- lines has been one of the major structural integrity cessfully applied for vintage pipeline material. challenges since 1960’s. Back then, a standardized Drop However, limitations of both criteria have become Weight Test (DWTT) with pressed notch was developed evident for modern line pipe steels with improved with the purpose to exclude brittle fracture initiation strength and toughness properties. With respect to and propagation by requiring minimum of 85-precent brittle fracture control, lower strength steels, such as shear area. At the same time the materials should also X65 grade, often exhibit propensity to so called ”ab- exhibit a minimum Charpy energy value estimated by normal fracture appearance” (AFA) or inverse fracture Battelle-Two-Curve Method (BTCM) to insure an arrest in DWTT characterized by ductile crack initiation at 254 Talks Topic G 3: Fracture mechanics pressed notch followed by onset of cleavage fracture. sible to identify major material, geometry and loading In this case the 85-precent shear area criterion can- parameters controlling ductile fracture propagation/ not be applied and DWTT results are declared invalid. arrest. On the other hand, two approaches have been Hence, the utilization of these steels remains signifi- considered for the fracture simulation in the transi- cantly restricted as long as no suitable tests and criteria tion region. One approach includes a simplified cleav- are provided to obviate brittle fracture. Regarding duc- age initiation criterion and another couples a ductile tile fracture control, it was shown that the minimum damage model to CZ model with traction-separation Charpy energy predicted by BTCM is not sufficient to law for brittle fracture. The material parameters can guarantee ductile fracture arrest, especially for high be estimated by comparison between experimental strength line pipe material such as X100 grade and cor- and numerical results conducted on deep and shallow rection factors have to be introduced in order to ac- notched SENB specimens. Subsequently, the calibrated count for these deviations. numerical models have been used for fracture simu- To develop a small-scale test representative of pipeline lation in DWTT and pipe models. The results can also fracture behaviour and derive an adequate fracture serve to understand mechanisms governing the frac- control criteria for new line pipe steels, it is desirable to ture in modern line pipe steels, e.g. inverse fracture be- combine both experimental efforts and take advantage haviour in DWTT, and how they are reflected in actual of numerical methods in material modelling. This pa- pipe behaviour. per shows how to reach these goals by applying an ex- tended damage mechanics approach to describe frac- Reference ture behaviour of modern steels in transition region. Scheider, I.; Nonn, A.; Völling, A.; Mondry, A. & Kalwa, The ductile fracture can be successfully captured for C. (2014): A damage mechanics based evaluation both X65 and X100 grades by modified Gurson-Tver- of dynamic fracture resistance in gas pipelines. gaard-Needleman (GTN) and Cohesive Zone (CZ) dam- Procedia Materials Science, Vol. 3: 1956-1964, age models. Based on the simulation results, it is pos- doi:10.1016/j.mspro.2014.06.315. 255 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic G 4: Fracture mechanics 256 Talks Topic G 4: Fracture mechanics Cleavage Initiation Angle for High Strength Steels under Mixed-Mode Conditions Zefeng Zhang, Xudong Qian Department of Civil and Environmental Engineering, National University of Singapore, Singapore The expected increasing number of infrastructures mode I and II condition at a low ambient temperature near the Arctic, driven largely by the global demand ( -90o ). The effective stress required in computing the on petroluem resources, anticipates the rising con- Weibull stress, which drives the opening of microc- sumption of high-strength ferritic steels as the prima- racks under a mixed-mode I and II condition, depends ry structural material. The cleavage fracture for these on a well-defined stress-based fracture criterion. This high-strength steels under the relatively low ambient paper examines three different fracture criteria, the temperature near the Artic imposes a critical threat to maximum princiapl stress, the coplanar energy release the safety of these infrastructures. The fracture tough- rate, and the modified co-planar energy release rate in ness, measured using the standard material testing computing the microscopic Weibull stresses. The angu- protocol [1], exhibits significantly lower toughness val- lar Weibull stress density ów-q cacluated following the ues than those measured at the room temperature. In three fracture criteria estimates the range of the cleav- addition, the large scatter in the measured toughness age fracture angle anticipated during a mixed-mode values drives a statistical approach in assessing the fracture test. The numerical study further investigates brittle structural failure, in contrast to the convention- the effect of the crack-front constraints (quantified by al, deterministic approach for ductile fracture. the T-stress) and the large plastic deformations on the The Weibull type statistical model has evolved over the cleavage angle. years as a widely recognized approach in estimating This paper also reports an experimental program for the probability of cleavage fracture for ferritic steels single-edge notched specimens made of the high under pure mode I loading. Wallin [2] utilized the Wei- strength steel S550 under a four-point bend and shear bull distribution to quantify the macroscopic scatter of mixed-mode condition. The experimental results with fracture toughness. Ruggieri and Dodds [4] employed different mode-mixity angles support the development the maximum principal stress to calculate the effective of a modified Weibull approach to assess the mixed- microscopic driving force for cleavage fracture, namely mode brittle fracture with an experimentally validated the Weibull stress ów . The Weibull stress ów repre- stress criterion. sents a scalar measure of the driving force for the mi- croscopic cracks in the fracture process zone. The use References of microscopic Weibull stress allows the development 1. ASTM E1921-13a (2013). Standard test method for of a uniform approach to predict the probability of frac- determination of reference temperature, To, for ture under varying levels of crack-front constriants. The ferritic steels in the transition range. ASTM Interna- Weibull stress approach has demonstrated reasonable tional, West Conshohocken, PA. success in estimating the probability of fracture for a 2. Wallin, K. (1984): The scatter in KIC-results. Eng Fract wide range of materials, reflected most recently by the Mech, 19, 1085-1093. comparison to the Euro fracture database [4]. Howev- 3. Ruggieri, C. and Dodds, R.H.Jr. (1998): Numerical er, realistic cracks in engineering structures often expe- computation of probabilistic fracture parameters rience a mixed-mode condition, which requires further with WSTRESS. Engng Comput, 15, 49-73. understanding on both the cleavage fracture angle and 4. Wasiluk, B., Petti, J.P. and Dodds, R.H.Jr. (2006). toughness assessment. Temperature dependence of Weibull stress param- This study aims to extend the probablistic Weibull eters: studies using the Euro-materials. Engng Fract stress framework to estimate the cleavage fracture Mech, 73:1046–69 angle for high-strength ferritic steels under the mixed- 257 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Experimental and numerical investigations on the crack growth stage of crane runway girders subjected to cyclic loading Philipp Rettenmeier, Eberhard Roos, Stefan Weihe, Xaver Schuler Materialprüfungsanstalt (MPA) Universität Stuttgart, Germany Numerous engineering components as railway tracks in combination with critical plane approach (Retten- or crane runways are subjected to rolling contact fa- meier2015). The numerical investigations showed that tigue (RCF) due to travelling wheel loads. RCF causes crack growth stage approximately amounts to one half non-proportional mixed mode crack tip loading (Fletch- of the total lifetime. Finally, the calculated total life- er2014) and mode II controlled or shear mode crack time was compared to experimental results until first growth (Bold1991, Otsuka1993, Otsuka1996). Tradi- through-thickness crack. tional fracture mechanic concepts dealing with mode I or tensile mode crack growth are thus not applicable References (Bold1991, Yang2014). One of the reasons is the com- Bold, P.E. & Brown, M.W. & Allen, R.J. (1991): Shear pressive stress field directly below the wheel load sup- mode crack growth and rolling contact fatigue. – pressing tensile mode crack growth (Otsuka1996). Wear 144, 307-317 The contribution is focused on the crack growth stage Fletcher, D.I. (2014): Numerical simulation of near surface of crane runway girders consisting of hot-rolled gird- rail cracks subject to thermal contact stress. – Wear 314, ers with welded rails. Cyclic tests were conducted 96-103 on full-scale crane runway girders travelled over by Forman, R. G. & Mettu, R. M. (1990): Behavior of Surface wheel loads. Fatigue crack initiation was identified at and Corner Cracks subjected to Tensile and Bending Loads the sharply notched weld root. As a consequence, de- in Ti-6Al-4V Alloy, NASA Technical Memorandum 102165 tection of crack initiation lifetime was technically not Otsuka, A. & Mori, K. & Miyata, T. (1975): The condition of feasible by non-destructive measurements due to the fatigue crack growth in mixed mode condition. – Engi- weld geometry. Therefore, a pressure system was used neering Fracture Mechanics 7, 429-439 to detect the lifetimes until first through-thickness Otsuka, A. & Aoyama, M. (1993): Mode II Fatigue under a crack (Rettenmeier2013). Shear mode fatigue crack Compressive Stress Field: a Simplified Model for Rolling growth within the weld metal was observed by frac- Contact Fatigue. – Mixed Mode Fatigue and Fracture, tographic investigations after cyclic tests. Additionally, 49-60 crack growth rate was evaluated by means of tests with Otsuka, A. & Sugawara, H. & Shomura, M. (1996): A test C(T) specimens extracted from the weld metal. method for mode II fatigue crack growth relating to a Numerical investigations were performed in Abaqus to model for rolling contact fatigue. - Fatigue & Fracture of calculate the crack growth lifetime of the crane run- Engineering Materials and Structures 19, 1265-1275 way girders. Stress intensity factors were evaluated Rettenmeier, P. & Euler, M. & Roos, E. & Kuhlmann, U. by means of modified virtual crack closure technique. (2013): Experimental investigations on the fatigue Mixed mode crack tip loading was identified. An initial strength of welded joints on full-scale crane runway gird- crack length of 1 mm was assumed for crack growth ers. – Proceedings of the 10th International Conference on calculations. Numerical calculations showed a signifi- Multiaxial Fatigue & Fracture (ICMFF10), Kyoto cant influence of mode II stress intensity factor on crack Rettenmeier, P. & Roos, E. (2015): Fatigue assessment of growth. Thus, crack growth lifetime was estimated by full-scale welded crane runway girders. – to be published shear stress intensity factor Kt introduced by Otsuka et in MP Materials Testing al. (Otsuka1975) and NASGRO equation according to Yang, Y. (2014): Linear elastic fracture mechanics-based Forman/Mettu (Forman1990). simulation of fatigue crack growth under non-propor- Subsequently, the calculated total lifetime was sepa- tional mixed-mode loading. – PhD Thesis, University of rated into crack initiation and crack growth lifetime. Darmstadt The former was estimated by MPA AIM-Life concept 258 Talks Topic G 4: Fracture mechanics Crack Path in connection with the Two-Parameter Fracture Mechanics Approach on X52 steel pipe repairing M. Hadj Meliani1,2, G. Pluvinage2, Y.G. Matvienko3 1LPTPM, TF, Hassiba Benbouali University, Chlef, Algeria 2LaBPS-ENIM, Metz, France 3Mechanical Eng. Research, Moscow, Russia The use of a composite patches for the repair of the effects of the notch aspect ratio, the type of laboratory API 5L X52 steel pipe in connection with the crack specimens (CT, SENT, DCB and RT) and the repairing path estimation are presented in this study. The method on the variation of the applied notch stress finite element method (FEM) is used to analyse the intensity factor and the T-stress at the notch tip are fracture resistance of a pipe repaired by a boron/ highlighted. The obtained results show a considerable epoxy bonded composite patch by evaluation of the decrease of the applied notch stress intensity factor in notch stress intensity factor Kρ and the non-singular the case of the repaired defect in connection with the T-stress as a constraint parameter. The use of the two crack path. The use of the composite patch reduces parameter fracture mechanics (K-T) given a described significantly the risk of fracture and increases the information’s of the crack path of the defect of a service life of the pipeline. structure with and without a reinforcing patch. The A modified Sih criterion for crack deflection in dipolar gradi- ent elasticity Ioannis D. Gavardinas, Antonios E. Giannakopoulos University of Thessaly, Civil Engineering Department, Volos, Greece In recent years, generalized or higher order (non lo- In an effort to attack crack deflection in the context of cal) continuum theories have attracted attention due dipolar gradient elasticity, an issue not attempted be- to the fact they inherently predict the so called “size fore in the relevant literature, we have revisited the effect” in the mechanical behavior of materials. This is Sih’s strain energy density criterion, based upon physi- attributed to their “constitutive” incorporation of in- cal considerations for its prevalence. At the same time, trinsic or internal material lengths. On the other hand, we concluded that other crack deflection criteria may there exist cases in which classic (local) theories of me- not be relevant. Following an analytical study, we val- chanics have failed to capture the mechanical behavior idated its applicability for dipolar gradient elastic ma- of these specific materials. The higher order theories terials. We have used a second order asymptotic strain provide enhanced models for materials with micro- energy density close to the crack tip, using the crack structure like composites, cellular materials, textiles tip fields as obtained from the asymptotic analysis of etc. The dipolar or strain gradient elasticity is one such (Gourgiotis & Georgiadis 2009) and (Aravas & Gianna- theory which was set forth by (Aifantis 1992) with the kopoulos 2009). We propose that crack deflection will introduction of a single material length, following the appear at a direction that maximizes the near-tip strain more general theory of (Mindlin & Eshel 1968). energy density along a specific line around the crack Adopting a Fracture Mechanics point of view, the issue tip. This line requires the determination of the angular of crack deflection plays a significant role. Tackling the distribution of the radial distance r around the crack crack deflection problem was historically initiated by tip, such that the first and the second order strain en- (Griffith 1920) for materials exhibiting a quasi-brittle ergy densities become comparable. The central crack type of behavior, upon the hypothesis of an energet- problem in an infinite medium is examined, for mode ic balance regarding the transition from the unbroken I, mode II and mixed mode (I+II) loading. The acquired state of a solid to the broken one. The years to come, results lead to a powerful method for predicting crack several crack deflection criteria have been stated, deflection trajectories in materials with microstructure mainly: the maximum energy release rate criterion that can be adequately modeled by dipolar gradient (Hussain et al. 1974), the maximum circumferential elasticity. stress criterion (Erdogan & Sih 1963) and the strain en- ergy density criterion (Sih 1974). 259 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Acknowledgements Gourgiotis, P.A. & Georgiadis, H.G. (2009): Plane-strain This project was implemented under the “ARISTEIA II” crack problems in microstructured solids governed Action of the “OPERATIONAL PROGRAMME FOR EDU- by dipolar gradient elasticity. – J. Mech. Phys. Solids, CATION AND LIFELONG LEARNING”, project “Fatigue of 57: 1898-1920. Materials used in Vascular Surgery-FaMaVaSu”, and is Griffith, A.A. (1920): The phenomena of rupture and co-funded by the European Social Fund (ESF) and Na- flow in solids. – Philos. Trans. R. Soc. Lond. A., 221: tional Resources. 163-198. Hussain, M.A., Pu, S.L. & Underwood, J. (1974): Strain References energy release rate for a crack under combined Aifantis, E.C. (1992): On the role of gradients in the mode I and mode II. – Fract. Anal., ASTM STP 560, localization of deformation and fracture. – Int. J. Am. Soc. Test. Mat., 2-28. Eng. Sci., 30: 1279-1299. Mindlin, R.D. & Eshel, N.N. (1968): On first strain-gra- Aravas, N. & Giannakopoulos, A.E. (2009): Plane as- dient theories in linear elasticity. – Int. J. Solids ymptotic crack-tip solutions in gradient elasticity. – Struct., 4: 109-124. Int. J. Solids Struct., 46: 4478-4503. Sih, G.C. (1974): Strain-energy-density factor applied Erdogan, F. & Sih, G.C. (1963): On the crack extension to mixed mode crack problems. – Int. J. Fract., 10: in plates under plane loading and transverse shear. 305-321. – ASME J. Basic. Eng., 85: 519-525. Cohesive laws for adhesive layers loaded in a state close to pure shear Ulf Stigh1, Anders Biel2 1University of Skövde, Skövde, Sweden 2Technical University of Denmark, Risø, Denmark By representing a thin adhesive layer with a cohesive In shear loading, the end notched flexure specimen is zone, analysis of fracture of bonded structures is great- used. This is a three-point bending test rig where the ly simplified while providing high qualitative predictive centrally applied load F is measured. In one method to capability (Carlberger et al. 2008). With this model, evaluate the experiments, only F and v at the start of only homogenized stress, deformation and damage the adhesive layer are measured (Alfredsson 2004); in measures are used to represent the state of the adhe- the alternative method, also the rotations, θA, θB and sive. The stress variables are denoted the peel stress s θC, of the loading and supporting points are measured acting in the normal direction of the surface and the (Stigh et al. 2009). The alternative expressions read shear stresses τ1 and τ2 acting in the plane of the sur- face. The work per unit surface performed by theses stresses during a deformation process is given by J 9 F 2a2 3 Fv S = +16 EB2H2 8 BH w v1 v2 (2) W = ∫σdw + ∫t dv F1 1 + ∫t2dv2 , (1) JR = (sinqA - 2sinqB + sinqC ) 0 0 0 2B Evaluations of the same experiments using these two where w, v1, and v2 denote the deformation compo- equations show good agreement. nents of the adhesive layer measured in the directions However, during the final stage of the fracture pro- of the corresponding stress components. With mono- cess, the adhesive layer swells, i.e. w > 0 (Stigh and Biel tonically increasing deformation, a pseudopotential 2014). This swelling is confined to the end of an adhe- is associated to the state of the adhesive layer. In this sive layer and it is constrained by the flexural stiffness case an evaluation of the path independent J-integral of the adherends. This shows that a compressive stress at the edge of an adhesive layer reveals that W = J. That develops during shear. is, if J is measured during an experiment, the evolution of W is also measured. If, at the same time, w, v1, and References v2 are measured, the gradient of W provides σ, τ1 and Alfredsson, K.S. (2004): On the instantaneous energy τ2. Thus, the corresponding cohesive law is measured. release rate of the end-notch flexure adhesive joint A number of test specimens and procedures have been specimen. Int. J. Sol. & Str., 41: 4787–807. developed (Stigh et al. 2010). Biel, A., & Stigh, U. (2014): Shear properties of an ad- 260 Talks Topic G 4: Fracture mechanics hesive layer exposed to a compressive load. Proc. berger, T., & Salomonsson, K. (2010): Some aspects Mat. Sci., 3: 1626-1631. of cohesive models and modelling with special ap- Carlberger, T., Alfredsson, K.S. & Stigh, U. (2008): plication to strength of adhesive layers. Int. J. Fract., FE-formulation of Interphase Elements for Adhesive 165: 149-62. Joints. Int. J. Comp. Meth. Engin. Sci. & Mech., 9: Stigh, U., Alfredsson, K.S. & Biel, A. (2009): Measure- 288-99. ment of cohesive laws and related problems. Proc. Stigh, U., Alfredsson, K.S., Andersson, T., Biel, A., Carl- ASME IMECE-10474, USA The role of Geometrically Necessary Dislocations in the frac- ture process of metallic materials Emilio Martínez-Pañeda1, Christian Niordson2 1University of Oviedo, Spain 2Technical University of Denmark, Denmark Experiments and direct dislocation simulations have In the present work, a comprehensive study of crack- shown that metallic materials display strong size effect tip fields is performed for both phenomenological and at the micron and sub-micron scales. Attributed to ge- mechanism-based SGP theories with the aim of gaining ometrically necessary dislocations (GNDs) associated insight into the role of the increased dislocation densi- with non-uniform plastic deformation, this size effect is ty associated with large gradients in plastic strain near especially significant in fracture problems as the plastic the crack. Following the work of Niordson and Redanz zone adjacent to the crack tip may be physically small (2004), a finite strain generalization is implemented in and contains large spatial gradients of deformation. a general purpose finite element code by means of an Since conventional plasticity possesses no intrinsic ma- updated Lagrangian configuration and physical implica- terial length, several continuum strain gradient plas- tions of the results are thoroughly discussed, providing ticity (SGP) theories have been developed through the an appropriate framework for damage and fracture as- years in order to model observed size effects. Most of sessment within SGP theories. them can be classified as a function of their approach: Results obtained reveal the important influence of phenomenological (Fleck and Hutchinson, 2001) or strain gradients on a wide range of fracture problems, mechanism-based (Gao et al., 1999). being particularly relevant in hydrogen embrittlement The experimental observation of cleavage fracture in models, due to the central role that the stress field the presence of significant plastic flow (Elssner et al., close to the crack-tip plays on both hydrogen concen- 1994) has encouraged significant interest in the in- tration and interface decohesion (Gangloff et al., 2014). fluence of plastic strain gradient effects on crack tip stresses and many authors have shown that GNDs near References the crack tip promote local strain hardening and lead Elssner, G., Korn, D., Rühle, M. (1994): The influence to a much higher stress level in the vicinity of the crack of interface impurities on fracture energy of UHV as compared with classical plasticity predictions. How- diffusion-bonded metal-ceramic bicrystals. Scr. ever, although large deformations take place in the vi- Metall. Mater., 31: 1037-1042. cinity of the crack, very little work has been done to Fleck, N.A., Hutchinson, J.W. (2001): A reformulation investigate crack tip fields under SGP accounting for of strain gradient plasticity. J. Mech. Phys. Solids, 41: finite strains. 1825-1857. Very recently Martínez-Pañeda and Betegón (2015), Gao, H., Huang, Y., Nix, W.D., Hutchinson, J.W. (1999): in the framework of a mechanism-based approach Mechanism-based strain gradient plasticity I. Theo- and within the finite deformation theory, quantified ry. J. Mech. Phys. Solids, 48: 99-128. the magnitude and the extension of the differences Martínez-Pañeda, E., Betegón, C. (2015): Modeling between classical plasticity and SGP stress distribu- damage and fracture within strain gradient plastici- tion predictions ahead of the crack tip. Their numer- ty. Int. J. Solids Struct. [in press] ical results revealed a significant increase in both the Niordson, C.F., Redanz, P. (2004): Size-effects in plane magnitude and the domain where GNDs significantly strain sheet-necking. J. Mech. Phys. Solids, 52: 2431- influence the crack-tip fields when finite strains are 2454. considered. This is due to the strain gradient contribu- Gangloff, R.P., Ha, H.M., Burns, J.T., Scully, J.R. (2014): tion to the work hardening of the material, that lowers Measurement and modeling of hydrogen environ- crack tip blunting and thereby avoids the local stress ment-assisted cracking in Monel K-500. Metall. Ma- triaxiality reduction characteristic of conventional plas- ter. Trans. A, 45: 3814-3834. ticity predictions. 261 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talk Topic G 5: Fracture mechanics 262 Talk Topic G 5: Fracture mechanics On the fracture toughness of bulk-metallic glasses Bernd Gludovatz1, Jamie J. Kruzic2, Marios D. Demetriou3, William L. Johnson3, Robert O. Ritchie1,4 1Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, CA, USA 2Oregon State University, School of Mechanical, Industrial, and Manufacturing Engineering, Materials Science, Corvallis, OR, USA 3California Institute of Technology, Keck Laboratory of Engineering Materials, Pasadena, CA, USA 4University of California, Department of Materials Science and Engineering, Berkeley, CA, USA The excellent combination of properties like high ent loading conditions, specifically deep-cracked bend- strength, low stiffness and high hardness together with ing vs. edge-cracked tension, to understand influences the ease of processing and near net-shape castability of sample size and stress-state on the measured frac- make bulk-metallic glasses (BMGs) candidate materials ture toughness of BMGs, as well as to determine the for many structural applications. Their fracture tough- origin of the large variations in toughness often found ness, however, can vary over a wide range (generally for these materials. between 10 and 200 MPa.m1/2) and in terms of ductil- ity, BMGs behave entirely different whether they are References loaded in tension, compression or bending. Where- Demetriou, Marios D., Maximilien E. Launey, Glenn as ductility is rather limited in tension/compression, Garrett, Joseph P. Schramm, Douglas C. Hofmann, BMGs can be quite ductile in bending. Standard frac- William L. Johnson, and Robert O. Ritchie. “A Dam- ture-toughness tests are normally done on “bending” age-Tolerant Glass.” Nature Materials 10, no. 2 (Jan- geometries (three-point bending, compact-tension uary 9, 2011): 123–28. specimens) but it is not clear how the behavior in Gludovatz, Bernd, Steven E. Naleway, Robert O. Rit- BMGs under these constrained stress-states relates to chie, and Jamie J. Kruzic. “Size-Dependent Fracture that in tension; as such, the extent of validity of non- Toughness of Bulk Metallic Glasses.” Acta Materialia linear-elastic fracture mechanics to characterize their 70 (May 15, 2014): 198–207. toughness is in question. He, Qiang, and Jian Xu. “Locating Malleable Bulk Me- Here, we report on a systematic study to compare the tallic Glasses in Zr–Ti–Cu–Al Alloys with Calorimetric toughness of three different, Zr-based glasses – one Glass Transition Temperature as an Indicator.” Jour- low toughness (< 50 MPa.m1/2), one medium and one nal of Materials Science & Technology 28, no. 12 high toughness (>150 MPa.m1/2) – tested under differ- (December 2012): 1109–22. Damage & Fracture Toughness of Fibrous Dual-Phase Steels for Automotive Applications Karim Ismail1, Thomas Pardoen1, Pascal J. Jacques1, Laurence Brassart1, Astrid Perlade2 1UCL, iMMC, Louvain-la-Neuve, Belgium 2ArcelorMittal, Maizières-lès-Metz, France Dual-Phase steels have long been used in the automo- ture and damage mechanisms is essential to develop tive industry due to their excellent mechanical proper- advanced steels with superior forming ability. ties in terms of strength and ductility, as well as their Dual-Phase steels are usually processed following an low processing cost. The good compromise between intercritical annealing which generally leads to equi- strength and ductility results from the very different axed martensite inclusions. An alternative heat treat- properties of the constituent phases comprising duc- ment, consisting of a double annealing first proposed tile ferrite and hard martensite. N.J. Kim and G. Thomas [1] brings about fibrous mar- In contrast with their plastic flow properties, the frac- tensite inclusions. A very recent study on such steels ture toughness of Dual-Phase steels (quantified by KIc shows that this fibrous microstructure can potentially or JIc) has been far less investigated. Common values of lead to a very high fracture toughness, while retaining the fracture toughness are around 100[kJ.m-2] or even good properties in terms of strength and ductility [2]. lower; but seldom exceed the 200[kJ.m-2]. However, a The general objective of this research is to investigate minimum level of fracture toughness is required to pre- the fundamental damage mechanisms that govern the vent the propagation of small edge damage or cracked fracture toughness of Dual-Phase steels. Our approach zones induced by cutting. Therefore, unravelling the is based on the processing of microstructures in which relationship between fracture toughness, microstruc- parameters are varied one by one. In particular, both 263 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 equiaxed and fibrous microstructures were investigat- ed the basis for the development of a micromechan- ed in the form of thin sheets. ics-based predictive model of the toughness of Du- The Essential Work of Fracture (EWF) method [3] was al-Phase steels. used to quantify the work per unit area needed at the crack tip for material failure separating it from the to- References tal work expended for material failure. An extension of [1] N.J. Kim, G. Thomas (1981): Met. Trans A , 12: 483-489. the EWF method also allows us to separate the work [2] A.-P. Pierman (2013): Doctoral Thesis. of necking from the work of damage [4]. In addition, [3] B. Cotterell, J.K. Reddell (1977): Int. J. Fracture, 13: tomography experiments were conducted in order to 267-277. study the nucleation and growth of cavities within the [4] T. Pardoen, F. Hachez, B. Marchioni, P.H. Blyth, A.G. sheets. These preliminary measurements constitut- Atkins (2004): J. Mech. Phys. Solids 52: 423-452. New insights on the physically correct application of the J-in- tegral for characterizing fatigue crack growth in elastic–plas- tic materials Walter Ochensberger1,2, Otmar Kolednik1 1Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben, Austria 2Materials Center Leoben Forschung GmbH, Austria The majority of failures in technical applications can be extension occurs by an increment after each load cycle. attributed to fatigue crack propagation. Cracks under The maximum load is varied so that small- and large- low-cycle fatigue conditions and short fatigue cracks scale yielding conditions prevail in the specimen. Three cannot be assessed with the conventional stress inten- different load ratios, for zero-tension, pure tension and sity range DK-concept, since linear elastic fracture me- tension-compression loading, are investigated. chanics is not valid. For such cases, Dowling and Begley Theoretical considerations and comparisons with the (1976) proposed the experimental cyclic J-integral DJexp cyclic crack tip opening displacement ∆δt show that for the characterization of the fatigue crack growth the cyclic, incremental plasticity J-integral for a contour rate. However, severe doubts exist concerning the enclosing the active plastic zone of the moving crack application of DJexp. The reason is that DJexp relies, like tip, DJepactPZ, reflects the magnitude of the “driving the conventional J-integral, on deformation theory of force” for fatigue crack propagation. The results show plasticity, which idealizes the elastic–plastic material to that the parameter DJepactPZ is also able to reflect be nonlinear elastic. Therefore, fundamental problems crack growth retardation after application of a single appear due to the strongly non-proportional loading tensile overload. The validity of the experimental cyclic conditions during fatigue crack propagation. J-integral DJexp is also clarified: DJexp is, in principle, The configurational force concept provides a possible correct for stationary fatigue cracks, but does not ex- solution to this problem, since it enables the deriva- actly quantify the “driving force” during fatigue if crack tion of the J-integral for elastic–plastic materials with extension occurs. incremental theory of plasticity, called Jep (Simha et al. 2008). This Jep overcomes the theoretical restrictions of References the conventional J-integral and is physically appropri- Dowling, N.E. & Begley, J.A. (1976): Fatigue crack ate to characterize fatigue crack propagation, however, growth during gross plasticity and the J-integral. – it is, in general, path dependent. In two recent papers, ASTM STP 590:82–103. we studied the possible application of this Jep-integral Simha, N.K., Fischer, F.D., Shan, G.X., Chen, C.R., for the assessment of the driving force for fatigue crack Kolednik, O. (2008): J-integral and crack driving growth (see Ochensberger and Kolednik 2014, 2015). force in elastic–plastic materials. – J. Mech. Phys. A driving force term in fatigue should allow the pre- Solids 56:2876–2895. diction of the crack propagation rate of a fatigue crack. Ochensberger, W. & Kolednik, O. (2014): A new basis The purpose of the current presentation is to show how for the application of the J-integral for cyclically Jep shall be used to evaluate correctly the driving force loaded cracks in elastic–plastic materials. Int. J. Frac- for fatigue crack growth, in order to characterize the ture 189:77–101. crack growth rate during fatigue. Therefore, the path Ochensberger, W. & Kolednik, O. (2015): Physically dependence of Jep is studied in numerical investigations appropriate characterization of fatigue crack prop- conducted on two-dimensional C(T)-specimens with agation rate in elastic–plastic materials using the long cracks subjected to cyclic Mode I loading. Crack J-integral concept. Int. J. Fracture (in press). 264 Talk Topic G 5: Fracture mechanics Grain Boundary Precipitation and Creep Crack Growth in polycrystalline Ni-base superalloys H. Sommer1, C. Somsen1, F. Mueller2, V. Knezevic3, N. de Boer4, J. Klöwer4, G. Eggeler1 1Institut für Werkstoffe, Ruhr-Universität Bochum, Bochum, Germany 2Chair and Institute for Materials Technology, Darmstadt University of Technology, Darmstadt, Germany 3Vallourec Research Center, Düsseldorf, Germany 4VDM Metals GmbH, Altena, Germany In the present work the creep crack growth (CCG) focused ion beam micromachining (FIB), thin foils were behavior of two polycrystalline Ni-base superalloys, cut out from the material close to the creep crack. This A617B and C263, is studied. In the microstructure of allowed to study the microstructure which governed C263 a large volume fraction of intermetallic γ’ phase CCG. The thin foils were studied using transmission and a high density of grain boundary (GB) precipi- electron microscopy (TEM). GB particles were charac- tates are observed. Significantly smaller amounts of terized using energy dispersive X-ray (EDX) analysis and γ’ phase, as well as a lower density of GB precipitates selected area electron diffraction. The density of parti- characterize the solution annealed alloy A617B. Thus, cles at the GBs was characterized by the ratio between alloy C263 exhibits better creep resistance than alloy the sum of the projected areas of GBs carbides and the A617B. However, alloy C263 shows a higher sensitivity area of the GB region which was affected by carbides. to creep crack propagation. The objective of the pres- The results of the mechanical and microstructural in- ent work is to identify the microstructural parameters vestigations suggest that the alloy with the higher den- which govern CCG. For this purpose, compact tension sity of GB carbides is less resistant against CCG. These CCG tests were performed according to ASTM E 1457. A results are discussed in the light of previous findings preliminary scanning electron microscopy investigation and areas in need of further work are highlighted. showed that CCG occurred along high angle GBs. Using Examination of Evaluation Method for Static Strength of Casting Materials by Regarding Shrinkage Porosity as Cracks: Example of AZX912 Mg Cast Alloy Yu-ki Higuchi1, Naoya Ochi2, Hiroshi Noguchi1 1Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, Fukuoka, Japan 2Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University, Fukuoka, Japan With respect to a fracture originating any defect, ferent from that of cracks. breaking strength is determined sometimes by crack As for a circumferential notch, it is reported that ten- initiation stress and sometimes by crack propagation sile strength of notched specimens is equal to that of limit stress. The crack behavior in the process of static specimens which has a crack of the same size of the fracture is controlled by mechanical conditions and ma- notch when notch tip radius is smaller than certain terial structures. Incidentally, all casting materials have value. Meanwhile, when tip radius is dull, the tensile shrinkage porosity which decreases static strength. strength depends on the tip radius. Whether tensile Since shrinkage porosity has micron order tip radius, strength depends on tip radius or not can be explained shrinkage porosity is most likely to behave as cracks in by a magnitude relationship of crack initiation stress the static fracture. Therefor the authors consider that and crack propagation limit stress. The crack initiation static strength of casting materials can be evaluated stress depends on the notch tip radius. In contrast, the from computer simulation regarding shrinkage poros- crack propagation limit stress doesn’t depend on be- ity as cracks whose area is equal to projected area of cause when a crack exists at the notch tip, stress state shrinkage porosity on the plane perpendicular to the is dominated almost only by the crack. When a notch principal stress. However, there’s no reproducibility of tip is sufficiently sharp to crack initiation stress doesn’t the shrinkage porosity for its shape and arrangements. exceed crack propagation limit stress, initiated crack at Therefore, in static fracture it should be considered the notch tip can propagate stably with the load incre- that behavior of the shrinkage porosity is possibly dif- ment. Subsequently, if applied tensile stress exceeds 265 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 crack propagation limit stress, the crack propagates any defect including shrinkage porosity. The shrinkage unstably in another moment. The authors believe that porosity as mentioned before, it appears to be need- the notch can be regarded as a simple crack in this ed that clarifying relation between defect shapes and case. On the other hand, when a notch tip is sufficient- crack behavior such as crack initiation, stable propaga- ly dull to crack initiation stress exceed crack propaga- tion and unstable propagation. tion limit stress, fracture from the notch doesn’t have In this study, tensile tests were performed to circum- a stable crack propagation step. In short, specimens ferential notched specimens with variant notch size break immediately after the crack initiation. Terefore, and tip radius. AZX912 non-combustible Mg cast alloy tensile strength depends on notch tip radius with a is adopted. In this paper, we will discuss crack behavior sharp notch, and doesn’t with a dull notch. in static fracture considering material structure. Finally The authors believe that the magnitude relationship we will examine possibility of the method that regard- of crack initiation stress and crack propagation limit ing shrinkage porosity as cracks in strength evaluation stress decides existence of stable crack propagation in of casting materials. Insight into MAG welding under constructive constraint con- ditions by means of high energy synchrotron X-ray diffraction Florian Vollert1, Jens Gibmeier1, Jonny Dixneit2, Thorben Fischer3, P.Staron3, Arne Kromm2, Thom- as Kannengiesser2 1Karlsruhe Institute of Technology (KIT), Institute of Applied Materials (IAM), Karlsruhe, Germany 2BAM Federal Institute for Materials Research and Testing, Berlin, Germany 3Helmholtz-Zentrum Geesthacht, Institute of Materials Research Hamburg, Germany Welding using low transformation temperature (LTT) in longitudinal and in normal direction to the weld line filler materials is an innovative method to mitigate in the (partially) coexisting martensite and austenite welding residual stresses. In particular due to the se- phases. The measurement results are compared to lective producing of compressive residual stresses in in-situ diffraction experiments using a conventional the weld and in the heat affected zone (HAZ) a signif- high strength weld filler material. icant enhancement of the cold cracking resistance of Due to the reduced temperature of martensite start highly stressed welded components can be expected. (MS), crucial differences in the transformation be- For the effective usage of these materials an in-depth havior are observed. In contrast to the LTT weld filler comprehension of the microstructural developments materials the conventional filler material shows higher during welding is necessary to determine the complex values of MS and faster martensite transformation ki- processes that occur during residual stress formation. netics. Solid-state phase transformation kinetics and the Regarding the LTT alloys the martensite formation evolution of thermal and elastic strains in two dif- counteracts the thermal contraction strains, which ferent modern LTT weld filler materials (one Ni- and leads to a significant decrease of the tensile strain dis- one Mn-containing alloy) are monitored in-situ at the tribution during cooling down. Therefore, in contrast HEMS (High Energy Materials Science) beamline at to the conventional filler material the LTT alloys are the synchrotron light source PETRA III in Hamburg. The found to exhibit relatively low residual strain, which is transferability to real components is ensured by using attributed to the low martensite transformation tem- a realistic MAG welding process under consideration of perature. Moreover, the LTT strain distributions, as well constructive constraint conditions. Here, two different as the directional evaluation of phase transformation, constraint conditions are considered. During welding show periodical oscillations, attended by defined alter- of multilayer joints, the local phase transformation and ation of the interference peak intensity. This transient strain evolution of each individual layer is investigated effect can be attributed to local changes in crystal- in transmission geometry using a photon energy of 100 lite orientation (grain rotation) and is differently pro- keV. Further, the changes in already welded layers are nounced for the different alloys. studied, when further layer are welded on top. Results show that the transformation kinetic is depend- Debye rings are recorded by means of an area detec- ent on the position of the welded layer. Furthermore, tor at a counting rate of 2 Hz. Evaluation of complete the strain evolution for each layer differs. This can be Debye rings in the diffraction images provides local in- attributed to both, the local chemical mixing between formation about phase fraction and transformation ki- weld filler and base material which affects the mar- netics. 15° ´cake pieces´ of the Debye rings are defined tensite formation and the constraint condition applied. and integrated to investigate the phase specific strain 266 Talks Topic G 6: Fracture mechanics Talks Topic G 6: Fracture mechanics 267 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Testing fracture toughness of britle materials via chevron- notched bend bars of microscopic length-scale Goran Zagar1, Martin Mueller1, Vaclav Pejchal1, Lionel Michelet1, Marco Cantoni2, Andreas Mortensen1 1Laboratory of Mechanical Metallurgy, Institute of Materials, EPFL, Switzerland 2 Interdisciplinary Centre for Electron Microscopy, EPFL, Switzerland Modern “small scale” technologies are in need of which the cantilever is attached to the bulk material. methods for the testing of materials for mechanical Cantilevers are deflected up to the point of fracture properties at microscopic length scales. In particular, using a nanoindentation apparatus. We find that for fracture toughness at the micron scale has been re- sufficiently thin chevron notches, the crack is regularly cently probed using samples machined by the focused initiated at the apex of the triangular ligament under a ion beam (FIB) method. FIB micromachining technique load that is lower than that corresponding to the onset allows a rather good degree of flexibility in shaping the of crack instability. Subsequent increase in load there- specimens, thus microscopic beams with straight sin- fore at first drives the crack thus created to propagate gle-edge notches have been produced and tested main- within the plane of a chevron notch in a stable manner, ly as cantilevers or in a 3 point bending-like setup. The before instability and final fracture of the specimen main concern associated to the FIB milled specimens, take place. Test data are interpreted using compliance however, is that FIB-based machining is damaging and calibration curves calculated by three-dimensional fi- modifies the specimen surface; FIB milled surfaces can nite element simulation of each beam individually, af- become amorphous doe to ion implantation and irra- ter measurement of its dimensions from SEM images. diation and/or they can be contaminated by redepo- Data obtained are consistent with what one would ex- sition. Moreover, and this is particularly important for pect for the material at hand, suggesting that the tech- fracture toughness tests, FIB milled straight-through nique is reliable despite the small specimen size, and notches always have a finite tip radius. These features that it can therefore be transposed to other materials. have been documented to potentially cause errors in Advantages of the method are that the obtained tough- fracture toughness measurements at the microscale. ness values are not affected by the finite radius of a FIB To circumvent the main problems associated with milled notch since the instability is developed from a FIB-milled specimens used for fracture toughness real (sharp) crack. In addition, at the onset of unsta- testing, we explore the testing of microscopic chev- ble growth, the majority of the crack front is situated ron-notched cantilever beams. Two simple, brittle and away from the FIB-machined surface. Thus, the meas- isotropic model materials are used to probe the tech- urements should be minimally influenced by milling-in- nique; namely, nanocrystaline alumina with a grain duced defects. The influence of environment-assisted size ~65nm, and amorphous fused quartz. Microscop- slow crack growth on the test data, which are well ic chevron-notched cantilever beams of rectangular known to be operative with alumina and fused quartz cross-section are machined using standard FIB mill- in air, is also examined in terms of various specimen ing. The beams contain a thin triangular ligament (the geometries and shown to be negligible in the present chevron notch), which is placed near the beam end at tests; there lies a third advantage of the method. Micro-fracture testing of tungsten single crystals Christoph Bohnert1, Nicola Schmitt2, Sabine M. Weygand1, Ruth Schwaiger2, Oliver Kraft 2 1Karlsruhe University of Applied Sciences, Faculty of Mechanical Engineering and Mechatronics (MMT), Karlsruhe, Germany 2Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Eggenstein-Leopoldshafen, Germany To be able to use tungsten as a structural material in mense influence on the fracture toughness. However, power generation, the characterization of its mechani- these studies have been mainly carried out at the mac- cal properties, in particular with respect to fracture, is ro-scale. To gain insight into the mechanical response essential. Previous studies on polycrystalline tungsten of individual grains, an experimental programme with already showed that the microstructure has an im- small scale fracture specimens was set up. Since the 268 Talks Topic G 6: Fracture mechanics standard procedure for fracture toughness testing is described by using a cohesive zone model (CZM). A not valid on this size scale, the experimental studies distinction between brittle or ductile fracture can be were closely accompanied by finite element simula- realized with parameter variations of the constitutive tions. traction separation law [3]. The aim of the present work is to find a procedure The developed crack model was applied to simulate to determine the fracture toughness of such small microbending. The simulations of microbending allow non standard specimen. The tested free-standing mi- for evaluating the details of the fracture process. The cro-bending beams have a typical dimension of 30 µm results reveal details of the developing plastic zone in width and thickness and 160 µm in length. They and which slip systems are active as well as the current were fabricated by micro-electro-discharging machin- crack growth rate. Furthermore, the computed load ing followed by surface cleaning and notching by fo- displacement curves are compared to the measured cused ion beam. A Charpy notch was chosen as it leads one. By this comparison, it has been confirmed that to a more controlled crack initiation as the resistance this procedure is suitable to determine values for the against crack propagation increases with increasing fracture toughness from experimental force-displace- crack length. The single crystalline beams starting with ment curves for small-scale specimen. For the single an orientation of the {001}<100>-crack system along crystals investigated, the obtained values agree well the loading direction were loaded using a nanoindent- with the ones from macroscopic tests for the same er. crystal orientation. Related to this experimental program a finite ele- ment (FE) study was performed. The FE model of the References notched microbeam was created taking into account R.J. Asaro. Advances in Applied Mechanics 23 (1983), plastic deformation at the crack tip. Plastic deforma- 1–115. tion is implemented using a crystal plasticity (CP) ap- Y. Huang. Division of Applied Sciences, Harvard Uni- proach (formulated by [1] and written by [2]) which versity, Mech. Report No. 178, 1991. allows for specifying the crystal orientation. Further- Ingo Scheider. 2006. The Cohesive Model Foundations more, the fracture process with crack propagation is and Implementation. GKSS Research Centre Geestacht An Improved Micromechanical Method for Investigating the Statistical Strength of Poly-Silicon Membranes John Brückner1, Holger Pfaff2 , Alfons Dehé3, Sven Rzepka1 1 Fraunhofer ENAS, Chemnitz, Germany 2 Keysight Technologies, Frankfurt, Germany 3 Infineon Technologies AG, Munich, Germany Freestanding poly-silicon membranes are of increasing mining the failure stresses of individual membranes, importance for designing MEMS devices such as pres- based on the mechanical test data. In a subsequent sure sensors, microphones and gyroscopes. It is crucial step the tests are analyzed via a two-parameter Wei- to accurately determine the mechanical properties of bull approach to statistically evaluate the characteristic such membranes not only to access parameters for de- fracture strength. signing new devices but also for assuring proper per- The membranes tested in the given project had a formance and quality in service. Classically, microscop- thickness of only 330 nm over a diameter of 1 mm. ic tensile tests [1-3] or bulge tests [4] were conducted The necessity to apply minute forces while testing the to obtain Young’s modulus and strength of the mem- compliant membranes at quite large deflections with brane material. These methods however are prone to high precision proves to be challenging. Additionally artifacts due to crack initiation at edge defects (e.g. the need for statistical verification requires conduct- predefined notches in tensile specimens [3] or slits in ing multiple tests in a reasonable time frame. In the bulge test samples [4]). In search of a method more presented work a commercial nanoindenter has been sensitive to the membrane surface rather than spec- used to match the aforementioned requirements. imen geometries, a novel approach has been intro- Lately some methodological improvements have been duced more recently. By loading the center region of a implemented to maximize throughput by automation circumferentially clamped membrane with a spherical and improve accuracy by refining the data analysis to probe, the membrane is stretched all the way up to capture the experimental conditions most realistically. rupture while precisely recording the load-deflection Some of these approaches will be illustrated by recent data. Complementary FEA simulations allow for deter- data and explained in detail. 269 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 References Films”, in Journal Of Microelectromechanical Sys- [1] Sharpe, W. N., Yuan, B., Vaidyanathan, R. and tems, Vol. 14 No. 5, pp. 1178-1186, October, 2005. Edwards, R. L.: 1997, Measurements of Young’s [3] H. D. Espinosa, B. Peng, “A New Methodology modulus, Poisson’s ratio, and Tensile strength of to Investigate Fracture Toughness of Freestanding Polysilicon, IEEE The Tenth Annual International MEMS and Advanced Materials in Thin Film Form”, Workshop on Micro Electro Mechanical Systems. An in Journal Of Microelectromechanical Systems, Vol. Investigation of Micro Structures, Sensors, Actua- 14 No. 1, pp. 153-159, February, 2005. tors, Machines and Robots, pp. 424-429. [4] B. Merle, M. Göken, ” Fracture toughness of silicon [2] T. Tsuchiya et al, “Cross Comparison of Thin-Film nitride thin films of different thicknesses as meas- Tensile-Testing Methods Examined Using Sin- ured by bulge tests”, in Acta Materialia Volume 59, gle-Crystal Silicon, Polysilicon, Nickel and Titanium Issue 4, Pages 1772-1779, February, 2011. How Crystals Break – Crack speed dependent environmental effect and surface instabilities Anna Gleizer, Liron Ben-Bashat Bergman, Dov Sherman Dept. of Materials science and engineering, Technion, Haifa, Israel A common wisdom is that cracks in brittle crystals such m/sec where the cleavage energy is 3.5 J/m2 (Gleizer & as diamond, silicon, or sapphire need excessive energy Sherman 2014; Gleizer et al. 2014). For the (111) cleav- to initiate and ‘bursting’ at high speed. Atomistic based age plane, SCC at energy of 2.2 J/m2 takes place up to theoretical studies and atomistic simulations, con- the maximum measured speed of 1200 m/sec. firmed by fracture experiments, have been in accord The second phenomenon is micron scale surface ridg- with the common intuition of speed (V>2,000 m/sec es generated when a slow crack is propagating on the in silicon) and energy (G0>1.6 .2gs). Contrary, continu- (111)[11 2 ] cleavage system of silicon (Kermode et al. um mechanics based theory predicts that cracks can 2008) under bending. The ridges initiate at atomistic be slow and initiate at 2gs. Our high-resolution fracture scale jogs generated when the running crack interact experiments confirm the continuum mechanics theory. with individual dopants. The jogs generate pile-ups In this talk, we will introduce our experimental meth- that terminate at micron scale ridges Ben-Basat Berg- od. The method consists of gluing a rectangular and man & Sherman 2014); Kermode et al. 2013). thin precracked brittle crystal specimen inside a rec- tangular hole in an aluminum loading-frame by two References 300 mm thick epoxy resin layers. Crack initiation and Ben-Basat Bergman, L. & Sherman, D. (2014): Dynamic propagation takes place upon heating the assembly on crack surface instabilities initiated at dopants. Scrip- top of an electrical heating stage by few centigrade, ta Materialia 75, 14-17. sufficient to initiate and propagate a crack. A relatively Gleizer, A. & Sherman, D. (2014): The cleavage ener- long (>10 mm) precracks were introduced in the spec- gy at initiation of (110) silicon. Int. J. Fracture 187, imens (Sherman & Gleizer 2014; Gleizer & Sherman 1-14. 2014). The strain energy release rate, G0, was calcu- Gleizer, A., Peralta, G., Kermode, J. R., de-Vita, A. & lated by quasi-static finite element analysis, and crack Sherman, D. (2014): Dissociative chemisorptio of O2 speed evaluated by Wallner-lines technique. With this inducing stress corrosion cracking in silicon crystals. method, we are able to manipulate the energy flux Phys. Rev. Let. 112 115501. to the crack tip to be low, responsible for low speed Kermode, J.R., Albaret, T., Sherman, D., Bernstein, N., cracks. We will introduce two governing parameters, Gumbsch, P., Payne, M.C. , Cs´anyi, G . & De Vita, A. dG0/da and dV/da (a-the crack length), and the way to (2008) Low Speed Fracture Instabilities in a Brittle control them. Crystal. Nature 455 1224-1227. We will show two important phenomena associated Kermode, J . R . , Ben-Bashat Bergman, L . , Atrash, with low speed cracks in silicon crystal. The first is crack F. , Cilliers, J. J., Sherman, D. & de Vita, A. (2013): speed dependent stress corrosion cracking, or subcrit- Macroscopic scattering of cracks initiated at single ical crack growth, for cracks propagating on the (110) impurity atoms. Nature Communication 4, 2441. [1 1 0] low energy cleavage system of silicon and crack Sherman, D. & Gleizer, A. (2014): Evaluating the cleav- speed independent stress corrosion cracking on the age energy of brittle single crystals. Performance (111)[11 2 ] crack system. For the (110) plane, full SCC and Characterization. Mater. Perfor. and Charact. 3, occurs at cleavage energy of 2.2 J/m2 up to crack speed 1- 25. of ~500 m/sec, and terminates at crack speed of ~1200 270 Talks Topic G 7: Fracture mechanics Talks Topic G 7: Fracture mechanics 271 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Influences of hydrogen-affected yielding and work hardening on plastic zone evolution studied by Finite Element Method Daisuke Sasaki, Motomichi Koyama, Kenji Higashida, Kaneaki Tsuzaki, Hiroshi Noguchi Department of Mechanical Engineering, Faculty of Engineering, Kyushu University, Fukuoka, Japan Hydrogen uptake is well known to accelerate fatigue transition condition under hydrogen atmosphere. The crack propagation rate due to a change in a crack prop- solution of the remaining issue enables us to estimate agation mode, deteriorating fatigue life drastically. precisely the condition. From the view point of the propagation mode transi- We have focused on the influences of hydrogen-affect- tion of fatigue crack under hydrogen environment, for- ed plastic deformation and a comparison parameter mation of brittle striation through transgranular crack for solving the remaining issue of plastic zone size. Me- propagation has been reported in Fe-Si single crys- chanical factors dominating plastic zone evolution are talline and commercial polycrystalline ferritic steels. considered to be yield strength and work hardening Additionally, the crack path was independent of any coefficient. In particular, the influence of work hard- identical crystallographic planes. This brittle striation ening coefficient has never been introduced to simula- was explained in terms of micro-void formations and tion of the HELP phenomenon. Additionally, expanded their coalescence associated with hydrogen-enhanced plastic zone was observed when compared using the localized plasiticity (HELP). The proposed model could stress intensity factor KI in a previous study. Based on explain the brittle-like fractographic feature as well as the crack-propagation mode transition mechanism, we the acceleration of crack propagation rate. This mod- have compared the plastic zone size by using the new el has enabled us to estimate the transition condition parameter, crack-tip plastic strain. by simulation. The estimate has an important role on This study has shown that hydrogen-reduced work prediction of fatigue life under hydrogen environment. hardening coefficient and the crack-tip plastic strain In this study, the hydrogen effect on plastic deforma- play important roles on simulating localization in plas- tion and hydrogen distribution at the crack tip have tic zone near the crack tip. Namely, special emphasis been analyzed by finite element method (FEM), since of this study was placed on the dependence of yield the propagation mode transition noted in this study strength and work hardening coefficient in hydro- has required the FEM-scale analysis which would eluci- gen-affected plastic zone evolution clarified through date hydrogen-related factors with a scale ranging from FEM and the influence of the new parameter. 30.0 μm (plastic zone size on steels at KI = 40.0 MPa√m) to 150 mm (the distance where the displacement is not References affected by plastic zone at a crack tip): hydrogen distri- H. Nishikawa, Y. Oda, Y. Takahashi, H. Noguchi: J. Solid bution, plastic zone size, plastic strain distribution, and Mech. Mater. Eng., 5, (2011), 179. coordination state of hydrogen such as dislocations. P.J. Ferreira, I.M. Robertson, H.K. Birnbaum: Acta Ma- The FEM has been successfully applied to the plastic ter., 47, (1999), 2991. zone analysis with hydrogen diffusion near a crack tip. P. Sofronis, R.M. McMeeking: J. Mech. Phys. Solid., Here, we noticed a remaining issue in terms of the 37, (1989), 317. plastic zone analysis, namely, simulating hydrogen-lo- calized plastic zone which is needed to determine the 272 Talks Topic G 7: Fracture mechanics On the fracture toughness of fcc medium- and high-entropy alloys at ambient to cryogenic temperatures Bernd Gludovatz1, Keli V. S. Thurston1, Anton Hohenwarter2, Dhiraj Catoor3, Hao Bei3, Easo P. George3,4, Robert O. Ritchie1,5 1Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, CA, USA 2Montanuniversität Leoben, Department of Materials Physics, and Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben, Austria 3Oak Ridge National Laboratory, Materials Sciences and Technology Division, Oak Ridge, TN, USA 4University of Tennessee, Materials Sciences and Engineering Department, Knoxville, TN, USA 5University of California, Department of Materials Science and Engineering, Berkeley, CA, USA Medium- to high-entropy alloys are an intriguing new tions into deformation-induced nano-twinning at low- class of materials in which three, four, five, or more el- er temperatures. We also report initial results of the ements are present in equiatomic concentrations, with fatigue-crack propagation behavior of these materials the striking characteristic that they often crystallize as in the same temperature range. single-phase solid solutions with simple crystal struc- Research sponsored by the US Department of Ener- tures, despite containing high concentrations of multi- gy, Office of Science, Basic Energy Sciences, Materials ple elements with very different crystal structures. Al- Sciences and Engineering Division. though these alloys are interesting from a fundamental scientific viewpoint, they can have unusual mechani- References cal properties, which make them attractive for a wide Gali, A., and E.P. George. “Tensile Properties of High- range of applications. and Medium-Entropy Alloys.” Intermetallics 39 (Au- Here we examine equiatomic medium- and high-entro- gust 2013): 74–78. py, face-centered-cubic alloys, which exhibit a remark- Otto, F., A. Dlouhý, Ch. Somsen, H. Bei, G. Eggeler, and able combination of strengths above 1 GPa, tensile E. P. George. “The Influences of Temperature and ductilities of more than 50% and fracture toughness Microstructure on the Tensile Properties of a CoCrF- values exceeding 200 MPa√m at crack initiation and eMnNi High-Entropy Alloy.” Acta Materialia 61, no. more than 300 MPa√m (J > 500 kJ/m2) during stable 15 (September 2013): 5743–55. crack growth, properties which actually improve from Gludovatz, Bernd, Anton Hohenwarter, Dhiraj Catoor, ambient to cryogenic temperatures. This appears to Edwin H. Chang, Easo P. George, and Robert O. Rit- result from continuous steady strain hardening, which chie. “A Fracture-Resistant High-Entropy Alloy for acts to suppress instability, consistent with planar dis- Cryogenic Applications.” Science 345, no. 6201 (Sep- location slip at ambient temperatures which transi- tember 5, 2014): 1153–58. Stress corrosion cracking in sensitized austenitic stainless steel type 304 under tetrathionate solution environment Tomoyuki Fujii, Keiichiro Tohgo, Yutaro Miura, Yoshinobu Shimamura1 Department of Mechanical Engineering, Shizuoka University, Japan Stress corrosion cracking (SCC) is a degradation phe- processes from micro crack initiation to macro crack nomenon caused by specific combinations of stress, growth on a smooth surface based on stochastic prop- environment and material. In nuclear industries and erties for micro crack initiation and concepts in frac- chemical industries, much attention has been paid to ture mechanics for crack coalescence and growth. A SCC as a degradation phenomenon of materials and number of studies about crack initiation on the basis structures under corrosive environment. SCC life is of crystallographic investigation have been conducted. estimated by crack growth from the millimeter-sized Gertsman et al. measured misorientation of cracked crack detected in periodic inspection to final failure. grain boundaries of polycrystalline materials, and re- The process of micro crack formation is major part of ported that twin (S3) boundaries were immune to IG- SCC life. To predict SCC remaining life, it is necessary SCC. PAN et al. reported that general low-angle grain to consider SCC process of crack initiation. Tohgo et boundaries and S3 boundaries were immune to IGSCC al. developed a Monte Carlo simulation of the SCC in alloy X-750 but then some coincidence site lattice 273 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 (CSL) grain boundaries lying in the range S5- S49 were direction. The number of cracks and crack length in- found to be cracked. However, the influence of misori- crease with increasing loading time after incubation entation of grain boundary on IGSCC behavior remains period, and then, the number of cracks becomes con- to be clarified. stant. All cracks initiated in grain boundaries, and the In this study, to make clear micro crack initiation be- grain boundaries with the misorientation ranging from havior by SCC in sensitized austenitic stainless steel 20° to 60° seem to be susceptible to crack initiation. 304, a constant load tests was carried out under 1% tetrathionate solution environment. Before the tests, References the crystal orientation of specimen surface was meas- Tohgo K., Suzuki H., Shimamura Y., Nakayama G. & ured by a scanning electron microscope (SEM) with Hirano T.(2009); Monte Carlo simulation of stress an electrion back scattered deffraction (EBSD). Tensile corrosion cracking on a smooth surface of sensitized load corresponding to tensile strain of 1% or 2% was stainless steel type 304, Corrosi. Sci., 51, 9, 2208- applied under the corrosive environment, and then the 2217. applied load was fixed using compressive spring. Dur- Gersman V.Y. & Bruemmer S. M. (2001); Study of grain ing the test, the SCC behavior, such as crack initiation boundary character along intergranular stress corro- and growth, was observed by a video microscope every sion crack paths in austenitic alloys; Acta Materialia, five minites. After the tests, the crack length and num- 49: 1589-1598. ber of cracks were measured and the crack formation Pan Y., Adams B.L., Olson T. & Panayotou N. (1996); process was discussed. Grain-boundary structure effects on interglanular As a result of the in-situ observation, initiation of many stress corrosion cracking of alloy X-750; Acta Mater., cracks, crack coalescence and growth were observed. 44, 4685-4695. Most of the cracks are perpendicular to the loading Effect of post weld heat treatment on the long-term reliabili- ty of austenitic stainless steel 347H Jine-sung Jung, Han-sang Lee, Doo-soo Kim, Keun-bong Yoo Power Generatioin Lab., Research Institute of Korea Electric Power Corporation, Korea An austenitic stainless steel 347H is widely used in high in the material such as dislocation and planar fault act temperature components due to the excellent creep as favorable nucleation sites for precipitation [2]. strength and oxidation resistance. In the case of power Therefore, in order to decrease or prevent a weld- plants, the metal is used in heat exchanger as re-heat- ed joint of austenitic metals from relaxation cracking er and super-heater tubes. These tubes are joined by damage, there is a need to alleviate the residual stress welding for connecting each other. through the post weld heat treatment together with So, high residual stresses were existed on the welded an avoidance of grain boundary sensitization through a joints due to no post weld heat treatment for austenit- carbide formation on grain boundaries. ic materials following some codes. Consequently, po- In this study, the effect of PWHT on long-term reliabil- tential degradation on the joints could be preceded by ity of a welded boiler tube 347H was investigated. The high residual stresses during operation on a condition PWHT was conducted using a thermal pad at 900℃ for of high-temperature and –pressure. 2 hours. In these days, some failures on the welded joints of Prior to the long-term test, creep-rupture tests were austenitic 347H boiler tubes were happened in ther- performed on the condition of 650℃-176㎫ and mal power plants. There were some common features 600℃-265㎫. The time to rupture was significantly in- in the failures. Firstly, the cracks on the joints were creased upto four times as compared with the as-weld found at the heat affected zone within two years since condition. installation. Secondly, the hardness values were shown In order to apply a PWTH to a field, there is a need to near the HAZ as compared to the bare metal. Also, the checking the long-term effect on a weld joints of boil- cracks were propagated along the grain boundaries er tubes 347H. So both as-weld and PWHT tubes were showing the inter-granular fracture appearance. Ac- aged in a furnace at 600°C upto 1000 hours. And then cording to the previous studies, these phenomenons a series of hardness, high-temperature tensile and are assigned to the ‘relaxation cracking’ [1] or ‘reheat creep-rupture testsmechanical tests were conducted. cracking’ based on microstructure analysis. Also, high Also microstructure features such as dislocation densi- density of dislocations was observed on the HAZ using ty, precipitation fraction and size were analyzed using a transmission electron microscopy. Generally, defects SEM and TEM. 274 Talks Topic G 7: Fracture mechanics In the case of 100 hours aging, the ultimate tensile References strength (UTS) of the PWHT sample showed a similar H. van Wortel; Control of Relaxation Cracking in Aus- level with that of as-weld sample in a high-tempera- tenitic High Temperature Components; In: Proceed- ture tensile test, while the elongation was significantly ings of the NACE International Conference on Corro- increased. Also, the decrease of dislocation density in sion 2007, Paper No. 07423. the PWHT joint was observed. Dutta B, Valdes E, Sellars CM. Mechanism and Kinetics Consequently, the beneficial effect of PWHT on the of Strain Induced Precipitation of Nb(C,N) in Austen- weld joint during the short-term was clearly confirmed. ite, Acta Metall Mater, 1992, Vol. 40, pp.653-662. The long-term effect are focusing on an increase of ductility through the control of precipitation behavior. Interaction between torsion damage and toughness anisot- ropy in a drawn pearlitic steel wire Aurélie Jamoneau1, Jean-Hubert Schmitt1, Denis Solas2,3 1Ecole Centrale Paris, Laboratoire MSSMat, Châtenay-Malabry Cedex, France 2Univ Paris Sud, ICCMO, Orsay, France 3CNRS, Orsay, France Pearlitic steel wires drawn under large strains experi- stress level is high, delamination starts at the first ence a high strength hardening, a microstructure re- steps of the torsion.Comparisons between differ- finement, and a morphological anisotropy. The streng- ent initial load states lead to quantitative evalua- htening mecanisms in tension have been widely stud- tion of toughness. ied accounting for the fine structure of the pearlite • Inverse torsion can also reveal the surface defect and the arrangement of lamellae[1, 2]. The mechanical intensity. In fact, the main stress component ap- behavior is strongly dependent on the loading condi- plied on the wire surface in torsion is shear stress, tions: along the longitudinal direction, the maximum which contributes to crack opening in mode III. tensile strength is significantly high while the total However, at the beginning of the inverse torsion, elongation is low, whereas in torsion lower maximum due to the inclination of defects with respect to shear strength and high ductility are observed [3]. the torsion axis, tension applies normaly to the Moreover, a strong toughness anisotropy, linked to the defect plane. If the defect is deep enough aftre morphological texture [4], contributes to the devel- pre-torsion, this could activate longitudinal cracks opment of a specific damage mechanism and rupture opening in mode I. mode in torsion [5]. • Electropolishing after pre-torsion reduces the The present work focuses on the mechanical behavior depth of the initial defects. It is shown that it pre- of a drawn wire under sequential loadings, specifically vents delamination during inverse torsion. torsion followed by inverse torsion. Mechanical test- ing, SEM observation as well as X-Ray diffraction are These results have to be completed in order to obtain used to characterise the material from the macro to quantitative predictions of the rupture mechanisms as the nano scale. a function of drawing and pre-deformation in torsion. When the torque vs. angle curves present a smooth Further studies of the crystallographic texture of the behavior leading to a ductile flat rupture in torsion, wire as well as EBSD maps of the structure along the strong irregularities appear on the shear curve during cracks could help resolving this issue. inverse torsion after a given amount of torsion. These mechanical irregularities are linked to the propagation References of a delamination crack along the radial {001} cleavage [1] J.D. Embury and R.M. Fisher, Acta Met. 1966, planes of the wire. 14:147 First results allow to partly explain the different behav- [2] G. Langford, Metall. Trans. 1970, 1:465 iors in torsion and inverse torsion: [3] T. Zhao et Al., Materials design 2014, 59:397 [4] A. Hohenwarter et Al., Metal. Mater. Trans. 2011, • Circonferential residual stresses, resulting from 42A:1609 drawing, influence the damage initiation: when [5] B. Goes et Al., Eng. Fract. Mech. 1998, 60:255 275 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic H 1: Materials for fission and fusion 276 Talk Topic H 1: Materials for fission and fusion Effects of helium and irradiation damage on microstructure and mechanical properties of Fe base alloys for fusion appli- cations Richard Kurtz Pacific Northwest National Laboratory, Richland, Washington, USA The products of a fusion nuclear reaction are a He nu- ing and irradiation creep. Again He can play a role in cleus and a 14 MeV neutron. The neutrons carry most exacerbating these degradation mechanisms. Toward of the fusion energy that is ultimately dissipated in the the upper operating temperature regime the effects of materials, components and structures surrounding the displacment damage are not the primary concern, but plasma. About 10% of the incident neutron energy is He may significantly impact service life by promoting deposited in the first-wall, while the balance is trans- grain boundary creep cavitation. Consequently devel- ferred to the much larger volume blanket behind the opment and qualification of structural materials for fu- first-wall. The neutrons are slowed by nuclear collisions sion nuclear service requires knowledge of the effects and reactions as they penetrate the reactor structure. of neutron damage and He over the entire tempera- The energetic neutrons interact with the atoms of the ture range. structural materials in two ways. One involves trans- Reduced activation ferritic/martensitic (RAF/M) steels mutation or conversion of one chemical element into and nanostructured ferritic alloys (NFA) are attractive another. In Fe base alloys the transmutation reactions materials for first-wall/blanket structural applications of greatest concern introduce copious quantities of He in advanced plasma devices and future fusion power and H by end-of-life. The other mechanism involves plants. RAF/M steels are much more technologically elastic and inelastic scattering collisions that generate mature than other candidate low-activation structural a cascade of atoms displaced from their equilibrium materials such as vanadium alloys and silicon carbide lattice sites. The vast majority of the displaced atoms composites. While NFAs do not enjoy the same lev- recombine with a vacant site, but a small fraction do el of technological maturity as RAF/M steels this new not. The surviving vacancy and interstital defect clus- class of material offers possible significant advantages ters can lead to significant changes in mechanical and such as the potential for higher temperature operation physical properties. and perhaps much greater radiation tolerance. The Neutron irradiation at temperatures below about 35% precise operating temperature and neutron dose lim- of the absolute melting temperature results in accu- its for these materials remains to be fully established mulation of point defect clusters to high levels, which because neutron-induced displacement damage cou- causes the yield and tensile strength to increase and pled with transmutation produced helium can lead to ductility to decrease. The resistance to crack propaga- significant degradation of mechanical properties and tion is also reduced. The effects of displacment dam- dimensional instabilities over the entire range of oper- age saturates at reletively low neutron dose, but He can ating conditions. In this paper we highlight recent ex- cause increased levels of hardening and embrittlment periments and modeling to characterize the effects of beyond displacment damage alone. At intermediate ir- He and irradiation damage on RAF/M steels and NFAs radiation temperatures Fe base alloys are susceptible for fusion applications. to dimensional instabilities such as volumetric swell- New Material Developments for Applications in Fusion Reactors J.W.Coenen1, J.Engels1, S.Heuer1, A.Houben1, B.Jasper1, A.Litnovsky1, Th.Weber3, T.Wegener1, W. Biel1, T.Hoeschen2, F.Koch2, R.Neu2, J.Riesch 2, M.Rasinski1, B.Unterberg1, Ch.Linsmeier1 1Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, Germany 2Max-Planck-Institut für Plasmaphysik, Garching, Germany 3Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Werkstoffstruktur und -eigenschaf- ten, Germany Materials for application in extreme environments have many ways do fulfill a functional role as well. Materials to show advanced properties in most areas ranging for the first wall of a fusion reactor have to face unique from mechanical strength to thermal properties and in challenges in many of these areas. The main challenges 277 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 include wall lifetime, fuel management and safety of Developments joining W as PFM with the structural operation. For the lifetime of the wall material, con- material EUROFER are also ongoing. To mitigate the ef- siderations of thermal fatigue as well as transient heat fect of mismatch in the thermo-mechanical properties loading are crucial as typical 109 (30Hz) thermal events functionally graded materials (FGM) are considered during one year of operation are to be expected. Tung- and shall be benchmarked with common joining tech- sten (W) is the main candidate material for the first niques. wall of a fusion reactor as it is resilient against erosion, In addition the issue of tritium management is an issue shows the highest melting point of any available ma- for future devices. In order to prevent tritium loss and terial and show rather benign behavior under neutron radiological hazards it is important to suppress tritium irradiation. permeation through reactor walls [4]. The require- To overcome the brittleness issue when using W, a ments on barrier layers are high permeation reduction W-fiber enhanced W-composite material (Wf/W) in- factors, high thermal stability and corrosion resistiv- corporating extrinsic toughening mechanisms can be ity as well as similar thermal expansion coefficients used. The extrinsic toughening allows for a certain tol- compared to the substrate. In Juelich a new deuteri- erance towards cracking and damage in general. The um gas-driven permeation setup is used to investigate tension can be released at the crack tip and thus cracks the deuterium permeation through different ceramic can be stopped where brittle, unenhanced tungsten coatings on EUROFER97 for example Er2O3. Such oxide would fail immediately. First samples have been pro- layers significantly reduce the deuterium permeation duced, showing extrinsic toughening mechanisms sim- compared to bare EUROFER97 substrates [5]. ilar to ceramic materials [1]. Overcoming the brittle- For the development of components including plasma ness problem will also mitigate effects of operational facing materials, functional layers and cooling struc- embrittlement due to neutrons and high operational tures the issue of power exhaust needs to be consid- temperatures. A component based on Wf/W shall be ered. This might require replacing copper by steel to developed with both a chemical infiltration (CVI), uti- avoid irradiation induced deterioration, e.g. swelling lizing a newly installed CVI-setup as well as a powder [6]. Using interface materials such as oxides in compos- metallurgical path through hot-isostatic-pressing. Me- ites and as permeation barriers may also decrease the chanical qualification and subsequent testing will be thermal properties and worsen the activation behavior used for qualifying the material options. of the components [7]. Therefor all of the above men- A potential problem with the use of pure W in a fu- tioned issues have to be tackled through an integral sion reactor is the formation of radioactive and highly approach. volatile WO3 compounds and their potential release under accidental conditions. A loss-of-coolant accident References (LOCA) in a He-cooled reactor would lead to a temper- [1] Riesch, J. et al., Physica Scripta, PFMC-14, 2014 ature rise to 1400 K after ~10–30 days due to the nucle- [2] D. Maisonnier, et al. Conceptual Study of Com- ar decay heat of the in-vessel components [2]. A future mercial Fusion Power Plants, Final Report, EFDA-RP- application of binary or ternary tungsten-based alloys RE-5.0, 13 April 2005 in a fusion reactor appears feasible, since these com- [3] W. Eckstein et al., Atomic and Plasma-Material pounds can also be processed to thick protective coat- Interaction Data for Fusion, 7b, IAEA, Vienna, 2001. ings with reasonable thermal conductivity, e.g. by plas- pp. 76. ma spraying with subsequent densification. Enhanced [4] Levchuck et al , Journal of Nuclear Materials 442 sputter erosion during normal reactor operation is not (2013) S592–S596 a concern, since preferential sputtering of alloying el- [5] Chikada et al. Journal of Nuclear Materials 442 ements will lead to rapid depletion of the first atomic (2013) S592–S596 layers and leave a pure W-surface in contact with the [6] S. A. Fabritsiev, S. J. Zinkle and B. Singh J. Nucl. plasma [5]. W-Cr-Y with up to 80% of W content already Mat. (1996) shows 105-fold suppression of tungsten oxidation due [7] Forrest, R.; Handbook of Activation Data Calculat- to self passivation. Rigorous testing of oxidation behav- ed Using EASY-2007 EURATOM/UKAEA Fusion Asso- ior as well as mass production for candidate materials ciation, 2009 will be performed. 278 Talk Topic H 1: Materials for fission and fusion Functional graded tungsten/EUROFER coating systems for First Wall application D. D. Qu1,, W.W. Basuki1, J. Gibmeier1, R. Vassen2, J. Aktaa1 1Karlsruhe Institute of Technology, Institute for Applied Materials, Germany 2Forschungszentrum Jülich, Institute of Energy and Climate Research (IEK-1), Germany Reduced activation Ferritic/Martensitic (RAFM) steels, assuming proper behavior for the different materials. e.g. EUROFER are primary structural material candi- Thereby the potential of the FG interlayer in reducing dates for the First Wall of DEMO, a demonstration re- stresses and inelastic strains and hence improving life- actor towards future fusion power plants (Kohyama et time is demonstrated. Based on the simulation results al. 1996). The interaction between plasma and FW, es- samples are fabricated by VPS with three different FG pecially physical and chemical sputtering will limit the interlayers’ thicknesses. The samples are comprehen- FW lifetime under normal operation (Ehrlich 1999). sively characterized performing measurements of re- Therefore tungsten coating is selected to protect the sidual stresses on the surface and among global depth FW due to its very low sputtering yield and low acti- direction, microstructural investigations including vation. However, the mismatch in thermo-physical porosity et al., and micro and nano-indentation tests properties between tungsten and EUROFER can lead identifying basic properties of the different layers. to large residual thermal stresses and even failure. The The status of development will be reported presenting application of functional graded material (FGM) is con- and discussing the main results collected so far as well sidered to be a good solution for the thermal mismatch as future theoretical and experimental work planned problem (Weber & Aktaa 2011). The erosion protective for the qualification of the developed coatings for FW tungsten coatings with tungsten/EUROFER functional application. graded (FG) interlayers on EUROFER substrate will be developed and optimized. The coating as well as the FG References interlayer will be produced by Vacuum Plasma Spray- A. Kohyama, A. Hishinuma, D.S. Gelles, R.L. Klueh, W. ing (VPS) with parameters optimized by modelling and Dietz, K. Ehrlich, Journal of Nuclear Materials 233- evaluated by means of microstructural and microme- 237 (1996) 138- 147 chanical investigations. K. Ehrlich, Phil. Trans. R. Soc. Lond. A 357 (1999) 595- To predict optimal parameters of the coating system 623T. Weber, J. Aktaa, Fusion Engineering and De- non-linear finite element simulations are performed sign 86 (2011) 220–226 CuCrZr alloys reinforced by Tungsten as structural Divertor applications for DEMO Jan Hoffmann1, Steffen Antusch1 , Jens Reiser1, Michael Rieth1,Verena Widak1, Soeren Mueller2, Hohe Joerg3 1Karlsruhe Institute of Technology (KIT), Institute for Applied Materials, Germany 2TU Berlin, Forschnungszentrum Strangpressen, Germany 3Fraunhofer-Institut für Werkstoffmechnanik (IWM), Freiburg, Germany One of the crucial points for future fusion reactors like tion of tungsten particles. the DEMO powerplant are the high heat flux compo- The present study shows the effect of (a) tungsten nents of the divertor. Due to the excellent thermal con- parcticles, (b) tungsten fibers and (c) tungsten foils on ductivity, copper alloys are considered as a candidate the mechanical and microstructural properties of the material for these applications in the fusion energy CuCrZr. The focus of the work was the feasibility of in- production. While conventional copper alloys have a dustrial produciton for the composites in large quan- limited operating window due to the low mechanical tities. strength [Reiser, 2012], reinforcement strategies for The correct heat-treatment processes were experi- copper-based compsites may extend this [Commin, mentally evaluated to reach the desired mechanical 2013]. The already superior mechanical performance and microstructural properties of the CuCrZr base ma- of the precipitation hardened CuCrZr compared to con- terial. Material of the same specifications was gas-at- ventional alloys can be further improved by the addi- omized into fine powders and mixed with smaller tung- 279 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 sten powder to reach a homogeneous distribution of to a copper matrix. Effects of the production routes on the two materials. The materials were characterized the resulting microstructure are discussed. The possi- before and after pre-sintering. The Pre-sintering of the bilities for mass fabrication and large scale processing powder-mixtures was followed by a hot extrusion at TU of pipes by hot extrusion are also adressed. Berlin. The resulting products were rod of diameter of 15 mm with a lenght of more than 2000 mm. References Characterizations were performed by Charpy impact Reiser J, Rieth M., Optimization and limitations of and tensile tests. The microstructure was analyzed by known DEMO divertor concepts, Fus Eng Des 2012; scanning electron microscoscopy combined with EDS 87 and EBSD maps. Commin L. et al., Assessment of copper based ma- In this presentation the authors give an overview of the terials for the Water-Cooled Divertor concept of concepts of CuCrZr reiforcements by tungsten. These the DEMO European Fusion reactor, Conf Fus Eng concepts include particle and tungsten wire additions (SOFE) 2013 Lithium evaporation and redeposition experiments under high density linear plasma dumping X. Cao, W. Ou, Z. Cao, Y. Xia, W. Zhang, X. Xue, C. Wang, J. Wang, D. Yang, S. Chen, F. Gou Liquid Metals Research Group, Institute of Nuclear Science and Technology, Sichuan University, Chengdu, P. R. China With many feasibilities of withstanding high heat flux, shielding role from the incident heat flux dumping. absorbing impinging species, compatibility with back Meanwhile, a semi-empirical temperature-dependent wall and recovery of lithium surfaces continuously, the model has been developed to simulate lithium evapo- prospect of using liquid lithium as first wall or liquid ration physics based on several assumptions. The mod- divertor target plate has been the ongoing object [1-2]. el is consistent well with experimental measurement However, due to the high evaporation rate, low ioni- result, which indicates high redepositon existence in zation energy and splashing under the Lorentz forces the experiment, and the redeposition rate increases at ELMS activities contrasted with conventional solid with the applied discharge current. plasma-facing component (PFC) materials [3], the in- teractions of core plasma and a large amount of evap- References orated lithium, splashed lithium, redeposition-induced [1] S.V. Mirnov, V.A. Evtikhin, The tests of liquid met- self-sputtering atom would reduce the temperature als (Ga, Li) as plasma facing components in T-3M of core plasma, which may terminate the fusion igni- and T-11M tokamaks, Fusion Engineering and De- tion[4]. sign, 81 (2006) 113-119. Lithium evaporation and redeposition with capillary [2] R. Bastasz, J.A. Whaley, Surface composition of pore systems (CPS) have been measured in one cath- liquid metals and alloys, Fusion Engineering and ode linear plasma device. As a candidate plasma-facing Design, 72 (2004) 111-119. material, a lithium sample with 1.2 cm in diameter with [3] Deng B Q, Huang J H, Yan J C, et al. Study of the different layers of meshes was fixed on the target plate. effects of liquid lithium curtain as first wall on plas- Langmuir probe is used to monitor the lithium evapo- ma[J]. Journal of nuclear materials, 2003, 313: 630- ration process near the specimen surface with adjust- 635.. able plasma parameters of electron temperature rang- [4] R. Majeski, R. Kaita, M. Boaz, P. Efthimion, T. ing from 0.4 to 0.9 eV and electron density from 0.8 to Gray, B. Jones, D. Hoffman, H. Kugel, J. Menard, 3.2´ 1019 m-3. The line intensity of lithium line 670.78 T. Munsat, A. Post-Zwicker, J. Spaleta, G. Taylor, J. nm is detected by multi-channel optical emission spec- Timberlake, R. Woolley, L. Zakharov, M. Finkenthal, troscopy (OES). The experimental results show that a D. Stutman, G. Antar, R. Doerner, S. Luckhardt, R. reduction in lithium evaporation by a factor of 0.2–0.7 Seraydarian, R. Maingi, M. Maiorano, S. Smith, D. is found with increasing the layers of mesh, which is Rodgers, V. Soukhanovskii, Testing of liquid lithium relevant to the binding energy Ea increase with layers of limiters in CDX-U, Fusion Engineering and Design, 72 meshes. And the evaporated lithium vapor cloud plays (2004) 121-132. 280 Talks Topic H 2: Materials for fission and fusion Talks Topic H 2: Materials for fission and fusion 281 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Analyzing the ions radiation-induced defects and cavity swelling evolution in representative PWR internal austenitic steels Bertrand Michaut1, Joël Malaplate1, Alexandra Renault Laborne1, Faiza Sefta2, Daniel Brimbal3, Lionel Fournier3, Brigitte Décamps4 1CEA, DEN/DANS/DMN/SRMA/LA2M, 91191 Gif-sur-Yvette, France 2EDF R&D, MMC, Site des Renardières, Môret-sur-Loing, France 3AREVA NP, Paris La Défense, France 4CSNSM-IN2P3, Paris-Sud University, Orsay, France The French nuclear industry is looking into the exten- irradiations such as activation. Such experiments are sion of the operation time of pressurized water reac- performed to simulate PWR microstructural evolutions tors (PWR) up to 60 years. The nuclear reaction occurs under neutron irradiations. Two SA 304 and two CW in a vessel which contains the core internals supporting 316 both containing different amounts of carbon are the fuel assemblies. The lower parts of the internals investigated. are composed of Solution Annealed (SA) 304 austenitic The objective of this work is to study the microstruc- stainless steel plates and Cold Worked (CW) 316 stain- tural and microchemical modifications, induced by less steel bolts. Due to their high exposition to irradia- ion irradiation in PWR conditions and to determine if tion (< 10-7dpa/s) it is expected to reach doses as high swelling occurs or not. as 120 dpa after 60 years, at a temperature close to Characterization of the virgin materials is performed 300-370°C. (composition, grain size, dislocation network…). Irradi- Irradiation leads to microstructural and microchemi- ations at low (5 dpa) and moderate (40 dpa) doses with cal changes such as apparition of black dots, disloca- energetic iron ions (10 MeV, ~2x1012 ions.cm-2.s-1) tion loops, voids, bubbles, segregation and precipita- were carried out at JANNuS-Saclay facility (higher dose tion. These modifications may result in evolutions of – 100 dpa in the same conditions is also expected). To the macroscopic behavior (swelling, irradiation creep, counterbalance the flux effect, irradiation temperature hardening, and corrosion resistance). was set to 450°C. Radiation-induced microstructures Swelling is a macroscopic dimensional modification. are investigated by Transmission Electron Microscopy In Fast Breeder Reactors, it has been associated to (TEM). The evolution of radiation-induced defects as the formation and growth of cavities. It is a threshold cavities, Frank loops and precipitates with the dose are phenomenon which can be described by an incubation studied as well as the influence of carbon. period (void/bubble nucleation) followed by a macro- Among the results, observations on SA 304L show an scopic swelling (cavity growth). Recently bubbles have increase in the dislocation network. Faceted cavities been observed in PWR irradiated materials, but with- formed at low dose and do not grow from 5 to 40 dpa. out macroscopic swelling. With the aim of an extension Simultaneously a saturation of the faulted Frank loops of the operation time, the evolution of the microstruc- is already noticed at 5 dpa. Densities and sizes of frank ture at high doses is a matter of concern. loops and voids have been estimated, as well as micro- Heavy ion irradiations are a fast and relatively easy way scopic void swelling values. All results will be discussed to reach high doses and to avoid drawbacks of neutron with the literature. Insights in microstructure of austenitic ods steels Tim Graening, Michael Rieth, Anton Moeslang KIT, Institute for Applied Materials, Karslruhe, Germany Several years ago, the development of high perfor- terials under irradiation, which decreases lifespan of mance austenitic steels in Germany started with the structural materials dramatically. The solution to these goal to produce fuel rod cladding tubes for the appli- draw-back was to introduce nanoscale particles in the cation in fission power plants. The aim was to enhance surrounding matrix. They serve as traps for irradiation the oxidation, corrosion and creep resistance. Also induced vacancies which are produced by the collision some special phenomena such as swelling and irradi- cascade and reduce swelling due to irradiation. Hence, ation assisted stress corrosion cracking occur in ma- the mechanical properties can maintain over a long pe- 282 Talks Topic H 2: Materials for fission and fusion riod at high temperatures in hazardous environment. of powder with the help of TEM, SEM and XRD were [1–3] performed to make a comparison to the microstruc- Ferritic ods steels have been well researched in last ture of rods and hot-rolled sheets. In ferritic steels decades in contrast to austenitic steels in irradiated many studies about the nanostructure of Y have been environment, because of their enhanced swelling re- performed, to get a thorough understanding about the sistance and only use of low activation elements. Now- evolution of complex Y-Ti-O precipitates. We want to adays ods steels are also promising candidates for oth- acquire novel knowledge about the chemical structure er high temperature applications, for instance in solar of these clusters in each milling step and of the auste- power plants. Whereby the austenitic matrix has the nitic matrix. potential to sustain temperatures up to 700 °C and will Thus it is possible to bring the production of austenitic surpass the limit of 550 °C for recent ferritic ods steels. ods steel with a attritor mill to the next level up to in- [4] dustrial scale. To achieve homogenously distributed precipitates the process of mechanical alloying is essential and References followed by hot rolling or extrusion. To modify and [1] H. Oka, M. Watanabe, H. Kinoshita, T. Shibayama, affect the mechanical properties, it is important to N. Hashimoto, S. Ohnuki, S. Yamashita, S. Ohtsuka, J. acquire a thorough understanding of the evolution Nucl. Mater. 417 (2011) 279. of microstructure with respect to the production [2] K. Yabuuchi, Y. Kuribayashi, S. Nogami, R. Kasada, process. Therefore the investigation of powder in dif- A. Hasegawa, J. Nucl. Mater. 446 (2014) 142. ferent states and its influence on the properties of [3] A. Hirata, T. Fujita, Y.R. Wen, J.H. Schneibel, C.T. Liu, semi-finished products is inevitable knowledge to M.W. Chen, Nat. Mater. 10 (2011) 922. optimize the production process with an attritor mill. [4] P. Susila, D. Sturm, M. Heilmaier, B.S. Murty, V. Sub- Due to this background, studies about different states ramanya Sarma, J. Mater. Sci. 45 (2010) 4858. Studies of high dpa ion beam irradiation effects on fcc AA-6061 and fcc-bcc duplex steel 2205: micromechanical modelling and nano-indentation examination of hardness variations Michael Saleh1,2*, Paul Munroe2, Lyndon Edwards1 1 Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation. Kirrawee DC, NSW, Australia 2 School of Material Science and Engineering, University of NSW, Sydney, Australia The irradiation effects of high dpa and the ramifica- fail to induce the required damage. The main attribute tion on the engineering assessment of reactor com- of ion irradiation is the rapid accumulation of end of ponents in GEN IV systems is of considerable interest. life doses over a short duration.. Conversley, neutron Most polycrystalline metallic materials derive their irradiation experiments in thermal test reactors may strengths from the interactions of dislocations with de- accumulate damage at a rate of 3–5 dpa year, e.g. the fects such as solid solution alloying elements, intersti- ANSTO OPAL reactor with 20 MW is capable of 100 tial elements, other dislocations, grain boundaries and MeV with reactor face neutron thermal flux of 4.0E10 sub-microscopic precipitates. Irradiation of metals and n/cm2/s thus resulting in a less than optimal 2 dpa per alloys at temperatures below those that anneal their year. defects typically produces pronounced radiation hard- A key question still exits between the complemen- ening, this is investigated herein to better understand tarity of neutron and ion irradiation with respect to the application of complex alloys in future reactor sys- the nature of damage, size, density and distribution tems. . of dislocation loops; black dots; and the extent of the The current study focuses on ion beam irradiation of dislocation networks. Although the same number of AA6061 and Duplex steel 2205, utilising the ANATRES displacements can be produced using ion irradiation, Accelerator at ANSTO with 12 MeV Au+5 ions used as there are differences in spatial defect distribution be- the irradiating ions. To induce a 100 dpa damage, often tween thes e teh two. The post-irradiation measure- cited as the operating level of GEN IV reactor, heavy ments in effect quantify the final state of damage and Au+5 ions are necessary as self-ion irradiation would the neutron-ion equivalence without an evaluation of 283 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 the damage path. dividual grains within a multiphase alloy. The results The simulation code Stopping and Range of Ions in Ma- show a marked increase in the hardening of AA 6061 terials (SRIM) is used to model the irradiation process with a more modest increase in the Duplex steel 2205. and compute the initial required experimental flux. Coupling these results to micromechanical FEA and Post irradiation studies of the micromechanical behav- crystal plasticity modelling, the authors hope to better iour are done through nano-indentation (to a depth describe the role of multi-scale modelling in comple- of 300 nm) using a diamond Berkovich tip. This allows menting micromechanical testing and the extrapola- for estimates of moduli and relative estimates of the tion of results for engineering assessment. strengths and hardening of individual phases and in- Mechanical Behavior of Unalloyed Plutonium Adam Farrow, Tarik Saleh, Deniece Korzekwa, Jeremy Mitchell Nuclear Materials Science, Los Alamos National Laboratory, USA Plutonium possesses six solid allotropes between room (monoclinic), and gamma (orthorhomic) plutonium temperature and its melting point at 640 Centigrade, will be presented at different temperatures and strain displaying many unusual behaviors. The least dense rates, along with a brief review of the literature per- phase (~15.9 g/cc) is a face-centered cubic, which also taining to the complex deformation behaviors of vari- displays negative thermal expansion. The highest den- ous phases of unalloyed plutonium. sity phase (~19.9g/cc) is a simple monoclinic. As plutonium is extremely sensitive to processing his- The mechanical behavior of plutonium is widely varied tory and microstructure, these will be discussed in the throughout these phases, displaying a broad range of current work, with particular attention paid to bulk behaviors, many of which are linked to the theoreti- densities, microcracking issues during casting, and the cal melting temperatures of different allotropes. The effects of retained phases on the measurements of majority of phases only exist at temperatures above density and other parameters. Thermal expansion will half of their homologous temperatures, as calculated also be discussed in reference to material processing against the theoretical melting temperatures for each and testing and as a indication of preferred orienta- phase (Nelson, 1965). This leads to unusual behaviors tion in the specimen stock produced in support of this such as the observation that the beta phase, possess- study. ing a monoclinic unit cell of 34 atoms, can be pulled to 600% elongation. References Use of a videoextensometer and backlight in the plu- Nelson, RD, Bierlien, TK, and Bowman, FE (1965): The tonium facility at Los Alamos National Laboratory has Steady-State Creep of High-Purity Plutonium. Tech- resulted in new data sets with improved strain meas- nical Report BNWL-32, UC-25, Metals, Ceramics and urements over existing data sets. New results on the Materials, Pacific Northwest National Laboratory, compressive behaviors of alpha (monoclinic), beta Richland, WA, January 1965. Temperature dependent X-ray adsorption spectroscopy stud- ies of Fe, Cr, and Ni local atomic structure for ferritic and austenitic ODS steels Andris Anspoks1, Juris Purāns1, Aleksejs Kuzmins1, Pavel Vladimirov2, Tim Gräning2, Jan Hoff- mann2, Kārlis Lazdiņš1, Arturs Cintiņš1, Anton Möslang2, Michael Rieth2 1EXAFS Spectroscopy Laboratory, Institute of Solid State Physics University of Latvia, Riga, Latvia 2Institute for Applied Materials-Applied Materials Physics, Karlsruhe Institute of Technology, Germany Oxide dispersion strengthened (ODS) steels have ex- potential for use as structural materials for concentrat- ceptional thermal conductivity and low thermal expan- ed solar power plants, jet engines, chemical reactors sion demonstrating high-temperature creep, corrosion as well as for hydrogen production from thermolysis and irradiation resistance. Therefore, they have a great of water. Previous developments are focused mainly 284 Talks Topic H 2: Materials for fission and fusion on the nanostructured ferritic (Fe-Cr alloys) ODS steels Using our recently developed method combining re- with very promising applications in, e.g., fusion power verse Monte-Carlo and evolutional algorithms for EX- reactors up to about 650 oC [1]. AFS spectra analysis (RMC/EA-EXAFS) [2] we recon- Researchers from Karlsruhe Institute of Technology structed local structure of Y in Y2O3 and Y containing (KIT) suggested recently to employ the outstanding nanoparticles in ODS steels. perspectives of austenitic (Fe-Cr-Ni alloys) ODS steels We applied our methodology combining classical mo- for high temperature fusion applications and solar lecular dynamics with ab ignition EXAFS calculations power plants. It is expected that dispersion of nanos- (MD-EXAFS) [3] to validate existing MD models for Y2O3. caled oxides particles with still unknown structure (x) Samples were prepared by Karlsruhe Institute of Tech- Y2O3-(1-x)Ti(Fe)O2 will suppress the gas bubble growth nology, and XAS analysis was performed by Institute of and related void swelling under neutron irradiation and Solid State Physics. should reduce irradiation hardening, and increase high XAS has proved to be excellent tool for atomic struc- temperature resistance up to 800 oC. Moreover, auste- ture analysis. nitic steels are non-magnetic and do not suffer from a ductile-brittle-transition, which are typical drawbacks References of ferritic-martensitic steels. [1] Baluc, N., Boutard, J.L., Dudarev, S.L. , Rieth, M., We used X-ray absorption near edge structure (XANES) Brito Correia, J., Fournier, B., Henry, J., Legendre, F., and extended X-ray absorption fine structure (EXAFS) Leguey, T., Lewandowska, M., Lindau, R., Marquis, spectra to reveal phase and local structure of the ab- E., Muсoz, A., Radiguet, B., Oksiuta, Z. (2011) Re- sorbing atoms. These analysis revealed the phase and view on the EFDA work programme on nano-struc- local structure evolution of the Ti and Y in ODS steel tured ODS RAF steels, J. Nucl. Mater. 417: 149-153. matrix during mechanical alloying and thermal treat- [2] Timoshenko, J., Kuzmin, A., Purans, J. (2014) EX- ment. AFS study of hydrogen intercalation into ReO3 using We found that the increase of the milling time to 80 h the evolutionary algorithm. J. Phys.: Condens. Mat- reduces the crystallinity of the sample with a transition ter 26: 055401. point between 20 h and 40 h from bcc to fcc phase. [3] Kuzmin, A., Evarestov, R.A. (2009) Quantum We can clearly distinguish Ti and Y atoms in metallic mechanics-molecular dynamics approach to the and oxide states. XAS proved to be excellent tool for interpretation of X-ray absorption spectra. J. Phys.: answering question – when and how oxide nanoparti- Condens. Matter 21: 055401. cles are formed? 285 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic H 3: Materials for fission and fusion 286 Talks Topic H 3: Materials for fission and fusion Mechancial Properties of a PM2000 ODS alloy tested at tem- peratures up to 700°C Ude D. Hangen1, Asta Richter2 1Hysitron, Inc., Aachen, Germany 2Asta Richter, Technische Hochschule Wildau, Germany Mechanical materials properties at elevated temper- ical for the ODS strengthening mechanism. At 500°C up atures are of general interest because temperature to 700°C an increase in the creep strain rate is found plays a key role in the making and forming of materials. with a stress exponent of n=8.2. When returning to For materials used in hot environments the long term room temperature the mechanical behavior found be- stability of these properties plays an important role. In fore the heating experiment can be reproduced show- the recent years nanoindentation has become a tech- ing that the microstructure remains mostly unchanged nique that enables for testing at high temperatures by the heating experiment. and is now reaching levels of 700°C and beyond. These These findings by nanoindentation will be discussed are relevant for many applications in tooling industry, – they are in good agreement with literature data ob- metal processing and for structural materials used at tained by tensile testing. elevated temperatures. In the present work a PM 2000 FeCrAl alloy with small References nanodisperse particles has been investigated for its C.-L. Chen, A. Richter, L.-T. Wu and Y.-M. Dong, Materi- hardness and modulus as well as for the indentation als Transactions, Vol. 54, (2013) 215-221. creep behavior up to 700°C. The methodology of in- D.G. Morris, M.A. Munoz-Morris, Acta Materialia 61 dentation and the considerations taken for the high (2013) 4636–4647. temperature testing will be discussed. The experiments J.H. Schneibel, M. Heilmaier, W. Blum, G. Hasemann, show that the ODS strengthening mechanism is found T. Shanmugasundaram, Acta Materialia 59 (2011) to work up to a temperature of 400°C resulting in low 1300–1308. creep rates and a stress exponent of n=80 which is typ- High temperature investigation of the fusion relevant mate- rial EUROFER by instrumented indentation Julian Bredl, Manuel Dany, Hans-Christian Schneider, Oliver Kraft Karlsruhe Institute of Technology, Institute for Applied Materials, Germany The prediction of the mechanical behavior of structural tensitic steel. It is characterized at elevated temper- materials assigned for future fusion application at their atures up to 500 °C for different heat treatments. A operating conditions is a very important part of the decreasing deformation resistance with an increasing current fusion research. In this regard, the instrument- temperature, a highly temperature depending hard- ed indentation is an effective method of characterizing ness and an almost constant Young´s modulus of the even small neutron-irradiated samples. The determi- material is observed. nation of material parameters e.g. hardness, Young´s Besides conventional testing, indentation tests with modulus and yield stress is possible by using the con- multiple loading-unloading cycles were performed at tinuous recording of the indentation depth and inden- elevated temperatures. The results of these multi-cy- tation force, and appropriate analysis procedures. clic tests can be used for determining material param- With the high-temperature indentation device, devel- eter based on a neural network method (Tyulyukovskiy oped at KIT, it is possible to test materials at tempera- & Huber 2006). For such analysis, however, the quality tures up to 650 °C under remote-handling conditions. of the load-depth-time data is crucial and small varia- Former investigations with a test temperature up to tions, e.g. related to fluctuations in the cooling system 500°C have shown the functionality of the device and of the device, have a strong impact on the results. Thus, the thermal stability of the heating system. (Bredl, it has turned out that further improvements on the sta- Dany, Schneider & Kraft 2014) bility of the measurements are required to make full The focus of the investigations of this study lies on the use of this powerful method. Additionally to the spher- material EUROFER, a reduced-activation ferritic-mar- ical indenter tests, measurments with Vickers tips are 287 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 carried out with the high temperature indentation de- In summary, the presented results can be considered vice. As indenter tip materials, diamond and sapphire as the final validation of the high temperature inden- are used for both tip shapes. The latter is used since tation device, which can thus be transferred to a Hot diamond will react with steels at temperatures of 400 Cell of the Fusion Material Laboratory. Hence, a secure to 500°C. However, sapphire is much more compliant and valid characterization of small volumes of irradiat- than diamond and the influence of the tip material can ed materials at elevated temperatures has been made be seen in differences in load-displacement-curves. An possible. improved understanding of the mechanical behavior of the tip materials and their influence on the indentation References procedure at high temperatures and high loads is an Bredl, J.; Dany, M.; Schneider, H.-C. & Kraft, O. (2014): important result of this study. Determination of RAFM steel properties at high Another important issue is to establish a routine for temperatures by instrumented indentation – In: frequent inspections of the indenter tip to ensure valid Conference SOFT 2014. results for every indentation test. This is discussed in Tyulyukovskiy, E. & Huber, N. (2006): Identification of this study with respect to the remote handled opera- viscoplastic material parameters from spherical in- tion of the device in a Hot Cell. dentation data: Part I. Neural networks – In: Journal of Materials Research 21 (3) 664-676. Study of irradiation creep based on nanomechanical lab-on- chip testing Pierre Lapouge1, Fabien Onimus1, Yves Bréchet2, Thomas Pardoen3, Jean-Pierre raskin4, Renaud Vayrette3-4 1 CEA, DEN, Service de Recherches Métallurgiques Appliquées, Gif-Sur-Yvette, France 2 INPG, Laboratoire de Science et Ingénierie des Matériaux et Procédés, St Martin D’Hères, France 3 UCL, Institute of Mechanics, Materials and Civil Engineering, Louvain-la-neuve, Belgique 4 UCL, Institute for Information and Communication Technologies, Electronics and Applied Mathematics, Lou- vain-la-neuve, Belgique Metals and alloys (stainless steels, zirconium alloys, In- of silicon nitride with strong internal stresses to pull conel alloys) used as structural materials in the nuclear the specimen layer and (iii) a sacrificial layer of silicon core of pressurized water reactor undergo irradiation dioxide to release the test structure from the underly- creep deformation (Morize and Baicry 1985, Rogerson ing substrate. The small thickness of the material be- 1988, Scholtz and Matera 2000). A good understanding low few hundreds nanometers allow full irradiation by of the mechanisms that control the deformation is es- heavy ions with a kinetic energy of a few hundreds keV. sential in order to predict the dimensional changes un- The equilibrium of the freestanding structure is de- der irradiation. At the macroscopic scale, many exper- termined by the intersection between the elastic be- imental data are available. However, the microscopic haviour of the silicon nitride and the mechanical be- mechanisms are still not yet fully understood (Onimus haviour of the specimen. Hence one test structure and Béchade 2012). gives one point in the tensile response of the speci- Many different mechanisms are proposed in the litera- men. By modifying the length of the actuator, different ture (Matthews and Finnis 1988), involving for instance points of equilibrium can be reached and the specimen dislocation climb under irradiation, but only few exper- response in tension can be evaluated. imental results have revealed which mechanism is the As a first step, test structures were irradiated to assess most likely to control deformation creep. New exper- the mechanical behaviour of the irradiated copper iments allowing the characterization of these various specimen. The as irradiated microstructure was also mechanisms are therefore needed. characterized after Focus Ion Beam milling. In this study, a novel approach based on lab-on-chip The results are compared with other results obtained thin freestanding test structures is evaluated. This on on a bulk OFHC copper. chip test method has been developed and optimized at Catholic University of Louvain but not yet used in the References context of irradiation studies (Gravier et al 2009, Cou- Coulombier M., Guisbiers G., M-S. Colla, Vayrette R., lombier et al. 2012). An elementary test structure is Raskin J-P. (2012), Rev. Sci. instrum., Vol 83(10), pp. composed of three main elements: (i) a thin specimen 105004. layer of the material of interest, (ii) an actuator layer Gravier S., Coulombier M., Safi A., Andre N., Boe A., 288 Talks Topic H 3: Materials for fission and fusion Raskin J-P., Pardoen T. (2009), Journal of MEMS 18 sium, ASTM STP 939, pp. 101-119 (3), pp 555-569R Onimus F., Béchade JL. (2012), Comprehensive Nucle- Matthews J.R., Finnis M.W. (1988), JNM 19 pp 257-285 ar Materials, Vol. 4, pp. 1-31 Morize P., Baicry J., Mardon J.P. (1985) Zirconium in Rogerson A. (1988), JNM 159, pp 43-61 the Nuclear Industry, Seventh International Sympo- Scholz R., Matera R. (2000), JNM 283-287 pp 414-417 Atom probe tomography of nanoscale precipitates in 13% Cr ODS steels with Ti variation S. Rogozhkin 1,2, N. Orlov 1,2, A. Aleev 1,2, A. Bogachev 1,2, A. Nikitin 1,2, A. Zaluzhnyi 1,2, R. Lindau 3, A. Möslang 3, P. Vladimirov 3 1 SSC RF Institute for Theoretical and Experimental Physics, Moscow, Russia 2 National Research Nuclear University “MEPhI”, Moscow, Russia 3 Karlsruhe Institute of Technology, Institute for Applied Materials – Applied Materials Physics, (IAM-AWP), Germany Oxide dispersion strengthened steels are promising (areas containing not only yttrium and oxygen but also materials for a variety of applications. First, they obey titanium and chromium). Moreover, concentration of superior creep resistance at high operational temper- titanium in clusters was found to be higher than that ature compared to ferritic-martensitic steels. These of yttrium, which indicates the importance of these materials also demonstrate an increased radiation re- elements in cluster formation. The analysis allowed to sistance. study matrix composition, size and number density of It is commonly assumed that excellent mechanical oxide clusters. It is showed that the number density of properties of ODS steels are directly related to the high clusters grows from ~ 1×1023 m-3 (for 0 wt.% Ti steel density of well-formed oxide particles (such as Y 24 -32O3, or steel) up to ~ 1.5×10 m (for 0.4 wt.% Ti steel) yet Y-Ti-O) (Klimenkov 2009). However, our previous APT the mean size of these clusters remains stable (about ~ study of EUROFER ODS (Aleev 2011) revealed even one 3 nm). There are considerable evidences showing an order of magnitude higher amount of nanometer size important role of titanium in fine cluster formation in clusters enriched by Y, O, V. The effect of these clus- 13.5%Cr ODS alloys. ters on the mechanical and irradiation resistance prop- erties of ODS steels and, especially, evolution of their References chemical composition under irradiation was not inves- Klimenkov, M. (2009): Klimenkov M., Lindau R., Mo- tigated in detail. slang A. New insights into the structure of ODS One of the current focus in development of ODS steels particles in the ODS-Eurofer alloy, Journal of Nuclear is set on higher chromium concentration (more than Materials, 386–388 (2009) 553–556. 12%) which originates from corrosion resistance de- Aleev, A. (2011): Aleev A.A., Iskandarov N.A., Klimenk- ficiency of ferritic steels and controlled substructure. ov M., Lindau R., Möslang A., Nikitin A.A., Rogozhkin Addition of Ti in range of 0 to 0.5% leads to better S.V., Vladimirov P. , Zaluzhnyi A.G., Investigation of mechanical properties increasing number density of oxide particles in unirradiated ODS Eurofer by tomo- precipitates and decreasing their sizes. In the work graphic atom probe, Journal of Nuclear Materials, presented a model 13.5% ODS steel (He 2012) with 409 (2011) 65–71. variation of titan concentration in range of 0 to 0.5% He, P. (2012): He P., Klimenkov M., Lindau R., Moslang was investigated by means of atom probe tomography A. Characterization of precipitates in nano struc- technique. Analysis of spatial distribution of alloying tured 14% Cr ODS alloys for fusion application, Jour- elements in the investigated volumes revealed Clusters nal of Nuclear Materials, 428 (2012) 131–138. 289 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Identification of Cr-Y-O Nano-Cluster in a 14Cr Oxide Disper- sion Strengthened Steel Xue Hu 1,2, Wei Yan 1, Wei Wang 1, Yiyin Shan 1, Ke Yang 1 1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China 2 University of Chinese Academy of Sciences, Beijing, China Oxide Dispersion Strengthened (ODS) steels are being References developed as the most promising structural material Degueldre, C., et al. (2005). “Characterisation of oxide for the next-generation nuclear energy systems in Ja- dispersion-strengthened steel by extended X-ray ab- pan, Europe, and the United States, due to its excellent sorption spectroscopy for its use under irradiation.” resistance to irradiation damage and high-temperature Computational Materials Science 33(1-3): 3-12. creep. Ehrlich, K. (2001). “Materials research towards a fu- In this work, the preparation processing and mi- sion reactor.” Fusion Engineering and Design 56-57: crostructure of the Cr-Y-O nano-cluster dispersion 71-82. strengthened steel were mainly studied. The prepa- Miller, M. K., et al. (2006). “Characterization of precip- ration processing of Cr-Y-O nanocluster ODS steel is itates in MA/ODS ferritic alloys.” Journal of Nuclear different from that of other ODS steels. The Cr and Y Materials 351(1-3): 261-268. pure metal powders were ball-milled for 4h firstly, and Odette, G. R., et al. (2008). “Recent Developments in then the mechanical alloying Cr-Y powders were added Irradiation-Resistant Steels.” Annual Review of Ma- in the base alloying powders, i.e. China Low Activation terials Research 38(1): 471-503. Martensitic (CLAM) steel powder. After long-term me- Hirata, A., et al. (2012). “Characterization of oxide na- chanical alloying (MA) and spark plasma sintering (SPS), noprecipitates in an oxide dispersion strengthened the mixed powders were sintered to block-shaped ODS 14YWT steel using aberration-corrected STEM.” Acta steel, with a high relative density of 98.8%. Materialia 60(16): 5686-5696. The microstructure of the Cr-Y-O nano-cluster ODS Hirata, A., et al. (2011). “Atomic structure of nanoclus- steel is full martensite structure with highly dispersed ters in oxide dispersion strengthened steels.” Nature nano-precipitates, including Y2O3 particles (with the Materials 10: 922-926. size of 20-30nm) and YCrO3 particles (with the size of Hu, X., et al. (2013). “Evolution of microstructure and 5-30nm). In addition, the orientation relationship be- changes of mechanical properties of CLAM steel tween YCrO3 and the steel matrix have also been inves- after long-term aging.” Materials Science and Engi- tigated, with the zone axis relationship of [110]BCC-Fe// neering: A 586: 253-258. [011]YCrO3. Huang, Q., et al. (2011). “Progress in development of CLAM steel and fabrication of small TBM in China.” Journal of Nuclear Materials 417(1-3): 85-88. Deuterium retention in reduced-activation ODS steels irradi- ated with 20 MeV W ions O.V. Ogorodnikova1,2*, K. Sugiyama2, Z. Zhou3, Yu. Gasparyan1, V. Efimov1 1 National Research Nuclear University “MEPHI”, Moscow, Russia 2 Max-Planck-Institut für Plasmaphysik, Garching, Germany 3 University of Science and Technology Beijing, China Ferritic/martensitic steels are one of the candidate ma- swelling. Oxide dispersion strengthening (ODS) by the terials for the vessel of the spallation target, and re- addition of Y2O3 particles has been successfully applied duced-activation ferritic/martensitic (RAFM) steels are to improve high-temperature strength of of RAFM’s. first priority materials of structure for fusion nuclear Dispersion of a high number density of nano-size yttria reactors. These systems are desired to operate at rel- particles is also effective to reduce radiation-induced atively high temperatures. RAFM steels (e.g. Eurofer) microstructural change. possess exceptional thermal conductivity and low ther- In the present work, RAMF’s steels including Eurofer mal expansion while being strongly resistant to void (9% of Cr) and ODS steels produced in China with dif- 290 Talks Topic H 3: Materials for fission and fusion ferent amount of Cr, namely, 9%, 12% and 16% were D. Therefore, the D concentration in damaged steels exposed to low energy (~20-200 eV per D) deuterium increases. No pronounced effect of Cr on the D re- plasma up to a fluence of 2x1025 D/m2 in the tem- tention at radiation-induced traps under exposure at perature range from 290 K to 700 K. The depth pro- room temperature was observed. The D concentration file of deuterium (D) in steels was measured up to 8 at radiation-induced defects in ODS and Eurofer steels µm depth by Nuclear Reaction Analysis (NRA) and the irradiated at room temperature is similar. Strong in- total retained amount of D in those materials was de- fluence of D ion energy on both the D retention and termined by thermal desorption spectroscopy (TDS). surface modification was observed. Lower D retention It was found that D retention in ODS steels is higher near the surface in the case of irradiation with 200 compared to Eurofer steel. The D retention in undam- eV D compared to 20 eV was found for both undam- aged ODS steels strongly depends on the Cr content: aged and damaged steels. Surface morphology alters minimum for 12%Cr and highest D retention for 16%Cr due to preferential sputtering of light elements. The D were found which can be associated with a change plasma exposure at high sample temperature of 700 from Ferritic/Martensitic to pure Ferritic structure. K results in more pronounced nano-structured surface High temperature tail was observed in TDS for ODS modification which can be connected with migration steels which was not observed for Eurofer. The pres- of precipitates at 700 K. No visible difference in the ence of this tail is, probably, connected with D bound surface modification for different RAMF steels and for with precipitates. pre-damaged samples was observed. Pre-irradiation with 20 MeV W ions produces radia- tion-induced defects which act as trapping sites for 291 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic H 4: Materials for fission and fusion 292 Talks Topic H 4: Materials for fission and fusion Combined effect of radiation damage and helium on the hardening and embrittlement of ferritic / martensitic steels Yong Dai, Kun Wang, Christiane Vieh, Vladimir Krsjak Laboratory for Nuclear Materials, Paul Scherrer Institut, Villigen, Switzerland Ferritic / martensitic (FM) steels have been widely neutron irradiation, induced by combined effect of ra- studied in various fission, fusion and spallation mate- diation damage and helium in different FM steels at rials R&D programs. The understanding of irradiation doses above about 10 dpa and helium concentrations – induced embrittlement effect has been one of most above about 700 appm. important research topics because it is well known that It is of essential importance to understand the me- the ductile-to-brittle transition temperature (DBTT) of chanical behaviors of FM steels irradiated above 10 FM steels can be greatly increased by irradiation even dpa and 700 appm He because of the additional hard- at a relatively low dose level of few dpa. Furthermore, ening and embrittlement observed. Great efforts have many observations also indicate that helium can great- been devoted to microstructural investigations includ- ly influence the DBTT shift. It is, therefore, important ing TEM observations, positron annihilation and atom to understand the combined embrittlement effect of probe tomography analyses to obtain rather complete radiation damage and helium for fusion and spallation information of irradiation-induced microstructural applications due to high helium production rate of FM changes, both visible and invisible on TEM. Two novel steels in fusion reactor and spallation target irradiation observations are: (1) Helium bubbles of 1-2 nm sizes environments. are weak obstacles with barrier strength of 0.1 – 0.15. In order to support the R&D of high power spallation The great additional hardening can be attributed to targets materials, irradiation experiments have been the high density, ~1024/m3 of helium bubbles. While performed in the targets of the Swiss spallation neu- sub-nanometer sizeed vacancy-helium clusters detect- tron source (SINQ) at the Paul Scherrer Institute (PSI) ed by positron annihilation spectrometry analysis are since 1998. In FM steels irradiated at SINQ under a even much weaker. (2) With the transition from ductile mixed spectrum of high energy protons and spallation fracture mode to brittle (intergranular and cleavage) neutrons, accompanied with relatively high radiation fracture mode, defect-free dislocation channels disap- damage rate up to 12 dpa per year, helium/dpa ratio peared, instead, mechanical twins (never observed in ranges from a few appm He per dpa to about 90 appm FM steels) were produced. The formation of mechan- He per dpa. Various mechanical tests such as tensile, ical twins should be associated with the additional 3-point bend, Charpy impact, small punch and hard- hardening. These findings will be described in detail ness tests have been applied to investigate the irradia- and the combined effect of radiation damage and he- tion effect on the mechanical properties of FM steels. lium on the deformation mechanism of FM steels will The important finding is the additional hardening and be discussed. embrittlement, compared with that induced by fission Mechanical Properties of Irradiated Ferritic/Martensitic Steels Tarik A. Saleh, Stuart A. Maloy, Tobias Romero, Matthew E. Quintana Los Alamos National Laboratory, Los Alamos, New Mexico, USA The US Department of Energy Fuel Cycle Research and condition at most irradiation temperatures, especially Development Campaign supports research into ex- temperatures below 400°C. tending the life of cladding material in high burn up, This talk will present the mechanical behavior of F/M fast spectrum reactor environments. Doses of up to steels from a number of irradiation experiments, con- 400 dpa and irradiation temperatures of 300-550°C are centrating on two alloys: HT-9 (nominal 12Cr, 1Mo expected. Ferritic/martensitic (F/M) steels are candi- steel) and T91 (nominal 9Cr, 1Mo steel). An overview dates for cladding and core materials under these con- of various irradiation experiments will be presented, ditions due to their excellent resistance to void swell- including from spallation environments (STIPIV, STIPV ing and their relatively good ductility in the irradiated and MEGAPIE irradiations), thermal neutron environ- 293 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 ments (the UCSB ATR-NSUF irradiation) and fast neu- conditions from a the aformentioned neutron irradi- tron environments (FFTF reactor). As well as informa- ations, ranging in dose from 6-20 dpa at irradiation tion on handling and testing materials at the Wing 9 temperatures ranging from 300-500°C, as well as some hotcells in the CMR facility at the Los Alamos National higher dose data out to 150 dpa from the FFTF reactor. Laboratory. Mechanical test data from different lots of HT9 materi- Comparison of HT9 and T91 will be made at similar al will be compared as well. Influence of neutron irradiation on precipitate microstruc- ture in EUROFER97 Christian Dethloff, Ermile Gaganidze, Jarir Aktaa KIT - Karlsruhe Institute of Technology, Institute for Applied Materials (IAM-WBM), Germany Utilization of fusion as a future energy source, besides Precipitate size distributions are determined in two other sophisticated technologies, demands high per- areas of both unirradiated and irradiated samples. By formance structural materials. Reduced activation fer- using EDX we show that the total precipitate size dis- ritic / martensitic (RAFM) steels like the European type tribution can be easily separated for M23C6 and MX by EUROFER97 are primary candidate materials for this two log-normal distributions. The mean diameter of purpose, and provide good irradiation resistance at precipitates grows for MX from 21.1 nm to 29.0 nm by temperatures above 350°C and low activation. Howev- 37% and for M23C6 from 82.0 nm to 100.0 nm by 22% er, low temperature neutron irradiation still causes de- after irradiation. Precipitate densities for M23C6 are at fect formation in the steel microstructure. As a serious about 5.7x1019 m-3 in 3 of 4 samples, while MX den- consequence mechanical properties are affected lead- sity varies between 2.4x1019 and 4.2x1019 m-3. Due to ing to hardening and low temperature embrittlement. irradiation induced precipitate growth the precipitate In this work the influence of neutron irradiation on the volume fraction is increased from 0.97% to 1.44% after precipitate microstructure of EUROFER97 is adressed 32 dpa. by performing transmission electron microscopy (TEM) An estimation of hardening caused by irradiation in- investigations. For this purpose unirradiated samples duced precipitate growth after 32 dpa is presented. are compared to specimens which were irradiated to Application of the dispersed barrier hardening model a damage dose of 32 displacements per atom (dpa) at shows that the effect of precipitate growth on hard- 330°C in the BOR-60 fast breeder reactor in Dimitro- ening is negligible when compared to other irradiation vgrad, Russia [Petersen 2002]. The preparation of TEM phenomena like dislocation loop or helium bubble / specimens out of undefromed parts of unirradiated void formation [Weiß 2012]. Nonetheless, an increase and irradiated impact specimens involved cutting of of the precipitate volume fraction leads to a shift of slices of 3x4x0.15 mm3 sizes, mechanical polishing and steel matrix elements which could affect hardening final thinning to electron transparency by electrolytic and embrittlement. Further investigations concerning polishing (solution of 20% sulfuric acid, 80% methanol) irradiation defects formation are in progress. [Dethloff 2014]. TEM investigations were performed at 200 kV with a high resolution FEI Tecnai G2 F20 micro- References scope located in the Hot Cells of Fusion Materials Lab- Dethloff, C. et al. (2014): Quantitative TEM analysis oratory at KIT. Scanning TEM (STEM) is used for a high of precipitation and grain boundary segregation in Z-contrast in combination with energy dispersive x-ray neutron irradiated EUROFER97 – Journal of Nuclear spectroscopy (EDX) for element analysis. Materials 454: 323-331. TEM investigations on both unirradiated and irradiat- Petersen, C. et al. (2002): The ARBOR irradiation pro- ed samples show two basic different precipitate types. ject – Journal of Nuclear Materials 307-311: 1655- Large, for the most part elongated precipitates are lo- 1659. cated mainly along grain or lath boundaries, while small Weiß, O. J. et al. (2012): Quantitative characterization spherical ones are distributed randomly in the matrix. of microstructural defects in up to 32 dpa neutron EDX analysis shows them to be M23C6 and mainly Ta irradiated EUROFER97 – Journal of Nuclear Materi- enriched MX carbonitrides, respectively. Detrimental als 426: 52-58. composition changes of precipitates due to irradiation as well as irradiation induced new precipitate types like Cr rich α’ are not detected. 294 Talks Topic H 4: Materials for fission and fusion Atomic scale investigation of phase decomposition of Fe-22%Cr during thermal aging and subsequent heavy ion irradiation O. Korcuganova1,2, A. Aleev1,2, S. Rogozhkin1,2 1 National research nuclear university «MEPhI», Moscow, Russia 2 SSC RF Institute for Theoretical and Experimental Physics, Moscow, Russia Understanding of damaging and degradation process- treated up to 1200 h at 500 °C and the samples aged es along with correlation between atom-scale altera- up to 50 and 200 hours were afterwards irradiated by tion and macroscopic properties of solid state materi- heavy Fe ions up to 1 dpa. It was shown that the for- als is of very importance being a key topic in modern mation of α’ phase as well as behavior of oversaturat- material science. One of the focuses in this field is ed solid solution defies the classical law of coalescence binary systems based on iron, namely Fe-Cr alloy (Du- theory of Lifshitz-Slezov and clusters behavior under darev 2009). Its phase diagram is still a field of ongoing irradiation depends on their sizes. debates, which originates from the affinity of iron and chromium and magnetic nature of both of them (Xiong References 2011). In case of Cr concentration higher than 10% de- Dudarev, S. (2009): The EU programme for modelling composition of solid solution occurs. radiation effects in fusion reactor materials: An This work is devoted to understanding of the kinetics overview of recent advances and future goals. – J. of such a process in a Fe-22%wt.Cr alloy by means of Nucl. Mater.,386–388:1-7. atom probe tomography. The latter was used to quan- Xiong, W. (2011): An improved thermodynamic mode- titatively describe the nucleation and growth process- ling of the Fe-Cr system down to zero kelvin coupled es at atomic scale as well as stability of formed phases with key experiments. – Calphad, 35: 3: 355–366. under cascade forming irradiation. Material was heat Comparison of mechanical properties between the HT9 and Gr.92 steel with various heat treatment conditions in a view- point of microstructure SangGyu Park, HyeongMin Heo, JunHwan Kim, SungHo Kim Korea Atomic Energy Research Institute, Korea A Sodium-cooled Fast Reactor (SFR) is a reactor oper- perimental studies, as well as from correlations with ated by high-energy neutrons that enables it to recycle detailed information on boundary characteristics, the the spent fuel from a conventional light water reactor. heat treatment effects between HT9 and Gr.92 steel Because of its superior dimensional stability against fast are discussed. neutron irradiation, Ferritic-martensitic steel (FMS) of To find the optimized heat treatment conditions of the 9Cr and 12Cr steels, such as HT9 and Gr.92 are prefera- HT9 and Gr.92 steel, it was normalized in a range of ble to utilize in the fuel cladding of an SFR in Korea. The 950°C to 1100°C for 30 minutes, and tempered in the objective of this study is to compare the effect of the range of 700°C to 800°C for 1 hour to change the mi- heat treatment process on the mechanical properties crostructures. A tension test was carried out in accor- of an HT9 and Gr.92 steel in the viewpoint of micro- dance with the ASTM E8 specification. The strain rate structure. Both HT9 and Gr.92 steel were normalized was 0.005/min, and tests were performed from room and tempered with various temperature settings and temperature to 650oC. the vickers hardness test and tensile test were carried The microstructure of the HT9 and Gr.92 showed typ- out to find the optimized heat treatment range. The ical tempered martensite structure. As the tempera- microstructures observations were conducted using ture of the normalizing increases, the sizes of the prior OM, and the grain boundary structures were observed austenite increase. The Vickers hardness was linearly by Electron Back-Scattered Diffraction (EBSD). Based decreased with an increasing tempering temperature on the mechanical properties obtained from the ex- and it show higher values with an increasing normal- 295 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 izing temperature. Similar tendency were observed in References yield strengths obtained from the room temperature [1] ] Y. I. Chang, Technical rationale for metal fuel in test results. Both the yield stress and ultimate tensile fast reactor, Nuclear Engineering and Technology, stress decreased with an increasing tempering tem- vol. 39, no.3, 2007. perature. However, In the case of the samples normal- [2] J. H. Kim, H. M. Heo, J. H. Baek, and S. H. Kim, Eval- ized at 950oC, the strengths tested at 650oC show linear uation of the Mechanical properties of a HT9 fuel behavior in spite of increasing tempering temperature. cladding tube for a Sodium-cooled fast reactor, Jour- The effective grain size were measured by EBSD with nal of the Korean Institute of Metal and Materials, considering the misorientations over 15o. Both the HT9 vo. 51, no. 25, 2013 and Gr.92 steel show significant decrease of effective [3] R. L. Klueh and A. T. Nelson, J. Nucl. Mater., grain size after 950oC normalizing condition. This could vol.371, no. 37, 2007 be explained the enhancement of high temperature strength in HT9 and Gr.92 steel, and these results will be quantitatively discussed with an EBSD analysis re- sults in detail. Creep rupture behavior of the China Low Activation Marten- sitic steel at 600oC Xue Hu 1,2, Lixin Huang3, Wei Yan 1, Wei Wang 1, Yiyin Shan 1, Ke Yang 1 1 Institute of Metal Research, Chinese Academy of Sciences,Shenyang, China 2 University of Chinese Academy of Sciences, Beijing, China 3 State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao, China Reduced Activation Ferritic/Martensitic (RAFM) steels References have been considered as candidate structural materi- Eggeler, G. (1989). “The effect of long-term creep on als for future fusion nuclear reactors. As the primary particle coarsening in tempered martensite ferritic candidate structural material for the Li-Pb blanket, the steels.” Acta Metallurgica 37(12): 3225-3234. China Low Activation Martensitic (CLAM) steel was de- Fernández, P., et al. (2005). “Creep strength of re- signed and developed in China. duced activation ferritic/martensitic steel Euro- In this work, the creep rupture behavior of the CLAM fer’97.” Fusion Engineering and Design 75–79(0): steel at 600oC was investigated under the load of 130, 1003-1008. 140, 150, 170 and 200MPa. It was worth noticing that Hald, J. and L. Korcakova (2003). “Precipitate Stability the creep-rupture life of CLAM steel under 130MPa in Creep Resistant Ferritic Steels-Experimental In- (about 7914h) is much longer than that under 140MPa vestigations and Modelling.” ISIJ International 43(3): (about 969h), although the load was only decreased by 420-427. 10MPa. This led to that the long-term creep-rupture Hu, X., et al. (2013). “Evolution of microstructure and life of CLAM steel under the load of 130Mpa was much changes of mechanical properties of CLAM steel longer than the extended extrapolation of short-term after long-term aging.” Materials Science and Engi- stress/creep-rupture life. The 130MPa seemed to in- neering: A 586: 253-258. dicate a kind of threshold stress at 600 oC, lower than Kimura, K., et al. (2009). “Long-term creep deforma- which, the creep-rupture life could be significantly tion property of modified 9Cr–1Mo steel.” Materials elongated. In addition, during long-term creep expo- Science and Engineering: A 510–511(0): 58-63. sure, the martensitic laths and the precipitate distribu- Klueh, R. L. (2008). “Reduced-activation steels: Future tion changed significantly. Especially, the Laves phase development for improved creep strength.” Journal precipitated on the grain boundaries or lath bounda- of Nuclear Materials 378(2): 159-166. ries. The potential mechanisms controlling the excel- Kostka, A., et al. (2007). “On the contribution of lent creep properties, the creep damage behavior and carbides and micrograin boundaries to the creep the microstructure degradation of the CLAM steel have strength of tempered martensite ferritic steels.” also been studied. Acta Materialia 55(2): 539-550. Lee, J. S., et al. (2006). “Causes of breakdown of creep strength in 9Cr–1.8W–0.5Mo–VNb steel.” Materials Science and Engineering: A 428(1–2): 270-275. 296 Talks Topic H 5: Materials for fission and fusion Talks Topic H 5: Materials for fission and fusion 297 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Positron annihilation research on ferrtic/martensitic steels irradiated under mixed spectrum of high energy protons and spallation neutrons Vladimir Krsjak, Yong Dai Paul Scherrer Institut, Villigen, Switzerland The investigation of the helium-filled nano-scale de- describes larger clusters with low helium content, fects, particularly for those invisible by TEM, in irra- which are considered to be eventually precursors for diated materials is a significant challenge for both helium bubbles. nuclear and material researchers. The behavior and With increasing irradiation dose and irradiation tem- thermal evolution of these defects have an intrinsic perature the helium-to-vacancy increases, which effect on the material performance under irradiation. reduce the positron mean lifetime. At about 10-12 A number of positron annihilation spectroscopy (PAS) dpa/100 appm He, corresponding to irradiation tem- experiments was performed recently on various steels perature ~150-170°C, a local minimum of positron irradiated in the SINQ (the Swiss spallation neutron mean-lifetime was observed in investigated F/M steels. source) targets at PSI to 5-20dpa at the correspond- At higher irradiation temperatures - up to 480°C, in- ing irradiation temperatures between 100 and 480°C. crease of positron mean-lifetime indicates the coars- New methodology based on internal positron source ening of vacancy clusters along the formation of small was developed in order to investigate a wide range of helium bubbles. The results also show, that the max- sample designs and providing more reliable bulk in- imum capability of small vacancy clusters to accom- formation. The internal positron source utilized in the modate the transmutation helium increases with the experiments is based on the 44Ti/44Sc isotope, which irradiation temperature, which is in a good agreement is a typical product of spallation reaction in Fe-based with the theoretical modeling data [1]. It seems that materials and, with the half-life of nearly 60years, a the process of accommodation of helium by existing convenient radioisotope source. or newly radiation-induced vacancy clusters plays an The positron lifetime spectra obtained on various fer- essential role in the formation and growing of helium ritic/martensitic (F/M) steels show two defect com- bubbles. ponents having a lifetime 190—250ps and 350-500ps respectively. According to published theoretical data, Reference the first component was attributed to small vacancy [1] R.E. Stoller, Yu. N. Osetsky, Journal of Nuclear Ma- clusters up to about 12 vacancies, having a high heli- terials 455 (2014) 258–262 um-to-vacancy ratio around 1. The later component Loss of strength and embrittlement of neutron irradiated be- ryllium V. Chakin, A. Moeslang Institute for Applied Materials, Karlsruhe Institute of Technology, Germany Beryllium is essential as reflector and moderator for ated beryllium occur. This degradation of mechanical material testing nuclear reactors (SM, BR2, etc.), as properties facilitates to formation and propagation of plasma facing material and neutron multiplier for fu- brittle cracks in beryllium (Chakin 2011). In the worst sion reactor designs (ITER, DEMO) (Poitevin 2014), and case, the neutron irradiation can lead to loss of integri- as reflector material for the recently approved Euro- ty of beryllium components what is essential for safety pean Spallation Source (ESS) in Sweden. In these ma- reason. chines, beryllium is subjected to neutron irradiation There is a set of results on dose dependence of me- resulting in degradation of physical-mechanical prop- chanical properties of beryllium samples irradiated erties. Under neutron irradiation, beryllium can be at temperatures of 343-873 K up to neutron fluences damaged in different degree depending on irradiation (0.04-1.4)·1023 cm-2 (E>0.1 MeV) in different materi- parameters (temperature, neutron spectrum and flux, al testing nuclear reactors. Analysis of the data was damage dose and helium accumulation). In particular, performed that allowed to determine the tempera- loss of strength and embrittlement of neutron-irradi- ture-dose intervals where irradiation damage of mi- 298 Talks Topic H 5: Materials for fission and fusion crostructure and, accordingly, degradation of mechan- tion on boundaries that leads to loss of strength and ical properties of beryllium samples were significantly embrittlement of the irradiated beryllium samples un- manifested. It was found that the brittle fracture of der mechanical tests. beryllium samples accompanied by loss of strength started at the lowest temperature of 343 K after irra- References diation up to neutron fluence of 0.04·1023 cm-2 (E>0.1 Y. Poitevin, I. Ricapito, M. Zmitko, F. Tavassoli, N. MeV). Increasing the irradiation temperature leads to Thomas, G. De Dinechin, Ph. Bucci, J. Rey, A. Ibarra, less degradation of beryllium mechanical properties. D. Panayotov, L. Giancarli, P. Calderoni, J. Galabert, J. Evolution of beryllium microstructure under neutron Vallory, A. Aiello: Progresses and challenges in sup- irradiation is discussed. The irradiation-induced heli- porting activities toward a license to operate Euro- um accumulation in beryllium takes place resulting in pean TBM systems in ITER. – In: Fusion Engineering formation of small helium-vacancy clusters, voids and and Design, Volume 89, Issues 7–8, October 2014: bubbles. These irradiation defects cause swelling. As 1113-1118. a rule, the beryllium material is produced by powder V. Chakin, R. Rolli, H.-C. Schneider, A. Moeslang, P. metallurgy methods such as hot extrusion, high isostat- Kurinskiy, W. Van Renterghem: Pores and cracks in ic pressing, etc. Therefore, the beryllium material has highly neutron irradiated beryllium. – In: Journal of weakened grain boundaries. Under irradiation, aniso- Nuclear Materials, Volume 416, Issues 1-2, 1 Sep- tropic swelling of grains results in brittle crack forma- tember 2011: 3-8. Modeling Hydrogen Ad- and Desorption on Beryllium-(0001)-Surface Christopher Stihl, Dmitry Bachurin, Pavel Vladimirov Karlsruhe Institute of Technology, Institute for Applied Materials - Applied Materials Physics (IAM-AWP), Germany The proposed application of beryllium in future fu- Our model is based on a set of ab initio total energies sion devices like ITER and DEMO (Vladimirov, P.V. et al. for numerous hydrogen adsorption patterns on the (2014)) as a neutron multiplier and plasma facing ma- beryllium (0001) surface and includes two non-equiv- terial entails the necessity to deal with the production alent hydrogen adsorption positions, the hcp and the of radioactive tritium as a result of transmutation pro- fcc hollow sites. A suitable cluster expansion enabling cesses. As tritium retention and release is substantially total system energy predictions both for low and high altered on whether beryllium is deformed severely by hydrogen coverages was found using the MIT Ab initio creep as in some blanket designs, it is crucial to acquire Phase Stability (MAPS) code. This expansion was used a thorough understanding of the mechanisms of tri- in our Monte Carlo code which is able to run Metrop- tium accumulation and release which is relevant for olis or kinetic Monte Carlo (kMC) simulations to model the evaluation of total tritium inventory. As a first step concurrent de- and adsorption processes. The hydro- we perform calculations using the VASP code for basal gen desorption, adsorption and surface diffusion pro- (0001) surface which is known to be the most energet- cesses implemented in the kMC code were first mod- ically favorable among other hexagonal close packed elled using VASP ab initio molecular dynamics runs. surfaces in beryllium. Significant interlayer distance In this work, we present the first results of the appli- relaxation of the outermost surface layers is observed cation of our multiscale model. Specifically, conditions in both pure and fully covered with hydrogen basal sur- necessary for the occurrence of adsorption and de- face. It is found that the presence of hydrogen on be- sorption processes, the equilibrium hydrogen coverag- ryllium surfaces leads to a noticeable reduction of sur- es, resulting from concurrent desorption, adsorption, face energy and sometime to surface reconstruction. and surface diffusion processes are discussed. Activation energy profile for hydrogen diffusion within the outermost surface layers is calculated. Adsorption References of hydrogen molecule is simulated with the help of ab Vladimirov, P.V. et al. (2014): Current Status of Be- initio molecular dynamics. ryllium Materials for Fusion Blanket Applications, Further we develop a multiscale modeling approach Fus. Sci. Tech. 66: 28-37 to hydrogen adsorption and desorption on beryllium Sanchez, J.M. et al. (1984): Generalized cluster de- surface consisting of (i) ab initio calculations of total scription of multicomponent systems, Physica A: energies for particular configurations of hydrogen on Statistical Mechanics and its Applications, 128: 334- the surface (ii) a suitable cluster expansion (Sanchez, 350 J.M. et al. 1984) which approximates the energies of van de Walle, A. & Ceder, G. 2002: Automating arbitrary configurations, and (iii) a kinetic Monte Car- first-principles phase diagram calculations, Journal lo method for dynamic simulations of adsorption and of Phase Equilibria, 23: 1054-9714 desorption. 299 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Dislocation microstructure evolution in tungsten due to indentation loading simulated by discrete dislocation dynamics Kinshuk Srivastava1, Daniel Weygand1, Peter Gumbsch1,2 1IAM-ZBS, Institut für Angewandte Materialien-Zuverlässigkeit von Bauteilen und Systemen, Karlsruher Institut für Technologie (KIT), Germany 2Fraunhofer IWM, Freiburg, Germany Tungsten, owing to its material properties is a prom- loading along the [-149] and [011] directions, the mi- ising candidate for plasma-facing materials in nuclear crostructure evolution under spherical indentation in fusion reactors. Therefore to understand the plasticity micrometer sized tungsten single crystals is examined. in irradiated samples, it is first necessary to understand The primary mechanism of dislocation multiplication in the evolution of plasticity based on the activated slip the sample is cross-slip which leads to generation of systems in single crystals. very large density of dislocations and accommodation Screw dislocations have a much lower mobility com- of the plastic strain-gradients under the indenter. The pared to mixed dislocations. Therefore they govern the simulated slip system activity can also be used to inter- plasticity in body-centered cubic metals. Screw disloca- pret the plasticity mechanisms in experiments. tions glide by the thermally-activated kink-pair mech- anism [1] which is controlled by a stress-dependent References activation enthalpy. This activation enthalpy not only 1.) Dorn E, Rajnak S. 1964. Nucleation of kink pairs depends on the resolved shear stresses but also on the and the peierls’ mechanism of plastic deformation. so-called non-Schmid stresses. Trans.AIME. 230: 1052–64 A computational framework for three-dimensional 2.) K. Srivastava, R. Gröger, D. Weygand, P. Gumbsch, discrete dislocation dynamics (DDD), incorporating at- Dislocation motion in tungsten: Atomistic Input to omistic simulation results on the activation enthalpy Discrete Dislocation Simulations, International Jour- of screw dislocations in tungsten is presented [2]. For nal of Plasticity 47 (2013) 126-142 Characterization and modelling of the mechanical behaviour of Nb3Sn Gilles Lenoir, Veronique Aubin Laboratoire MSSMat (UMR CNRS 8579), Ecole Centrale Paris, France Materials without electrical resistance and a perfect response to thermo-mechanical loading due to the expulsion of magnetic fields, so called superconduc- manufacturing process, the cabling process and dur- tors, are important in fusion reactor components (to- ing service. Furthermore, degradation of the electrical kamaks, stellarators), magnetic resonance imaging performance of the strands under cyclic loading was (MRI) and in electricity transport. The materials cur- observed [Bruzonne 2002]. rently used in high field magnets limit the intensity of In order to predict the electrical behaviour of the the produced magnetic field to 12 Tesla. The use of ni- strand, its accurate mechanical behaviour is necessary. obium-tin (Nb3Sn) is essential to surpass this limit [To- It will be done by the characterization and modelling desco 2011]. of superconducting strands under monotonous and The superconducting domain, defined by the critical cyclic loadings. Monotonous tensile tests with unload- temperature, the critical field and the critical current ings and cyclic tensile tests at various mean stresses density in the superconducting material, is also de- were used to identify the constitutive equation. The pendent on the applied strain [Ekin 1980]. Nb3Sn is a model will then be validated on more complex tests brittle material and beyond a certain deformation, the corresponding to the loadings to which the strands are damage of the strands prevents the crossing of the cur- subjected throughout the manufacturing process and rent [Miyoschi 2009]. Under this critical value of defor- usage. In a second step, observations and analyses will mation, some materials show a reversible limitation of be performed to understand the origins of the degra- the critical current. This dependency is well known for dation of the electrical performance. Nb3Sn strands [Nijhuis 2009], whereas the mechanical In this paper, the characterized mechanical behaviour response is not. In fact, mechanical-electrical couplings of Nb3Sn superconducting strands is presented in two require a corresponding knowledge of the strand’s parts. The first one is devoted to the mechanical re- 300 Talks Topic H 5: Materials for fission and fusion sponse of the strands under monotonous and cyclic In: Filamentary A15 Superconductors Plenum Press, loading. The second step is the analysis of their local New York, USA, 187-203. properties. These steps are required to build an accu- Miyoshi Y., van Lanen E. P. A., Dhallé M. M. J., Nijhuis rate model adapted to the complex structure of the A. (2009): Distinct voltage–current characteristics of superconducting composite. Nb3Sn strands with dispersed and collective crack distributions – In: Supercond. Sci. Technol., vol. 22 References no. 8. Bruzzone P., Fuchs A. M., Stepanov B., Vecsey G. Nijhuis A., Ilyin Y., Wessel S., Krooshoop E., Feng L., (2002): Performance evolution of Nb3Sn ca- Miyoshi Y. (2009): Summary of ITER TF Strand Test- ble-in-conduit conductors under cyclic load [for ing Under Axial Strain, Spatial Periodic Bending and Tokamaks] – In: Applied Superconductivity, IEEE Contact Stress – In: IEEE Transactions on Applied Transactions on 12, 516–519. Superconductivity 19, 1516–1520. Ekin J. W., Suenaga M., Clark M. (1980): Strain scal- Todesco E., Zimmermann F. (2011): The high energy ing law and the prediction of uniaxial and bending LHC – In: CERN Yellow Report, talk at the 2nd EuCard strain effects in multi-filamentary superconductors – meeting, Paris. Characterisation and modelling of nuclear graphite : from micrometres to metres Dong Liu1, Peter Heard1, Gillian Smith1, Branko Savija2 Erick Schelangen2, Peter Flewitt1 1Interface Analysis Centre, HH Wills Physics Laboratory, School of Physics, University of Bristol, UK 2Civil Engineering & Geoscienses, Delft University of Technology, NL Graphite is used in UK gas-cooled reactors as a mod- which modify the deformation and fracture character- erator, a reflector and a structural component. The istics of the material. These approaches have revealed, integrity of the graphite bricks making up the reactor for the first time, the significant change of mechani- core are of major importance for the safe operation cal properties, for example flexural strength, over the and shut-down of the reactor. Specifically, an a near- length-scale from a micrometre to tens of centimetres. ly isotropic (ratio of about 1.1) Gilsocarbon graphite A synthetic multi-scale model of the microstructure is is used in the operating advanced gas-cooled reactors input to a finite element model to predict properties (AGRs) in the UK and life extension is planned. Gilso- for various amounts of porosity at the tens of centim- carbon graphite is a multi-phased, polygranular mate- eter length-scale. It is emphasized that input parame- rial containing pitch, Gilsonite filler particles and pores ters to these computer models have to be undertaken and are produced by pressing or moulding. When load- at the appropriate length-scale to allow predictions ed in bending, non-linear deformation occurs prior to with required confidence. When the necessary input failure. No evidence of plasticity has been observed in parameters are included in the microstructure-based these graphites hence the deviation from linear-elas- multi-scale numerical model it is possible to describe tic behavior is attributed to localised micro-cracking the deformation, fracture strength and the stochastic (Moskovic et al 2013). It was found that the micro- features of the strength of the graphite. structure in the Gilsocarbon graphite has multi-scale physical and mechanical characteristics. There is also References mass loss due to radiolytic oxidation during exposure Liu, D., Nakhodchi, S., Heard, P.J., Flewitt, P. E. J. to the reactor environment. Therefore, understanding (2014): Small-Scale Approaches to Evaluate the the multi-scale mechanical properties and establish a Mechanical Properties of Quasi-Brittle Reactor full range of characterisation of the Gilsocarbon graph- Core Graphite,” Graphite Testing for Nuclear Appli- ite is essential to extrapolate the measured properties cations: The Significance of Test Specimen Volume to the metre-length bricks. and Geometry and the Statistical Significance of In the present work, the microstructure and mechan- Test Specimen Population, STP 1578, Nassia Tzele- ical properties of Gilsocarbon graphite have been pi and Mark Carroll, Eds., pp. 1-21, doi:10.1520/ characterised over a range of length-scales. A range STP157820130127, ASTM International, West Con- of small-scale mechanical testing approaches are shohocken, PA 2014. described including a novel in situ micro-cantilever Moskovic, R., Heard, P. J., Flewitt, P. E. J., Wootton, M. technique based in a dualbeam workstation (Liu et R. (2013): Overview of strength, crack propagation al 2014). It was found that pores ranging from nano- and fracture of nuclear reactor moderator graphite. metre to tens of micrometre in diameter are present Nuclear Engineering and Design. Vol 263, 431-442. 301 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic I 1: High temperature materials 302 Talks Topic I 1: High temperature materials Development of a novel microstructure highly resistant to grain boundary damage during creep at 950°C in Alloy 617 Ji-Won Lee1, Hyun-Hwa Park1,Tae-Ho Lee2, Hyun-Uk Hong1 1Department of Materials Science and Engineering, Changwon National University, Republic of Korea 2Department of Ferrous Alloy Research Group, Korea Institute of Materials Science, Korea The Ni-based superalloy Alloy 617 is considered as a the creep life could be extended to be 2.8 times longer primary candidate material for the intermediate heat as compared with standard specimen. The longitudinal exchanger (IHX) between the primary and the second- section of the standard specimen after creep rupture ary helium coolant circuits in the very high tempera- showed a typical sharp crack runningand propagating ture gas reactor (VHTR)[1]. The operation condition of along GB perpendicular to the loading axis in standard IHX requires the alloy to withstand mechanical deg- specimen. However, the serrated GBs (both serrated radation at 950 ˚C and 3~8 MPa in He impurities. The and pre-strained/serrated specimens) were highly re- reason of the requirement of the Alloy 617 as cadidate sistant to GB cracking, resulting in an isolated GB crack material for VHTR is due to its high-temperature me- with low frequency. It should be also noted that the chanical properties. Recently, however, there are some pre-strained/serrated specimen contained not only results that this alloy’s mechanical properties are un- coarsened primary carbides but also fine secondary stable during creep at very high temperature[1]. The carbides distributed uniformly in γ(FCC) matrix. The degradation of its properties resulted from the surface transmission electron microscopy indicated that the oxidation and decarburization along the grain bound- coarsened intragranular carbides without any interac- aries(GBs), the dissolution and redistribution of grain tion with dislocations in the standard specimen. It in- boundary(GB) carbides, GB migration and recrystalliza- dicated that initial fine carbides coarsened rapidly with tion. Hence, the great concerns could be given to the creep test. So, dislocation could slip well and reached to GB character for better performance of this superalloy. fracture in short time. In the case of the serrated spec- Therefore, in this paper, the heat-treatment for grain imen, there were a little intragranular carbides without boundary serration in Alloy 617 was introduced as any interaction with dislocations. However, this spec- one of the effective method to strenghthen the GBs. imen had the strengthened GBs, as the result, it had Actually, Hong et al. [2-4] conducted the specialized 2 tmes longer creep life. Finally in the pre-strained/ heat-treatment to induce the serrated GBs in Alloy 263 serrated specimen, the fine and stable carbides which and the serrated GBs enhanced creep properties due precipitated substantially through preliminary 5% cold to their low interfacial free energy. The proprietary di- work treatment, impeded effectively dislocation move- rect aging combined with controlled cooling rate led ment. Thus a correlation between metallurgical factors successfully to the transition of serrated GBs in Alloy and optimal microstructures has been proposed in ths 617. The lower final aging temperature produced high- work. er amplitude and higher fraction of serrated GBs. The micro structural observation revealed the serrated GBs References with stable planar M23C6 carbides and angulated MC [1] S. Kihara, J.B. Newkirk, A. Ohtomo, Y. Saiga, Metall. carbides in grain interior. After the creep test under Trans. A 11 (1980) 1019. 950°C/30MPa condition, the serrated specimen had [2] H.U. Hong, I.S. Kim, B.G. Choi, M.Y. Kim, C.Y. Jo, about 2 times longer creep life than standard speci- Mater. Sci. Eng. A 517 (2009) 125. men. Moreover, when the serrated specimen was sub- [3] H.U. Hong, H.W. Jeong, I.S. Kim, B.G. Choi, Y.S. Yoo, jected to 5% cold deformation before creep (referred C.Y. Jo, Phil. Mag. 92 (2012) 2809. to as ‘pre-strained/serrated specimen’, hereinafter), 303 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Numerical multi-criterion optimization method for develop- ing Ni-based superalloys: Development of a software tool and experimental validation Ralf Rettig1, NilsS C. Ritter1, Alexander Müller, Harald E. Helmer1, Robert F. Singer1 1Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute for Science and Technology of Metals, Erlangen, Germany Traditionally alloy development is still dominated by gle crystal alloy with nearly the same creep strength as extensive experimental research programs. However, the well-established rhenium-containing alloy CMSX-4 today sophisticated numerical tools are available for has been computationally developed. calculating many alloy properties in dependency of It has been found that the success of the optimization the composition. In this respect especially the CAL- is mostly related to the maximization of the concentra- PHAD-method shall be mentioned, which allows the tions of the solid solution strengthening elements (i.e. prediction of phase fractions and compositions of real- Re, W, Mo) in the g-matrix phase by optimization of istic alloys containing even ten elements or more (Ret- the partitioning ratio of those elements between g and tig et al. 2009). Further properties, for example density g’-phase. This is especially influenced by the g’-phase or γ/γ’-precipitate misfit are available via semi-empir- forming elements Al, Ta and Ti but also depends on the ical models. Despite this high potential, the true com- concentration of all other elements in the alloy. putational design of nickel-based superalloys is still in The approach and the actual optimization procedure the early stages (Egorov-Yegorov et al. 2005, Reed et as well as the verification of the calculations based al. 2009). This is mainly due to the many requirements on creep experiments and further property measure- for this class of alloys, for example certain γ’-phase ments of the cast optimum alloy are presented. fraction, misfit, low content of brittle TCP-phases, high creep strength and low density simultaneously. It is References not possible to maximize each of these properties and Rettig R., Heckl A., Neumeier S., Pyczak F., Göken M., therefore trade-offs, so called Pareto-optimum compo- Singer R.F. (2009): Verification of a commercial CAL- sitions have to be found. PHAD database for Re and Ru containing nickel-base In the present work, a new approach based on the superalloys. – Defect Diff. Forum, 289-292: 101-108. mathematical method of multi-criterion global opti- Egorov-Yegorov I.N., Dulikravich G.S. (2005): Chemical mization is presented which can easily manage the composition design of superalloys for maximum billions of potentially optimum alloy compositions. It stress, temperature, and and time-to-rupture using has been implemented with a deterministic Sequential self-adapting Response Surface optimization. – Ma- Quadratic Programming solver. In order to reduce cal- ter. Manufact. Proc., 20: 569-50 culation times, all properties were calculated from the Reed R.C., Tao T., Warnken N. (2009): Alloys-By-De- compositions via pre-calculated metamodels with the sign: Application to nickel-based single crystal su- Kriging-method. With this method a rhenium-free sin- peralloys. – Acta Mater., 57: 5898-5913. On the importance of the matrix for the creep properties of single crystal nickel based superalloys R. Völkl1, E. Fleischmann1, E. Affeldt2, U. Glatzel1 1Metals and Alloys, University Bayreuth, Germany 2Rabe MTU Aero Engines GmbH, Munich, Germany The creep properties of single crystal nickel based su- crostructural parameters. Due to the high strength of peralloys, consisting of a two phase g/g’-microstruc- the g’-particles creep deformation is strongly restricted ture, strongly depend on the size and volume content to the g-matrix. Thus the mechanical properties of the of the g’-phase and on the misfit between gamma and solid solution hardened matrix may become of high im- g’. They can be influenced by heat treatment or the portance. composition of the alloy. In the past a lot of work has In this study, nickel based superalloy single crystals with been done to determine the ideal values of these mi- different contents of matrix solid solution strengthen- 304 Talks Topic I 1: High temperature materials ers were cast, heat treated and creep tested at 980°C Reference and different stresses. The influence of the strength of Fleischmann, E. (2013): Einfluss der Mischkristallhär- the matrix on the creep properties of the superalloy as tung der Matrix auf die Kriechbeständigkeit einkris- well as the solid solution hardening efficiency of Re, W talliner Nickelbasis-Superlegierungen – Dissertation, and Mo in the matrix is determined. University Bayreuth 2013, ISBN 978-8440-2329-9. Influence of misfit stresses on dislocation glide in single crys- tal superalloys: A three-dimensional discrete dislocation dy- namics study Siwen Gao1, Marc Fivel2, Anxin Ma1, Alexander Hartmaier1 1Interdisciplinary Centre for Advanced Materials Simulation (ICAMS), Ruhr-Universität Bochum, Germany 2University Grenoble Alpes/CNRS, SIMaP-GPM2, Grenoble, France Ni-base (or Co-base) single crystal superalloys are fully taking into account internal misfit stresses. Misfit mainly applied as turbine blades in the hottest regions stress fields are calculated by the fast Fourier transfor- of gas turbines, due to their outstanding creep defor- mation (FFT) method and hybridized with DDD simu- mation resistance. In the characteristic g/g’ microstruc- lations. For external loading along the crystallographic ture of single crystal superalloys, the lattice mismatch [001] direction of the single crystal, it was found that of these two phases results in a significant misfit stress the different internal stress states for negative and field, which plays a decisive role for the micromechan- positive lattice mismatch result in non-uniform dislo- ical processes which lead to the observed macroscopic cation movement and different dislocation patterns in athermal deformation behavior of these high-temper- horizontal and vertical g matrix channels. Furthermore, ature alloys. The sign and magnitude of this lattice mis- positive lattice mismatch produces a lower deforma- match depend on the chemical composition of mate- tion rate than negative lattice mismatch under the rials as well as on the temperature. All currently used same tensile loading, but for an increasing magnitude Ni-base superalloys possess a negative lattice misfit of lattice mismatch, the deformation resistance always that becomes more negative with increasing temper- diminishes. Hence, the best deformation performance ature, while recently developed Co-base superalloys is expected to result from alloys with either small posi- with a similar g/g’ microstructure have a positive lat- tive, or even better, vanishing g/g’ lattice mismatch. tice mismatch that decreases at higher temperatures (Mughrabi, H. 2014). Reference Three-dimensional discrete dislocation dynamics (DDD) Mughrabi, H. 2014: The importance of sign and mag- simulations are applied to investigate dislocation glide nitude of g/g’ lattice misfit in superalloys---with spe- in g matrix channels and shearing of g’ precipitates by cial reference to the new g’-hardened cobalt-base superdislocations under external uniaxial stresses, by superalloys. Acta Mater., 81:21-29, 2014. TEM analysis of localized, planar deformation events which govern creep of single crystalline CoNi-super alloys with γ/ γ´-microstructures Yolita M. Eggeler 1, Julian Müller 1, Michael S. Titus 2, Akane Suzuki 3, Tresa M. Pollock 2, Erdmann Spiecker1 1 Center for Nanoanalysis and Electron Microscopy (CENEM), University of Erlangen-Nürnberg, Germany 2 Materials Department, University of California Santa Barbara, USA 3 GE Global Research Center, One Research Circle, Niskayuna, USA In the present study we use transmission electron peralloy with γ (fcc) - γ´ (L12) microstructure after [001] microscopy (TEM) to study the effect of creep on the tensile creep testing at stresses close to 300 MPa and a microstructures of a novel CoNi-based single crystal su- temperature of 900 °C. The alloy investigated contains 305 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 28 at.% Ni, which was added to the Co-Al-W ternary planes which are associated with a lower planar fault system to expand the γ-γ´ phase field and to increase energy. Further increase of the temperature results in the γ’-solvus temperature [1] . coarsening of the APB and lateral expansion of a disor- Conventional transmission electron microscopy (CTEM) dered (γ) region originating from the APB. Upon slow using two beam conditions with fundamental and su- cooling the γ’ phase nucleates in the form of small pre- perlattice reflections was performed for fault charac- cipitates at the position of the former APB. ChemiST- terization by applying the invisibility criterion. TEM EM reveals significant segregation at APBs corroborat- samples cut perpendicular to the tensile axis show a ing the importance of atomic diffusion and reordering high density of antiphase boundaries (APB) in the or- during creep, which can locally lower the planar fault dered γ’ precipitates produced by unit dislocations of energy. Furthermore, the in-situ TEM heating experi- type a/2[011] and a/2[01-1] which cut the γ´ phase ments confirm that tertiary γ’ precipitates do not act as [2]. Samples cut parallel to the tensile axis reveal the obstacles for dislocations at temperatures above 850 presence of extended ribbons of faults in the γ/γ’ mi- °C, and that the γ’ volume fraction decreases with in- crostructure. Along these defects, each γ’ precipitate cresing temperatures. exhibits a characteristic APB/SISF/APB configuration The present analysis contributes to a better under- whereby a superlattice intrinsic stacking fault (SISF) is standing of cutting events in CoNi-based Superalloys. fully embedded in an antiphase boundary (APB). While In particular, the importance of local diffusion, as ev- the SISF is confined to the (111) plane the surrounding ident from the APB migration, will be discussed, and APB shows migration towards energetically favorable the need for accurate predictions and assessments of {100} orientations. The two types of planar defects are fault energies and kinetics of the fault transformation separated by a Shockley partial dislocation loop with process will be emphasized. Burgers vector 1/6[-211] as explicitly shown by large angle convergent beam electron diffraction (LACBED). References Using CTEM, the translation vector of the APB was [1] K. Shinagawa, T. Omori, J. Sato, K. Oikawa, I. Ohnu- identified to be a/2[01-1], which is perpendicular to ma, R. Kainuma, and K. Ishida, “Phase Equilibria and the Burgers vector of the dislocation loop. The intrin- Microstructure on γ′ Phase in Co-Ni-Al-W System,” sic nature of the SISF was confirmed by high resolution Mater. Trans., vol. 49, no. 6, pp. 1474–1479, 2008. transmission electron microscopy (HRTEM) combined [2] Y. M. Eggeler, M. S. Titus, A. Suzuki, and T. M. Pol- with geometric phase analysis (GPA). lock, “Creep deformation-induced antiphase bound- Possible energetic and kinetic reasons for the nuclea- aries in L12-containing single-crystal cobalt-base tion of a SISF loop inside an APB and the relationship to superalloys,” Acta Mater., vol. 77, pp. 352–359, Sep. a similar mechanism in Ni-based superalloys [3] which 2014 has been controversially discussed in the literature are [3] M. Condat and B. Décamps, “Shearing of γ′ precip- addressed. itates by single a/2 〈110〉 matrix dislocations in a An in-situ TEM heating analysis of an APB originally ly- γ/γ′ Ni-based superalloy,” Scr. Metall., vol. 21, no. 5, ing on a {111} plane confirms the migration to {100} pp. 607–612, May 1987. 306 TalksTopic I 2: High temperature materials Talks Topic I 2: High temperature materials 307 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 On the Formation of Ledges and Grooves at γ/γ′ Interfaces of Single Crystal Superalloys Alireza B. Parsa1, Philip Wollgramm1, Hinrich Buck1, Aleksander Kostka1, Christoph Somsen1, An- tonin Dlouhy2, Gunther Eggeler1 1Institut für Werkstoffe, Ruhr-Universität Bochum, Germany 2Institute of Physics of Materials, Brno, Czech Republic Ni-base superalloys are material of choice for high that illustrates how stress filed of a dislocation changes temperature applications. Single crystal Ni-base super- the local chemical potential and provide driving force alloys are mainly used in gas turbine blades for energy for diffusional fluxes that result in the formation of a conversion and aero engines, where they are exposed groove. The results in this study hint that the forma- to elevated temperatures close to their melting point tion of grooves and ledges investigated represent an in a highly corrosive environment. The microstructure elementary process which, should be accounted for consists of two phases, γ and γ′, with coherent interface when rationalizing the kinetics of rafting i.e. the direc- where the γ′ cuboidal precipitates are in a γ matrix. In tional coarsening of γ′ cubes during high temperature this study formations of grooves and ledges have been deformation. investigated. Previous studies indicate that during high temperature low stress creep of Ni-base superalloys References the interface irregularities increase and show that their Kolbe M, Dlouhy A, Eggeler G. Mater Sci Eng A 1998; size and number increases. Diffraction contrast scan- 246:133. ning transmission electron microscopy (STEM) is used Epishin A, Link T, Nolze G. Journal of Microscopy 2007; as well as stereo microscopy to provide new evidence 228:110. for the existence of ledges and grooves. These features Link T, Epishin A, Paulisch M, May T. Mater Sci Eng A are usually accompanied with a dislocation nearby at 2011; 528:6225. the γ/γ′ interface. A small 2D model is implemented The influence of Re and Ru on the high-temperature creep strength and phase stability of Ni-based superalloys Kamil Matuszewski, Ralf Rettig, Robert F. Singer Institute of Science and Technology of Metals WTM, University of Erlangen-Nuremberg, Erlangen, Germany There is no doubt that the efficiency of gas turbines addition of Re from 1 to 2 at.% at the expense of Ni. is relying upon the temperature of the combustion Further, Ru raises the temperature limit by 38 K when process and, in turn, on the high temperature strength added to low Re-containing superalloys. of applied materials. Hence the increasing demand Besides the beneficial effect, the addition of Re results for more efficient stationary gas turbines for energy in a relatively strong dendritic segregation. This en- production drives the development in the field of Ni- forces firstly the need of expensive heat-treatments. based superalloys. Over the last decades the effort was Secondly, it leads to precipitation of topologically close succesfully put into the improvement of manufactur- packed (TCP) phases [7-9]. ing process, eventually leading to obtain single-crystal The effect of TCP phase precipitation is very detri- castings. Nowadays even more effort is put into the mental due to two main factors. At first, TCP phases optimization of the chemical composition of Ni-based are composed from refractory elements and thus they superalloys in respect to both high-temperature creep deplete the γ-matrix phase from strenghteners, i.e. strength and long-term phase stability maintaining rel- the solid solution strenghtening effect of expensive re- atively low costs of material. fractory elements cannot be fully used and thus creep The very high solid solution strengthening effect of Re strength is reduced [7, 8]. Secondly, TCP phases exhib- [1-3] and its very low diffusion coefficient [4, 5] bring it complex morphology, transforming with time from the significant improvement in high-temperature plate-like into lath-like particles [9]. Their precipitation strength. The previous results of our group [6] clear- can thus lead to a reduction of fatigue life-time of the ly indicate that the maximum application temperature material [8]. of Ni-based superalloys can be increased by 87 K with 308 TalksTopic I 2: High temperature materials In the present study we clarify the effect of Re and Ru References on the high-temperature phase stability of Ni-based A. F. Giamei, D.L. Anton, Met. Trans. A 16A, 1997-2005 superalloys in respect to predict their influence on (1985) high-temperature creep strength. G. L. Erickson, in Superalloys 1996 (The Minerals, Met- The microstructure of experimental Ni-based superal- als and Materials Warrendale, PA, USA, 1996), pp. loys with various content of Re and Ru is investigated 35-44 and studied quantitatively. The results show the huge D. Blavette, P. Caron, T. Khan, in Superalloys 1988 (The dependency of TCP phase precipitation on the Re-con- Metallurgical Society, Warrendale, PA, USA, 1988), tent. Influence of Ru is especially evident in the early pp. 305-314 stages of precipitation, i.e. nucleation. CALPHAD cal- M.S.A. Karunaratne, P. Carter, R.C. Reed, Mat. Sci. Eng. culations are performed to understand the information A281, 229-233 (2000) about Re and Ru influence. The results are comple- R.A. Hobbs, M.S.A Karunaratne, S. Tin, R.C. Reed, mented with the detailed chemical composition anal- C.M.F. Rae, Mat. Sci. Eng. A460-461, 587-594 (2007) ysis of TCP phases as well as γ/γ’ microstructure. It is A. Heckl, S. Neumeier, M. Göken, R.F. Singer, Mat. Sci. found that addition of Ru increases the solubility limit Eng. A528, 3435-3444 (2011) of Re within the γ-matrix phase. All this results togeth- R.A. Hobbs, L. Zhang, C.M.F. Rae, S. Tin, Met. Mat. er bring the new insight into the understanding the Trans. A 39A 1014-1025 (2008) effect of Re and Ru and optimizing the creep strength M. Simonetti, P. Caron, Mat. Sci. Eng. A254, 1-12 and phase stability of Ni-based superalloys. (1998) K. Matuszewski, R. Rettig, R.F. Singer, Proceedings of 2nd European Symposium on Superalloys and their Applications (Eurosuperalloys 2014), MATEC Web of conferences, 14 (09001), 1-6, (2014) Super-Solvus Heat Treatments of Ni-Based Superalloys in a Hot Isostatic Press/Quench Unit Lais Mujica Roncery, Inmaculada Lopez-Galilea, Benjamin Ruttert, Werner Theisen Chair of Materials Technology, Ruhr-Universität Bochum, Germany In the field superalloys, hot isostatic press have been rosity and microstructure of single crystal superalloys conventionally used to reduce the porosity generated [Lopez-Galilea]. In the frame of this work, the combi- during the cast and homogenization processes. The in- nation of different pressures and quench/cooling strat- tegration of the HIP within the steps conventional heat egies in a HIP/Quench unit is studied in the second treatment steps of casting à homogenization à pre- generation ERBO-1 (similar to CMSX-4) single crystal cipitation hardening has not a general rule. Some heat Ni-Based superalloy during super-solvus HIP treatment treatment schemes prefer the use of HIP after casting, (1280-1320°C). which is not useful since new pores can arise during From the process point of view, pressures between homogenization due to the Kirkendall effect [Bokstein]. 25 and 200 MPa are applied, having a direct influence Other schemes prefer the incorporation after homoge- on the physical properties of the gas such as density nization, nevertheless the use of a short annealing and and viscosity. Additionally, different nozzles are used quenching is additionally needed because of the limita- to influence de gas speed. The combination of these tions of most HIP units to incorporate quench. variables influences the heat transfer coefficient and New strategies in the development of the hot isostatic therefore the quenching speed. The extrapolation of press allow performing quenching during the HIP cycle. these factors for further integrated heat treatments is In such a way it is possible integrate heat treatments considered. within the HIP process [Åkerberg, Ahlfors, Laker]. In the From the microstructural point of view, the differences case of the superalloys, it is possible then to integrate of the relationship between the isostatic pressure and homogenization and HIP in one step, and even more the porosity of the material are analysed. Additional- to incorporate precipitation hardening within the HIP ly, the morphology of the g/g’ in dependence on the cycle. quenching rates are considered. Previous studies have shown the large influence of the cooling rate, temperature and pressure on the po- 309 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 References Control of Distortion Conference Bokstein B.S.,. Epishin, A.I , Link, T., Esin, V.A., Rodin Lopez-Galilea I.; Huth, S., Theisen, W. Fockenberg, T., A.O., Svetlov, I.L. (2007) Model for the porosity Chakraborty, S (2012) Effect of high pressure and growth in single-crystal nickel-base superalloys dur- high temperature on the microstructural evolution ing homogenization. Scripta Materialia 57 (2007) of a single crystal Ni-based superalloy. 801–804 Journal of Materials Science. Åkerberg, A. (2014). The difference between URQ and Lopez-Galilea, I. Huth, S. Theisen, W. (2014) Chal- U2RC. Proceedings of the 11th Conference on hot lenges in Reducing Casting Porosity in Superalloys. isostatic pressing. HIP’14 pp. 346–358 Ahlfors, M. (2014). The Possibilities and Advantages Lopez-Galilea, I., Huth, S., Theisen, W. (2014) Effect with Heat Treatments in HIP. Proceedings of the 11th of the cooling rate during heat treatment and hot Conference on hot isostatic pressing. isostatic pressing on the microstructure of a SX-Ni. Larker, R. Rubin, P. Uniform Rapid Quenching enables Superalloy. Proceedings of Eurosuperalloys. MATEC Austempering Heat Treatment in HIP (2012). Pro- Web of Conferences 14, 13009. ceedings from the 6th International Quenching and Crystal plasticity modeling of porosity reduction in an as-cast Ni-base single crystal superalloy during hot isostatic pressing Siwen Gao1, Inmaculada Lopez-Galilea2, Anxin Ma1, Stephan Huth2, Werner Theisen2, Alexander Hartmaier1 1Interdisciplinary Centre for Advanced Materials Simulation (ICAMS), Ruhr-Universität Bochum, Germany 2Institut für Werkstoffe, Ruhr-Universität Bochum, Germany Owing to the excellent performance of Ni-base single The temperature depency mainly comes from the at- crystal superalloys to resist extreme working condi- oms self-diffusion coefficients and the initial and satu- tions at high temperature, they are the material of rated dislocation slip resistances. choice for application in the hottest regions of mod- This study aims at determining the relationships be- ern gas turbine. Although the deformation resistence tween HIP parameters and pore annihilation kinetics. at the elevated temperature significantly increases by With respect to several quasi-2D pore geometries, we adding a high concentration of refractory elements, have achieved a good agreement between measrued a stronger dendritic segregation during solidification and simulated pore area reduction. It was found that and pores accumulation in the interdendritic region by increasing HIP temperature or by increasing isostat- during an extensive homogenization heat treatment ic pressure one can get compariable porosity evolu- tend to occur, which deteriorates mechanical proper- tions. We have also observed some important micro- ties of materials (Link, T. 2006). In order to heal these structure geometry influence such as: Under the same micropores, hot isostatic pressing (HIP) as an advanced conditions, large pore shrinkes faster than small one at thermal treatment is utilized, which combines creep the beginning; Big g’ phase paritcles near a pore retard deformation and diffusion bonding to homogenize the pore annihilation speed; Pore shape does strongly the alloy composition by the appropriate pressure and affect the pore shrinkage. high temperatures (Kim, M.T. 2006). According to the experimental observation of HIP on References an as-cast Ni-base single crystal superalloy, a qua- Link, T. 2006: Synchrotron tomography of porosity si-two-dimensional (2D) crystal plasticity finite ele- in single-crystal nickel-base superalloys. Materials ment model is developed to investigate the influence Science and Engineering A, 425:47-54, 2006. of different temperatures, isostatic pressures and dura- Kim, M.T. 2006: Effect of HIP process on the mi- tion time on the porosity reduction during HIP. In this cro-structural evolution of a nickel-based superalloy. crystal plasticity based creep model, the internal stress Materials Science and Engineering A, 441:126-134, caused by lattice misfit and strain heterogenity inside 2006. the typical g/g’ microstructure have been considered. 310 TalksTopic I 2: High temperature materials Characterization of <100> superdislocations and the γ/γ’ in- terface by an advanced FIB lamella lift out technique Julian Müller1, Michael J. Mills2, erdmann spiecker1 1 Center for Electron Microscopy and Nanoanalysis, University of Erlangen-Nürnberg, Erlangen, Germany 2 Center for Electron Microscopy and Analysis, Ohio State University, Columbus, USA Single crystalline Ni-based superalloys exhibit unique ingly, also the superpartials in which the superdisloca- properties when it comes to high temperature defor- tions dissociate do not experience glide or climb forces mation since they possess an excellent mechanical from the external load. Instead, an osmotic pressure stability, sufficient oxidation resistance and a good generated by a vacancy supersaturation is proposed to damage tolerance. As the complete deformation cause the dislocations to climb through the γ’ phase. mechanism from the as heat treated base alloy to the As a second application of the FIB lamella lift out tech- raptured creep sample is highly complex, there are still nique the γ/γ’ interface width is studied. Even though unresolved questions regarding the underlying micro- the preferential orientation of the interface is {100}, scopic mechanisms. Two key factors which influence locally it exhibits angular deviations of up to several the creep properties are the structure and local chem- degrees (~ 8° for the present sample). Consequently, in istry of the γ/γ’ interface and the cutting of the y’ a regular TEM sample it is not possible to ensure that phase by superdislocations. the γ/γ’ interface is in edge on orientation. As re- In the present work an advanced FIB lamella lift out sult projection effects lead to an overestimation of the technique is employed to study the above mentioned actual interface width. To overcome these limitations microstructural features of Ni-base superalloys. The a γ/γ’ interface region with in plane orientation very lift out technique is based on the preparation of FIB close to <100> was selected from a regular plan-view lamellas from conventional TEM samples. This enables TEM sample. The precise orientation of the interface characterizing e.g. a superdislocation first in plan-view was determined by means of selected area electron geometry by conventional TEM techniques and after- diffraction. Afterwards the FIB lamella lift out tech- wards in cross section geometry by HRSTEM to de- nique was employed to prepare a cross section sample termine the dislocation core configuration. Hence, it from the selected interface region. With this approach becomes possible to investigate a large number of dis- it was possible to reduce TEM projection effects to a locations in plan-view and categorize them in terms of minimum. Applying HRSTEM imaging under conditions their appearance, Burgers vector or connection to the of Z contrast the chemical width of the interface was channel dislocation network. After selecting a charac- measured to be < 1 nm. Taking into account geometri- teristic dislocation and applying the FIB lamella lift out cal broadening due to atomic scale roughness the actu- technique cross section HRSTEM can be used to reveal al width of the interface is expected to be even smaller. the dislocation core structure and unravel the role the dislocation plays in the creep process. In the present Acknowledgement work the core structures of two characteristic <100> The authors gratefully acknowledge financial support superdislocations which do not experience any glide or by the German Research Foundation (DFG) through climb force from the external load are studied. Interest- the SFB Transregio 103 and the GRK 1229. New Experimental Results on Atomistic and Microstructural Aspects of Creep of Ni-Base Single Crystal Superalloys (SXs) H. Buck, A. Kostka, P. Nörtershäuser, A.B. Parsa, P. Wollgramm, G. Eggeler Institut für Werkstoffe, Ruhr-Universität Bochum, Germany Single crystal Ni-base superalloys (SXs) are directional- positions with respect to the availability of strategic ly solidified cast materials which are used to fabricate alloy elements which become scarce. This holds for ex- blades for gas turbines [1]. Despite numerous ongoing ample for Re. Before such elements can be replaced, efforts, there are presently no alternative high tem- however, their role during soldification, post cast heat perature materials in sight which can replace SXs. SXs treatments and high temperature exposure must be combine good creep strength with reasonable ductility. fully understood. This is one of the research objectives In SX technology, there is a need to adjust alloy com- of the collaborative research center SFB/TR 103 which 311 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 is funded by the German Research Association (DFG). of 140 x 100 x 20 mm3. In a collaborative project where Microstructural heterogeneity on two length scales is several projects work on different aspects of a material a salient feature of SXs. There are dendritic and inter- from one batch, it is important to know which scatter dendritic regions which reflect the cast microstructure one has to expect [2]. Then we show how dislocation of the directionally solidified materials. A typical den- plasticity and rafting affect high temperature and low drite spacing is 500 µm. And the typical length scale stress creep anisotropy [3,4,5]. And finally, an attempt of the γ/γ’-microstructure which forms during the is made to study the interaction of γ-channel disloca- post cast heat treatments is thousand times smaller, tions with γ’-particles. The formation of ledges and 0,5 µm. During processing, alloy elements partition on groves is documented. It is proposed that grooves form both length scales [1]. Thus, on the large length scale, because dislocation stress fields affect local chemical Al and Re partition to interdendritic and dendritic re- potentials and drive diffusional fluxes. All results are gions, respectively. In the γ/γ’-microstructure, on the discussed in the light of previous findings which were other hand, there is more Al in the γ’-phase than in published in the literature. Areas in need of further the γ-channels, while the opposite holds for Re. The work are identified. understanding of the role of these large and small scale heterogeneities is another research objective of SFB/ Acknowledgement TR 103. SXs have a microstructure which consists of The authors acknowledge funding through projects A1 γ’-cubes (edge length: 0,5 µm, volume fraction: 80 %, and A2 of the Collaborative Research Project SFB/TR ordered L12 crystal structure) which are separated by 103 funded by the German Research Association (DFG). thin γ-channels (channel width: 100 nm, volume frac- tion: 20 %, fcc). When this microstructure is exposed References to creep conditions in the 1000°C/100 MPa range, mi- [1] R.C.Reed, The Superalloys: Fundamentals and Ap- crostructural changes occur. γ-channels fill with dislo- plications, Cambridge University Press, Cambridge, cations, dislocation networks form around γ’-particles, UK, 2006. dislocations cut the γ’ phase and directional coarsening [2] Alireza B. Parsa et al., Advanced Engineering Mate- of the γ’-phase, known as rafting, occurs. The present rials, 2014, DOI: 10.1002/adem.201400136 contribution presents some new experimental results [3] L.Agudo Jácome et al., Acta Mater., 61 (2013) pp. which were obtained in the first funding period of SFB/ 2926-2943 TR 103. First, scale bridging microstructural charac-ter- [4] L.Agudo Jácome et al., Acta Mater., 69 (2014) pp. ization and minitature specimen creep testing was 246-264 used to characterize the homogeneity of a cast blade [5] P.Nörtershäuser et al., Mater. Sci. Eng. A, accepted 312 Talks Topic I 3: High temperature materials Talks Topic I 3: High temperature materials 313 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Mechanical properties and microstructures of new polycrys- talline γ/γ’ Co-base superalloys Steffen Neumeier, Lisa Freund1, Mathias Göken Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Materials Science & Engineering, Institute I, Erlangen, Germany Polycrystalline g’ precipitation hardened Ni-base super- by transmission and scanning electron microscopy. alloys are widely used in aircraft gas turbines for rotat- The alloy with higher contents of Ti and Ta possesses ing discs and static components due to their outstand- cubic g’ precipitates while the other alloy shows glob- ing, well-balanced high temperature corrosion resist- ular precipitates. Previous 3D-atom probe tomography ance and strength. However, to improve the turbine investigations could show that Ti and Ta partition pref- operating efficiency, higher inlet gas temperatures and erentially to the g’ phase [3] and thus increase the lat- new materials with enhanced properties are needed. tice parameter of g’. The different precipitate shapes In 2006, Sato et al. [1] discovered a new g’ Co3(Al,W) are, accordingly, a result of the different positive lat- phase with L12 crystal structure in the Co-Al-W system. tice misfit which has been determined by high-energy Hence, new Co-base superalloys with similar micro- synchrotron X-ray diffraction from room temperature structures compared to Ni-base superalloys comprising up to 900°C. Compression tests from RT to 850°C show of coherently embedded g’ precipitates have been de- that a similar yield strength below 800 °C could be veloped [2]. It has been shown, that the yield strength achieved compared to Ni-base superalloys Waspaloy anomaly of Co3(Al,W) is shifted towards higher temper- and Udimet 720Li. At temperatures above 800°C the atures and that high g’ volume fractions at application yield strength is even higher than for the compared temperature can be achieved in Co-base superalloys Ni-alloys. However, the advantage of both g/g’ Co-base although the g’ solvus temperature is lower compared superalloys appears particularly when comparing the to that of Ni-base superalloys. This is benefical because creep properties under compression at 700 °C. The they can be easily forged at high temperatures above investigated Co-base superalloys have a much higher g’ solvus and a high strength can be obtained at ap- creep strength than comparable Ni-base superalloys. plication temperature. Therefore, the g/g’ Co-base su- peralloys have a great potential as a new type of high References temperature wrought alloys. [1] Sato J., Omori T., Oikawa K., Ohnuma I., Kainuma R. In this work, two newly developed polycrystalline g/g’ & Ishida K. – Science 312 (2006) 90 Co-base superalloys with high Chromium content will [2] Bauer A., Neumeier S., Pyczak F. & Göken M. – be presented. After casting and hot-rolling the alloys Scripta Materialia, 63 (2010) 1197 were recrystallised and aged during a three-step heat [3] Povstugar I., Choi P.-P., Neumeier S., Bauer A., Zenk treatment. Both alloys have a fine-grained microstruc- C.H., Göken M. & Raabe D. – Acta Materialia 78 ture with comparably high g’ volume fraction, as shown (2014) 78 Investigation of the quaternary system Co-Al-W-Ta in the range of Co9Al10W2Ta Alexander Epishin1, Thomas Link1, Jan Midtlyng1, Nikolay Petrushin2, Gert Nolze3 1Technical University of Berlin, Germany 2All-Russian Institute of Aviation Materilas, Moscow, Russia 3Federal Institute for Materials Research and Testing, Berlin, Germany Recently a new class of Co-base alloys (Co-Al-W-Ta-X) of Co9Al10W2Ta was selected, because it provides with g/g’-microstructure similar to Ni-base superal- according to [1,3,4] a relatively stable strengthening loys was discovered [1]. Before practical application g’-phase. This composition was systematically varied. however many obstacles have to be overcome, e.g. 2 elements were always kept constant, the other 2 el- low thermal stability of the microstructure (g’-solvus ements varied. Varying the elements Co↔Al, Co↔W, ≤1150°C [2] and precipitation of deteriorating phases), Co↔Ta, Al↔W, Al↔Ta, W↔Ta by ±2 at% gives 12 element partition between g- and g’-phases unfavour- compositions. The as-cast material was investigated by able for solid solution hardening, etc. In order to solve digital scanning calorimetry (DSC), providing the g’-sol- these metallurgical problems, a starting composition vus-, solidus- and liquidus- temperatures. The volume 314 Talks Topic I 3: High temperature materials fraction of the non-equilibrium eutectic was measured Additionally the diffusion mobility of each element of metallographically. Al, W and Ta increase the g’-solvus, the Co-Al-W-Ta system was determined. Here the ho- whereby Ta is 2 times more effective than Al and W. mogenised alloy Co9Al8W2Ta could be used, because However, Ta significantly increases the volume fraction it is single-phase (g) above 1083°C. It was diffusionally of the eutectic, namely up to 30 vol. % at 4 at% Ta. welded with pure cobalt and annealed between 1100 The 12 alloys were grouped in 6 diffusion couples, and 1250°C. From the measured concentration profiles each varying in the same two elements. They were the temperature dependent diffusion mobilities were welded in vacuum at 1050°C/1 h and then annealed calculated. at 1240°C/192 h in order to get broad diffusion zones, then aged for 1000 h/ 900°C to get the equilibrium References microstructure at the temperature of interest. The Sato, J. Omori, T. Oikawa, K. Ohnuma, I. Kainuma, R. specimens were investigated by scanning electron mi- Ishida, K. (2006): Co-base high temperature alloys. - croscopy (SEM), electron probe microanalysis (EPMA) Science, Vol. 312, 90-91. and electron back scatter diffraction (EBSD). The phase Bauer, A. Neumeier, S. Pyczak, F. Singer, R. F. compositions corresponding to different chemical Görken, M. (2012) Creep properties of different compositions were identified. Increase of W and Ta g/g’-strengthened Co-base superalloys, Mater. Sci. above (8W+2Ta) results in precipitation of undesirable Eng., A 550, 333– 341. phases enriched by W/Ta. Pollock, T. M. Dibbern, J. Tsunekante, M. Zhu, J. Su- Identification of small precipitates was performed in zuki, A. (2010) New Co-based high temperature transmission electron microscope (TEM). TEM foils alloys. – JOM, 62, 58-63. were prepared from the samples of the starting alloy Bauer, A. Neumeier, S. Pyczak, F. Görken, M. (2010): and its 12 variations, all homogenised and aged exactly Microstructure and creep strength of different like the diffusion couples. g/g’strengthened superalloy variants. - Scripta Ma- ter., 63, 1197-1200. Influence of rhenium on the local mechanical properties of the γ and γ′ phase in cobalt-base superalloys M. Kolb, C. Zenk, S. Neumeier, M. Göken Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Materials Science & Engineering, Institute, Germany The new class of cobalt-base superalloys with a fcc γ acterize the mechanical properties on the scale of the matrix hardened by coherently embedded Co3(Al,W) γ and γ′ phase. Complementary investigations of the γ/ γ′ precipitates is very interesting for high temperature γ′ partitioning behaviour of all elements by means of applications [1,2]. The melting point of cobalt is about various methods are inevitable to interpret the results 40 °C higher (1495 °C) than the one from nickel which from nanoindentation. It is shown that the addition gives rise to the hope for higher possible service tem- of rhenium influences the partitioning behaviour of peratures and good creep properties [3]. However, in the other alloying elements. This results in a change cobalt-base superalloys the partitioning behaviour of of the measured local mechanical properties of the in- various elements is different to that one in nickel-base dividual phases. Additionally the effect of rhenium in superalloys. The γ matrix in cobalt-base superalloys is cobalt-base superalloys is compared to the effect of not sufficiently hardened since most of the alloying el- rhenium in nickel-base superalloys which has been ad- ements partition preferentially to the γ′ phase. Also the dressed previously [4]. effective solid solution strengthener tungsten mainly partitions to the γ′ phase. As known from nickel-base References superalloys rhenium strongly improves the mechanical [1] J. Sato, T. Omori, K. Oikawa, I. Ohnuma, R. Kainu- properties at high temperatures. This is commonly ex- ma, K. Ishida, Science 312 (2006), 90 plained by the strong partitioning to the γ matrix, the [2] A. Bauer, S. Neumeier, F. Pyczak, R.F. Singer, M. effectiveness as solid solution hardener and its very Göken, MSE A 550 (2012), 333 small diffusion coefficient [4,5]. To further clarify the [3] A. Bauer, S. Neumeier, F. Pyczak, M. Göken, Scripta role of Re it is important to know, if it shows the same Mat. 63 (2010), 1197 effects in cobalt-base superalloys. [4] S. Neumeier, F. Pyczak, M. Göken, Phil. Mag. 91 This work aims to study the local mechanical proper- (2011) 4187 ties of the γ and γ′ phase in a rhenium containing and [5] M.S.A. Karunaratne et al., Proc. 9th Int. Sym. on a rhenium-free cobalt-base superalloy by using nanoin- Superalloys (2000) 263 dentation. This method provides a possibility to char- 315 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Radiation stability of ZrSiN system under the Xe ions irradiation Vladimir Uglov1,2, Vitali Shymanski1, Gregory Abadias3, Gennagy Remnev2, Andrey Suvalov1 1Belarusian State University, Minsk, Belarus 2Tomsk Polytechnic Universuty, Russia 3Institut P’, Poitiers, France Active research in recent years in the study of the struc- nanocrystalline (10 – 30 nm) particles of zirconium ni- ture and properties of nanocrystalline materials have tride ZrN. shown particular promise of composite coatings on the RBS results allowed to determine the concentration basis of ZrSiN, which is characterized by the thermal profiles of the xenon distributed in the ZrSiN coatings, stability of the structure at temperatures up to 1300 °C according to which the maximum concentration of xe- and high mechanical properties [1]. However, there are non increases from 8 to 17 at. % with the dose increas- no any reliable data on the radiation stability of such ing from 5·1016 to 1017 cm-2 (at T=20 ºC). According to structures, which is particularly relevant for their op- the XRD data the lattice parameter of zirconium nitride eration in conditions of high radiation exposure. These ZrN is equal to 0.4572 nm, which corresponds to the materials can be considered as protective materials in lattice parameter of ZrN in the unirradiated system. reactor system of fission. The aim of the present work The implantation of xenon ions at T=800 ºC results in was to study the radiation stability of the ZrSiN system displacement of the maximum concentration to the implanted with Xe ions. depth of about 200 nm that is accompanied by broad- ZrSiN system was formed as a thin film coating on sili- ening of the concentration profile. The lattice param- con substrate by reactive magnetron sputtering of zir- eter of the zirconium nitride ZrN is not changed after conium and silicon target in Ar+N2 (pN = 8.8 mPa) at- xenon ions implantation that can indicate on the stabil- mosphere at temperature of 650 ºC. The power on the ity of the structure for this type of radiation exposure. Zr and Si cathodes was 300 and 250 W, respectively. In The reason for such behavior can be associated with the formed ZrSiN coating the ions of Xe+2 with ener- nanocrystalline particles of zirconium nitride, which gy of 180 keV and the doses 5·1016 and 1017 cm-2 were promotes the migration of radiation-induced defects implanted. The implantation was carried out at room to the interface [2]. (T=20 ºC) and higher (T=800 ºC) temperatures. Thus, it was shown that the structure of coatings ZrSiN, The elemental composition of the ZrSiN system was formed by reactive magnetron sputtering, character- determined on the basis of Rutherford back-scattering ized by the radiation resistance under the xenon ions (RBS), The phase composition was studied by means of (180 keV) irradiation. X-ray diffraction (XRD). The ZrSiN coatings are characterized by uniform distri- References bution of elements across the thickness (600 nm) coat- 1. Musil J., Daniel R., Zeman P., Takai O., Structure and ing, the concentrations being equal to 34 at. % (Zr), 22 properties of magnetron sputtered Zr-Si-N films at. % (Si) and 44 at. % (N). The phase composition of with a high ≥ 25 at.%) Si content // Thin Solid Films. the coating represents by the cubic zirconium nitride 2005. V.478 P.238 ZrN, the lattice parameter of which equals to 0.4572 2. V.V. Uglov, G.E. Remnev, N.T. Kvasov, I.V. Safronov. nm. Diffraction reflections, indicating the presence of Dynamic processes in metal nanoparticles under phases based on silicon have no been identified, how- irradiation. Journal of surface investigation. X-ray, ever, the relation of the concentrations N/Si, being ap- synchrotron and neutron techniques. – 2014. – Vol. proximately equal to 2, allows to suppose [1] an amor- 8, № 4. – P. 703-707. phous matrix of Si3N4 formation with included therein 316 Talks Topic I 3: High temperature materials Effect of casting defects on high cycle fatigue behavior of nickel-based superalloy MAR-M 247 Miroslav Šmíd1, Stanislava Fintová1, Ludvík Kunz1, Pavel Hutař2, Karel Hrbáček3 1Institute of Physics of Materials, AS CR, Brno, Czech Republic 2CEITEC IPM, Institute of Physics of Materials, Brno, Czech Republic 3PBS Velká Bíteš, a. s., Velká Bíteš, Czech Republic High-cycle fatigue tests were performed on the cast cycled at 800 and 900 °C and reasonable agreement polycrystalline superalloy MAR-M 247. The alloy un- for temperature of 650 °C. Fatigue lives were in good derwent hot isostatic pressing treatment and heat corellation with estimated defect sizes from metallo- treatment in order to minimize inherited porosity and graphical analysis. The results obtained from the frac- improve mechanical properties. Fatigue life of the alloy tographical analysis and the metallographic analysis of was determined at temperatures of 650, 800 and 900 °C defect size distribution proved that fatigue behavior of under conditions of constant stress amplitude and fully the MAR-M 247 alloy at 650 °C is not determined just reversed loading regime. After fatigue tests the speci- by defects but also by different damage mechanisms mens were subjected to fractographical analysis with than at temperatures of 800 °C and 900 °C. Crystalo- the aim to localize fatigue crack initiation sites and to graphically dependent crack propagation at 650 °C determine main damage mechanisms. Shrinkage pores smoothly transformed into non-crystalografic trans- or their clusters were found to be typical sites of the granular crack propagation with typical fatigue fracture fatigue crack initiation. Subsequently, metallographic surface features at 900 °C. samples prepared from specimen gauge length were thoroughtly analysed by optical microscope. The analy- Acknowledgement sis of defect size distribution by extreme value statistics This research was supported by Technology Agency of was employed in order to estimate maximum area of a the Czech Republic by project no. TA04011525. Re- defect likely to occur on the area of gauge length cross search team was also supported by CEITEC – Central Eu- section. Estimated defect sizes were matched with ropean Institute of Technology with research infrastruc- obtained fatigue life-times and also with real fatigue ture supported by the project CZ.1.05/1.1.00/02.0068 crack initiation sites observed on the fracture surfac- financed from European Regional Development Fund. es. The results showed good agreement for specimens Finite Element Simulation of the creep behavior of direction- ally solidified NiAl-9Mo Jürgen Albiez1, Ioannis Sprenger2 , Martin Heilmaier2, Thomas Böhlke1 1Institute of Engineering Mechanics, Karlsruhe Institute of Technology (KIT), Germany 2Institute for Applied Materials, Karlsruhe Institute of Technology (KIT), Germany For high temperature structural applications, the rate of the directional solidified NiAl-9Mo can be more B2-ordered intermetallic phase NiAl has promising than five orders of magnitude lower compared to the material properties, such as high oxidation resistance, intermetallic NiAl (Dudová 2011, Haenschke 2010, Hu high melting temperature, high thermal conductivity 2013, Seemüller 2013). It has been shown that these and relatively low density (Johnson 1995). However, as-grown molybdenum-rich fibers are dislocation free the use of NiAl for structural applications suffers from and plastic flow begins, when the fibers’ stress ap- its low creep resistance and its weak room tempera- proaches the theoretical strength (Bei 2007, Bei 2008). ture fracture toughness (Noebe 1993). To improve After start of yielding, the flow stress reduces due to these two material properties at the same time, direc- strain softening of the fibers (Bei 2008). An additional tional solidification of eutectic alloys leads to a forma- advantage of using the directional solidification of eu- tion of stoichiometric NiAl and a reinforcing phase of a tectic alloys is that the phases are thermodynamically refractory metal e.g. Cr, Mo, W, Re (Johnson 1995). A stable even up to the melting point (Johnson 1995). directional solidified NiAl-9Mo (at. %) eutectic consists To be able to predict the directional solidified Ni- of well-aligned single-crystal molybdenum-rich fibers Al-9Mo material behavior under several conditions, embedded in a Ni-50Al matrix. The steady-state creep material models describing each phase are necessary. 317 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Our single crystal plasticity model for large deforma- and the NiAl-(Cr,Mo) eutectic systems – Intermetal- tion is based on a phenomenological approach with a lics 3: 99-113. state variable describing the accumulated slip of the Noebe, R. D. (1993): Physical and mechanical proper- glide systems. We use an overstress type power law ties of the B2 compound NiAl – International Mate- flow rule to model the slip in each slip system and to rials Reviews 38(4): 193-232. consider the elastic range of the fibers. The two phases Dudová, M. (2011): Creep in directionally solidified are modeled by an elasto-viscoplastic approach with NiAl-Mo eutectics – Scripta Materialia 65: 699-702. a voce-softening behavior for the fibers and a perfect Haenschke, T. (2010): Synthesis and characterization plasticity behavior for the matrix. The voce-softening of lamellar and fibre-reinforced NiAl-Mo and NiAl-Cr behavior is motivated by the observation of the strain – Journal of Physics: Conference Series 240. softening of the fibers (Bei 2008). Hu, L. (2013): Tensile creep of directionally solidified A creep curve simulation of a NiAl-9Mo representative NiAl-9Mo in situ composites – Acta Materialia 61: volume element with periodic boundary conditions is 7155-7165. compared to experimental results. The simulation re- Seemüller, C. (2013): Influence of fiber alignment on sults show that the molybdenum-rich fibers carry the creep in directionally solidified NiAl-10Mo in-situ load and reduce the stress in the NiAl matrix. This load composites – Intermetallics 35: 110-115. partitioning leads to a reduction of the steady-state Bei, H. (2007): Compressive strengths of molybdenum creep rate compared to the NiAl intermetallic phase. alloy micro-pillars prepared using a new technique – Scripta Materialia 57: 397-400. References Bei, H. (2008): Effects of pre-strain on the compressive Johnson, D. R. (1995): Processing and mechanical stress-strain response of Mo-alloy single-crystal properties of in-situ composites from the NiAl-Cr micropillars – Acta Materialia 56: 4762-4770. 318 Talks Topic I 4: High temperature materials Talks Topic I 4: High temperature materials 319 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 On the nucleation of Mo-rich Laves phase particles in 12% Cr tempered martensite ferritic steels Aleksander Kostka1, Mehmet Ikbal Isik2, Gunther Eggeler1 1Institute for Materials, Ruhr-University Bochum, Germany 2Max-Planck Institute for Iron Research, Düsseldorf, Germany 12% Cr tempered martensite ferritic steels (TMFSs) Laves phase particles were not detected in the initial are used for critical components in fossil-fired power state. Nucleation begins at micrograin boundaries in plants where they have to withstand mechanical loads the immediate vicinity of micrograin boundary car- at temperatures up to 650°C. The creep strength of bides where Si and Mo segregate from the matrix [3]. these materials strongly relies on M23C6 carbides which That segregation is additionally enhanced by the fact, stabilize the subrgain structure [1]. However, during that growing M23C6 carbides do not dissolve Si and P high temperature exposure Laves phase particles form. and thus pushes these elements towards a micrograin Their compositions are close to (Fe, Cr)2 Mo, and Si boundary [4]. Creep stress and strain have no signifi- plays a key role in their nucleation and growth [2]. cant effect on the early stages of Laves phase forma- The present work focuses on 12 wt.% Cr tempered tion. martensite ferritic steel with 1 wt.% Mo and 0.2 wt.% C (German grade X20CrMoV12-1). High-resolution References characterization techniques, such as analytical trans- [1] Kostka, A., Tak, K.G., Hellmig, R.J., Estrin, Y., Eggeler mission electron microscopy (TEM) and atom probe G. (2007): ,Acta Mater., 55: 539-550. tomography (APT), are used to study the combination [2] Aghajani, A., Somsen C., Eggeler G. (2009): Acta of elementary processes that lead to the formation of Mater., 57: 5093–5106. Laves phase particles. [3] Isik, M.I., Kostka, A., Eggeler, G. (2014): Acta Ma- The material was exposed to 550 °C for time intervals ter., 81: 230-240. between 864 and 81,984 h. For comparison, a few [4] Isik, M.I., Kostka, A., Yardley, V.A., Pradeep, K.G., creep tests were carried out at 550 °C and 120 MPa Duarte, M.J., Choi, P.P., Raabe, D., Eggeler, G. (2015): (duration between 864 and 12,456 h). All tests were Acta Mater., submitted. interrupted after specific time periods and microstruc- tures were investigated. Temperature dependent solid solution strengthening of Nickel by transition metal solutes Hamad ur Rehman1, Karsten Durst2, Steffen Neumeier1, Roger Reed3, Mathias Göken1 1Friedrich-Alexander-Universität Erlangen-Nürnberg, Materials Science and Engineering, Institute-I, Germany 2Institute of Physical Metallurgy, TU Darmstadt, Germany 3Department of Engineering science , University of Oxford, UK Rhenium (Re) is an important g-matrix strengthening ute followed by W and Re, irrespective of the applied solute for improving the creep properties of single strain rate. At T ≥ 1000°C, Re becomes a better solid crystalline nickel based superalloys. It improves the solution strengthener than Ta at a slower strain rate creep life of these alloys due to its slow diffusion co- (10-5). This effect is further amplified at 1200°C, where efficient1, as the diffusion controlled climb of disloca- Re is a better solute at all the strain rates. This effect tions at the g-g, interfaces is the rate controlling step is caused by temperature and strain rate dependent during creep at high temperature and low stress2. In strengthening mechanisms. At RT, solutes exert pin- the present work, temperature dependent solid solu- ning forces on moving dislocations and the strengthen- tion strengthening of Nickel was studied using strain ing effects could be explained using Labusch theory3. rate jump tests on (100) oriented single crystalline Ni At high temperatures (T>0.5Tm) solute atoms create a and binary Ni-2 at. % X (X=Ta,W,Re) alloys at RT and be- Cottrell atmosphere4 by accumulating on moving dis- tween 800-1200°C. The applied strain rate is varied in locations that exert a drag force on the dislocations. the range 10-3-10-5. The results show that at tempera- Mathematical modeling was used to calculate this sol- tures up to 800°C, Ta is the strongest strengthening sol- ute drag. It was shown that Re atoms exert a higher 320 Talks Topic I 4: High temperature materials drag force on the moving dislocations in contrast to W Ni–Ta and Ni–W systems between 900 and 1300°C. and Ta. Furthermore, Re atoms reduce the diffusion Mater. Sci. Eng. A 281, 229–233 (2000). controlled climb of dislocations. This combined effect 2. Reed, R. C. The superalloys fundamentals and appli- of reduced diffusion controlled climb and higher solute cations. (Cambridge University Press, 2006). drag is responsible for Re being a better solute for Nick- 3. Labusch, R. Statistische theorien der mischkristall- el at higher temperatures and slow strain rates. härtung. Acta Metall. 20, 917–927 (1972). 4. Cottrell, A. H. & Jaswon, M. A. Distribution of Solute References Atoms Round a Slow Dislocation. Proc. R. Soc. A 1. Karunaratne, M. S. ., Carter, P. & Reed, R. . Interdif- Math. Phys. Eng. Sci. 199, 104–114 (1949). fusion in the face-centred cubic phase of the Ni–Re, Effect of the Stress Multi-Axiality on the Creep Damage in Fine Grained HAZ of Mod. 9Cr-1Mo Steels Kimiaki Yoshida1, Masataka Yatomi2, Masaaki Tabuchi3, Ken-ichi Kobayashi4 1IHI Corporation, Yokohama, Japan 2IHI Asia Pacific, Singapore 3National Institute for Materials Science, Tsukuba, Japan 4Chiba University, Chiba, Japan High-chromium ferritic heat resisting steels have been In this study, circumferentially notched bar creep rup- used for structural components at elevated tempera- ture and interrupted tests have been conducted on ture, because of their excellent creep properties. How- simulated HAZ specimens of mod. 9Cr-1Mo Steels. Me- ever it is well known that creep strength of the welded tallographic examination has been carried out to quan- joints of these steels is decreased during long-term use tify creep damage accumulation in the specimens. at higher temperatures due to Type-IV creep damages From the experimental results, it has been founded formed in the fine grained heat affected zone (HAZ). that stress multi-axiality has a significant effect on Fine grained HAZ are subjected to complex multi-axial the creep damage and rupture time of the notched stress conditions due to constraint effect on the de- bar specimens. Finite element predictions based on formation from the base and weld metals. It has been a continuum damage mechanics model with ductility pointed out that the stress multiaxiality has an influ- exhaustion approach have been proposed to predict ence on creep damage evolution. It is, therefore, need- the creep damage and rupture time under multi-axial ed to identify the effect of multi-axial stress condition stress conditions and applied to the notched bar spec- on creep damage in fine grained HAZ and to predict the imens. Compared with the experimental results, it has creep rupture and the creep damage under multi-axi- been concluded that the ductility exhaustion approach al stress conditions for preventing the type IV fracture provides reasonable life predictability almost in a scat- precisely. ter band of a factor of 2. Thermal stability of ferritic and austenitic nanocluster con- taining ODS steels Sascha Seils1, Daniel Schliephake1, Daniel Janda1, Alexander Kauffmann1, Julia N. Wagner1,2, Martin Heilmaier1 1Karlsruhe Institute of Technology (KIT), Institute for Applied Materials, Germany 2Karlruhe Nano Micro Facility, Germany Oxide dispersion strengthened (ODS) steels became g. advanced steam turbines or solar technology. These a promising materials class for applications in future superior material properties result most likely from the fusion and fission power plants due to their excellent formation of very fine distributed, nanoscaled (< 4 nm) resistance against swelling under radiation. Addition- and thermodynamically stable Y-Ti-O clusters. ally they show high temperature stability and excellent Although it was shown that the addition of micro al- creep behavior, which opens a field of application to e. loying elements like titanium can significantly decrease 321 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 the size of these clusters in ferritic ODS steels [2], the does not result in a significant Ostwald ripening, which mechanisms of their formation is not completely un- might be hindered effectively by nanoclusters pinning derstood, yet. As well, detailed knowledge about the the grain boundaries. The grain size was determined development of these clusters at high temperatures is to be about 300 nm after consolidation and heat treat- crucial to further improve the microstructural stabili- ment, respectively. Atom probe tomography (APT) ty during annealing and the creep resistance. While technique enables the visualization of Ti-Y-O-rich clus- the processing of ferritic ODS steels was established ters which have a size of 3 to 4 nm, only. Slightly larg- for years, the synthesis of the austenitic counterpart er clusters could also be found in austenitic samples, revealed several challenges in the past. However, due resulting in a comparable thermal stability of the mi- to their crystal structure austenitic ODS steels are sup- crostructure. Furthermore, the influence of cluster size posed to have even better high temperature properties and distribution on the outstanding creep properties regarding creep behavior. will be presented. In this contribution, we show results on the thermal stability of two ferritic ODS steels, differing in contents References of yttria and titanium in comparison to an austenitic [1] Schneibel, J.H. et al., (2009): Ultrafine-grained na- ODS steel with similar composition. The samples were nocluster-strengthened alloys with unusually high mechanically alloyed by high energy ball milling of ele- creep strength – In: Scripta Mater. 61; 793-796. mental or pre-alloyed powders and compacted by field [2] Ukai, S. & Fujiwara, M. (2002): Perspective of ODS assisted sintering technique (FAST). Electron backs- alloys application in nuclear environments – In: J. cattering diffraction (EBSD) results on the ferritic ODS Nucl. Mater. 307-311; 749-757. steels show, that even annealing at 1000 °C for 1000 h Microstructure and micromechanics of directionally solidi- fied eutectic alloys Amritesh Kumar, Ruth Schwaiger, Oliver Kraft Institute for Applied Materials (IAM-WBM), Karlsruhe Institute of Technology (KIT), Germany The ever increasing demand to improve the efficiency rectional solidification at three different solidification of high temperature structural applications such as gas speeds (20 mm/h, 50 mm/h and 80 mm/h respectively) turbine engines, requires development of materials where NiAl forms the matrix and Cr forms continuous with better properties such as lower density, higher fibers with fiber diameter ranging from about 800 nm operating temperature, and higher fracture toughness. for 20 mm/h samples to about 250 nm for 80 mm/h Nickel aluminides has gained a lot of attention as a can- samples. didate for next generation high temperature structural We have employed different micromechanical tech- material, owing to their superior properties such as, niques to characterize the material at different length high melting point, good oxidation resistance, and low scales including nanoindentation, in-situ tensile test density. While low ductility and fracture toughness at of the fibers and micro-pillar compression tests, and room temperature and insufficient high temperature first results will be presented in this paper. Hardness strength have been identified as major drawbacks of and modulus of the overall alloy obtained by nanoin- nickel aluminides, alloying with refractory metals has dentation appears to be independent of the solidifica- shown to improve their properties. Producing these tion speeds. The modulus values correspond well with alloys by directional solidification results in a highly those reported in literature. Micro-pillars containing aligned microstructure with the refractory metals to single Cr fibers surrounded by the matrix were fab- form continuous fibers or laminates. This microstruc- ricated using Focused Ion Beam milling for compres- ture enhances creep properties, fracture toughness sion testing to evaluate the strength of the composite and microstructural stability. The diameter of the fib- on small scale. The strength of micro-pillars shows a ers and the spacing between the fibers depend on the weak dependence on the fiber diameter with smaller speed of directional solidification. Thus, it is important diameter pillars showing higher strength. Micro-pillar to investigate the mechanical behavior of these mate- compression tests also suggest that the interface be- rials at varying length scales in order to understand in tween fiber and matrix is rather strong as no delamina- detail relationships between microstructure, process- tion or fracture at the interface was observed in any of ing parameters and alloying additions on the macro- the tests. Currently, micro-pillar testing of the individ- scopic properties of the material. The starting material ual phases is being carried out in order to investigate for this study is NiAl-Cr eutectic alloy, prepared by di- the role of the interface for the deformation behavior. 322 Talks Topic I 4: High temperature materials Moreover, Cr fibers were isolated from the matrix by formation preceded the fracture. These investigations chemical etching and in-situ SEM tensile tests of these demonstrate that the individual phases of the direc- isolated fibers were carried out. It was observed that tionally solidified alloy are intrinsically not brittle and, the single-crystalline fibers deformed to plastic strains thus, it is conceivable that the highly ordered alloys can of several percent and that for most fibers tested neck reach reasonable toughness at large scale. 323 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic I 5: High temperature materials 324 Talks Topic I 5: High temperature materials Tungsten (W) laminate pipes made of ultrafine-grained (UFG) W foil Jens Reiser, Simon Bonk, Jan Hoffmann, Michael Rieth1 Karlsruhe Institute of Technology, Institute for Applied Materials, Germany Tungsten (W) is the metal with the highest melting starting point of the synthesis of a W foil laminate, a point of all metals (3422°C) and would therefore be an multi-layer material. Through the synthesis of a tung- excellent fit for structural high temperature applica- sten laminate, the properties of the foil can be trans- tions. One disadvantage that impedes the use of tung- ferred to the bulk and by rolling up and joining tung- sten for structural parts is its low room temperature sten laminate pipes can be produced [Reiser, 2014]. (RT) fracture toughness, KIC, and its high brittle-to-duc- The technical maturity of these W laminate pipes has tile transition temperature (BDTT). However the situ- been approved by high heat flux tests performed at the ation appears different for tungsten in the shape of a Plataforma Solar de Almería, Spain, as well as at the highly cold rolled ultrafine-grained (UFG) foil. Max Planck Institute of Plasma Physics, Garching, Ger- Tungsten foil in the as-rolled (and stress relieved) con- many [Reiser, 2014]. dition has exceptional mechanical properties in terms Within this presentation we give an overview of W of ductility [Wei, 2008], toughness [Pippan, 2011], laminate material in general and of W laminate pipes in and brittle-to-ductile transition (BDT) [Németh, 2015]. particular. This includes aspects like (i) the mechanisms Wei and Kecskes [Wei, 2008] evaluated the tensile of the exceptional mechanical properties of UFG W foil, behaviour of commercially pure W as a function of (ii) the temperature stability of the mechanical proper- low-temperature rolling. They observed that rolling ties of the UFG W foil, (iii) the joining techniques used below the nominal recrystallization temperature of to produce W laminate plates, as well as the evolution 1523 K (1250°C) concomitantly enhances the strength of their interfaces during ageing, (iv) the change of the and ductility of W. Furthermore Pippan [Pippan, 2011] Charpy impact properties of W laminates during ageing assessed the fracture toughness of pure W foil with a and (v) the production of a 1000 mm long W laminate thickness of 160 µm in the as-rolled condition. He de- pipes and their possible application for innovative high termined a RT fracture toughness, K , of 70 MPa(m)1/2IQ temperature energy conversion systems. in L-T direction and of 55 MPa(m)1/2 in T-L direction. Finally Németh et al. [Németh, 2015] evaluated the References nature of the BDT of annealed coarse-grained and Wei Q, Kecskes LJ. Mat Sci Eng A-Struct 2008;491:62. as-received ultrafine-grained (UFG) tungsten foil. For Pippan R, presented at W conference, organized by the UFG tungsten foil he determined a BDTT of about Odette GR, UCLA, Santa Barbara, USA, February 77 K arguing that the BDT in UFG tungsten is controlled 2011. by the glide of edge dislocations. These exceptional Németh AAN, Reiser J, Armstrong DEJ, Rieth M. Int J mechanical properties might be attributed both to the Refract Met H 2015;50:9. positive response of tungsten to cold rolling and the Reiser J, Rieth M, Möslang A, et al. Tungsten (W) lam- ultrafine-grained microstructure of the tungsten foil. inate pipes for innovative high temperature energy Our approache to make W ductile makes use of the ex- conversion systems, Adv Eng Mater, DOI: 10.1002/ ceptional properties of UFG W foils. These foils are the adem.201400204 (article in press). Internal Friction and Shear Modulus Temperature Depend- ence of 9%Cr Ferritic Steel P92 in 25 ÷750°C Temperature Range Elguja Kutelia1 , George Darsavelidze 1, Tengiz Kukava 1, Temur Dzigrashvili1, Ia Kurashvili1, Francisco J. Perez Trujillo 2 1 Georgian Technical University, Tbilisi, Georgia 2 Universidad Complutense de Madrid, Spain The creep rate in practical steels, especially in ferritic ute atoms rather than vacancies. Chromium is an ex- 9%Cr steels (P92), is controlled by the diffusion of sol- ceptional solute because the size difference of Cr ver- 325 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 sus α-Fe is very small. Consequently, its diffusion plays 770°C/60min. Additional heat treatment after the first an important role in the formation of precipitates in measurement was conducted directly in the relaxom- the steel matrix at early stages as well as in the final eter via annealing at 950°C/20min, after which Q-1(t) formation of stable phases during a long-term ther- and ƒ2(t) were measured repeatedly. Two maxima of mo-mechanical impact. It is also important that the internal friction were revealed at temperatures 570°C above steel contains many minor alloying elements, and 650°C, accompanied by shear modulus defects. In and therefore, actual estimation of the diffusion pa- the temperature range 300-750°C reduction of shear rameters and mechanical properties at service tem- modulus occur with different rates, depending on pre- peratures is not easy in heat-resistant steels. Devel- vious heat treatment of the sample. The first maximum opment of methods of substructural strengthening of is determined to be of relaxation nature, and is char- alloys requires a deep insight of the processes of for- acterized by the activation energy of ~52000 cal/mol mation and stabilization of substructure. The latter ne- and the relaxation time constant equal to 10-14sec. cessitates use of structure-sensitive methods, among According to its activation features, the maximum at which the method of internal friction is most efficient. 570°C may be attributed to the relaxation rearrange- The temperature dependences of Q-1(t) and ƒ2(t) were ment of couples of chromium atoms during diffusion measured in the relaxometer with the reverse tor- in α-phase through a Zenner mechanism of relaxation sion pendulum at frequencies ~1Hz and amplitudes in the bcc substitution alloys. The temperature of the of deformation 10-5÷10-3 in the temperature range second maximum does not depend on the oscillation 25 ÷750°C, with the rate of heating/cooling 2°C/min. frequency. Its shape, intensity and temperature con- For the first measurement the samples were cut and siderably changes in accordance to cooling/heating machined to a size (1x1x50)mm3 out of bulk coupons, rate, amplitude of deformation and annealing time at previously normalized at 1060°C/20min + tempered at temperatures lower than α-γ transformation point. Bayesian approach to determine optimum inspection inter- vals for struc tural components of high temperature materi- als subjected to creep Kyoko Nakamura, Yuji Nakasone Tokyo University of Science, Japan Besides state-of-the-arts materials, the develop ment tures (Prager 2000). Since pred icted residual creep life of advanced maintenance technology is a vital issue for varies (Nonaka 1997, Nakasone 2015), it is assumed extending the life of energy conserv a tion facilities. Con- that creep strain to monitor at an arbitrary time is a dition-based mainten ance (CBM) is one of the promis- random variable having the mean obtained by the ing technologies for improving the depend ability, i.e., Monkman-Grant relation and a variance which re- the reliability plus availabi lity of the facilities. Effective mains constant with time. monitori ng technologies includ ing maintenance strate- The fracture probability Pf of a high temperature struc- gies provide the key to success in CBM. tural component is formulated based on the Bayes’ Kitagawa et al. considered an effect of inspections for theorem. The optimum inspection intervals for the cracks of pressure vessels and have proposed a proba- structural component is calculated for different types bilistic strategy for determining optimum inter vals of of in-service-inspection (ISI) models with real main- in-service inspections (Kitagawa 1977). Many of ener- tenance operations taken into consideration; i.e., gy conservation facilities are used at high temperature time-based-model (TBM) in which equal interval for and their lives are greatly influenced by creep damage. ISI is assumed and CBM model in which intervals are For these facilities, CBM may adopt creep strain as the varied with the magnitude of creep strain monitored. target parameter to monitor instead of crack size for “Replace ment” and “repair” models have been also assessing the actual conditions of structural comp o- investi gated. The “replacement” model simulates TBM nents of the facilities. and/or CBM in which a component is found ruptured The present paper proposes a Bayesian approach to and is replaced with a new one having zero creep determine optimum inspection intervals for the struc- strain. The “repair” model simulates TBM in which tural components of high temperature mater ia ls sub- creep strain of a component is reduced to a certain ex- jected to creep. The Monkman-Grant relation or the tent if the creep strain exceeds a given critical value at omega method is adopted to make the residual life a k-th ISI interval where k is a natural number. In the prediction of components in high temperature struc- case of CBM, however, a creep strain of a component 326 Talks Topic I 5: High temperature materials is relaxed just when the creep strain is found to exceed Prager, M. (2000): The omega method – an engi- the critical value. neeri ng approach to life assessment – In: Trans. Variations of the fracture probability of each model of ASME, Journal of pressure vessel technology: with the number of inspections or with time are calcu- 122(3): 273-280. lated and compared by using creep data obtained for Nonaka, I. et al. (1997): Evaluation of Creep Residual modified 9Cr-1Mo steel. Life for Mod. 9Cr-1Mo Steel Based on Omega Meth- od, J. of the Soc. of Mats. Sci., Japan, 45(4): 438-442 References (in Japanese). Kitagawa, H. & Hisada, T. (1977): Reliability Analysis Nakasone, Y. & Suzuki, H. (2015): To be presented at of Structures under Periodic Nonde struc tive Inspec- Materials and Mechanics Conf., Japan Society of tion. – In: Proc. of 3rd Int. Conf. on Pressure Vessel Mechanical Engineers: Kanagawa, Japan. Tech., 1: 475-480; Tokyo, Japan. Microstuctural study on the intermetallic compound NiAl-Cr Antje Krueger, Michael Klimenkov, Anton Moeslang KIT, Institute for Applied Materials, Eggenstein-Leopoldshafen, Germany Structural materials for energy efficient applications <100> direction parallel to the growth direction. At the are developed emphaticly over the past decades. interface of the NiAl and the Cr pahse periodic inter- Therefor the intermetallic NiAl seems to be a good face dislocation networks exist with an average dislo- candidate. It has a low density and good corrosion as cation spacing of around 96 nm. Cline et al. found 70 well as oxidation resistance, but at temperatures high- nm (Cline et al., 1971). These dislocation networks can er than 600 °C the creep resistance gets weak. Refrac- hinder the motion of dislocations when applying a cer- tory elements, e.g. Chromium, Molybdenum and Rhe- tain stress. This is also observed by Chen et al. (Chen et nium, can strengthen the NiAl alloy by forming fibers / al., 1995). If the stress is high enough dislocations will lamellae. During the directional solidification the fibers be able to bridge, cut or surround the fibers. / lamellae are well aligned in the NiAl matrix and can These results give information about the creep mech- be used for turbine blades, e.g. in gas turbines engines. anisms responsible for deformation at high tempera- In our investigation we analyze the creep behavior and tures. microstructure of the intermetallic compound NiAl-Cr. Therefore compressive creep measurements are per- References formed under constant conditions (temperature > 900 Chen X.F. et al. (1995): Deformation and fracture of a °C and applied stress range 100 - 300 MPa). Then the directionally solidified NiAl-28Cr-6Mo eutectic alloy microstructure of the crept specimen is analyzed by – In: J. Mater. Res., 10: 1159-1170. means of transmission electron microscopy. We found Cline et al. (1971): The variation of interface dislo- from selected area diffraction pattern that both phas- cation networks with lattice mismatch in eutectic es, the NiAl matrix and the Cr-fibers are oriented in alloys – In: Acta Metallurgica, 19: 405 – 414. The crystallographic template effect preceding the formation of stable α-Al2O3 during low temperature oxidation of Fe-Al alloys Pedro Brito1, Haroldo Pinto2, Anke Kaysser-Pyzalla3 1Pontifical Catholic University, Mechanical Engineering, Belo Horizonte, Brazil 2University of São Paulo, Materials Engineering, São Carlos, Brazil 3Helmholtz Zentrum Berlin for Materials and Energy, Germany Many materials designed for high temperature appli- oxide film is generally understood as being preceded cations, such as Fe-Al or Ni-Al alloys, rely upon a sta- by the appearance of less protective metastable Al2O3 ble corundum structured α-Al2O3 scale for corrosion polymorphs which usually develop at temperatures and oxidation resistance. The formation of this passive below 1000ºC in the initial stages of oxidation and only 327 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 later transform into the stable α-Al2O3 modification. Hence, the presence of a template oxide may have a The formation of these transient Al2O3 polymorphs has significant impact on the oxidation resistance of Fe-Al a negative impact on the oxidation resistance of the al- alloys, since it reduces the possibility of metastable loys due to their rapid growth rate and also because Al2O3 development in the oxide scale. With the objec- their subsequent transformation to α-Al2O3 induces tive of further investigating the template effect on the large tensile stresses in the oxide scale, which may lead nucleation of stable α-Al2O3 in thermally grown oxide to its failure, exposure of the substrate and increase of layers, in the present work the oxidation of binary Fe- degradation rates (Grabke, 1999). Al alloys was analysed in-situ by applying synchrotron While the formation mechanism of stable α-Al2O3 films X-ray Diffraction (XRD) and also ex-situ by Raman Spec- has been well established for Ni-Al alloys, less is known troscopy at different oxidation times. Raman Spectros- regarding the phase formation during oxidation of Fe- copy is interesting in the present case because it allows Al. Oxidation of Fe based aluminides is significantly for estimating the amount of Al+3 present in the α-Fe2O3 different from Ni-Al alloys because at low and interme- structure in substitution of Fe+3 ions (Zoppi et al, 2007). diate temperatures, Fe (or Cr, which is also commonly The experiments were complemented by texture anal- present) reacts with O before Al to form a precursor ysis using synchrotron XRD and by examining the oxi- oxide (α-Fe2O3 or α-Cr2O3) with the same crystal struc- dized surfaces via Scanning Electron Microscopy. ture of α-Al2O3. The isostructural oxide, which may also be an Al-containing solid solution, acts as a template References for the nucleation of stable α-Al2O3, accelerating the Grabke, H. J. (1999): Oxidation of NiAl and FeAl. – In- formation of the protective layer. In recent investiga- termetallics, 7: 1153-115. tions, this template effect was shown to be active in Kitajima, Y., Hayashi, S., Nishimoto, T., Narita, T. & thin Fe layers deposited on Fe-Al substrates which Ukai, S. (2011): Acceleration of Metastable to Al- were then submitted to isothermal oxidation (Kitaji- pha Transformation of Al2O3 Scale on Fe–Al Alloy by ma et al, 2011). Upon oxidation of the coated mate- Pure-Metal Coatings at 900 °C. – Oxid. Met. 75: 41-56. rials, the deposited Fe was oxidized to form α-Fe2O3, Brito, P., Pinto, H., Genzel, Ch., Klaus, M. & Kayss- which served as a site for heterogeneous nucleation of er-Pyzalla, A. (2012): Epitaxial stress and texture in α-Al2O3 causing either the suppression of metastable thin oxide layers grown on Fe-Al alloys. – Acta Mat. Al2O3 formation or the acceleration of the metastable 60: 1230-1237. to α-Al2O3 transformation. Another aspect that follows Zoppi, A., Lofrumento, C., Castellucci, E. M. & Sciau, this template mechanism is that the thermally grown Ph. (2007): Al-for-Fe substitution in hematite: the α-Al2O3 inherits the crystallographic orientation of the effect of low Al concentrations in the Raman spec- precursor oxide (Brito et al, 2012). trum of Fe2O3. – J. Raman Spec. 39: 40-46.. 328 Talks Topic K 1: Polymer based composites Talks Topic K 1: Polymer based composites 329 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Integrative simulation of short glass fibers reinforced poly- amides: methodology followed to identify polymer matrix constitutive models on a wide range of solicitations, temper- ature, moisture and strain rate Gilles Robert, Olivier Moulinjeune Solvay Engineering Plastics, Technyl Innovation Center, Saint Fons, France Integrative simulation has raised a growing interest volume strain of specimens. Solicitations applied have recently among glass fibers reinforced users. A num- been static tensile, compressive and shear. Static tests ber of industrial solutions has appeared recently to have been completed with dynamic tensile testing. perform such simulations, the more widespread being Many developments have been made on matrix consti- Digimat, edited by e-Xstream. tutive models identification by reverse engineering. It Integrative simulation allows taking into account injec- has been proved that measured orientation data were tion molding process, which generates glass fiber ori- key to obtain accurate results. The number of tensile entation in Finite Elements Analysis (FEA). Given mate- curves necessary to achieve reliable results has also rial anisotropy, this can lead to a spectacular increase been tested. in FEA accuracy. However, to take advantage of this Modeling strategy of the different parameters of ma- technology: (i) glass fiber orientation computed must trix constitutive models is based on time temperature be accurate enough; (ii) the constitutive model of the superposition. A method has been found to integrate matrix must be accurate. strain rate, temperature and moisture concentration in This paper focuses on the methodology followed to a single parameter. Through this approach it becomes identify constitutive models on PA66 matrix optimized very easy to predict matrix behavior in a large domain for integrative simulation and on the modeling strate- of environmental conditions, in tension as well as in gies developed to take into account relevant variables: compression, with some interesting insights about ten- temperature, strain rate, moisture uptake of the ma- sion-compression asymmetry. terial and nature of the solicitation applied (tension, Identifications have proved extremely efficient of spec- compression, and shear). imens, with very small differences between computed Some preliminary points have a strong importance on and measured data. Moreover constitutive models ob- constitutive models accuracy. Specimen must be ma- tained have been widely tested during FEA of complex chined in molded plaques whose geometry is carefully structures, implicit as well as explicit and have proved chosen in order to achieve a good level of microstruc- extremely performing. ture homogeneity. This cannot be achieved with any geometry. A careful choice must be done about plaque References geometry and specimen machining positions. Moreo- Maurel-Pantel A., Baquet E., Bikard J., Billon N. (2011): ver, such choices cannot be considered without a con- Coupled Thermo Mechanical Characterization of trol of glass fiber orientation based on experimental Polymers Based on Inverse Analyses and IR Meas- measurements and not on simulations only. urements - Applied Mechanics and Materials ; A method of glass fiber orientation measurements 70:393-398. through X-ray micro computed tomography has been Kammoun S., Doghri I., Adam L., Robert G., Delan- developed. Orientation tensors were extracted from nay L., (2011): First pseudo-grain failure model for initial volumes images and have allowed an optimal inelastic composites with misaligned short fibers - control of specimen orientation and homogeneity. Composites Part A-applied Science and Manufactur- Measured orientation data has proved much more ac- ing ; 42(12): 1 892-1902. curate than any software simulations to characterize Buffière J.Y. , Maire E. , Adrien J. , Masse J.P. , Boller E. microstructure of reinforced PA66. (2010): In situ experiments with X-ray tomography: Mechanical characterizations of reinforced materials An attractive tool for experimental mechanics - Ex- have been led on a wide set of materials, temperature, perimental Mechanics 50, 289-305. moisture and strain rates, with a videometric control of 330 Talks Topic K 1: Polymer based composites X-ray microtomography and finite element modelling of the failure mechanism in epoxy syntactic foams under compres- sive loads Peifeng Li, Ruoxuan Huang School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore Epoxy syntactic foams containing glass or ceramic mi- cenospheres. The stresses of individual cenospheres croballoons have been increasingly used in transport concentrate in the equator normal to the loading direc- applications due to their high strength-to-weight ratio tion and decrease with the distance from the equator. and excellent energy dissipation capability (Li 2009). Both XMT and FEM revealed that the large cenospheres The bulk mechancial behaviour of syntactic foams is crush first in the foam by the longitudinal splitting frac- instrinsically determined by the properties of various ture along the compression direction. Subsequently, phases in the foam and the unit cell structures such the cenospheres nearly in the transverse (cross-sec- as the geometry and distribution of microballoons. Re- tional) plane progress to crush, leaving the voids in the cent developments in x-ray microtomography (XMT) matrix. Meanwhile, micro-cracks arise in the matrix have allowed 3D characterisation of various micro- where the stresses concentrate and then propagate to structural phases in materials including syntactic foams join the adjacent micro-cracks and voids, thus forming (Awaja 2009, Yu 2012). Finite element modelling (FEM) damage bands (macro-cracks) in the transverse plane. has been the effective tool to analyse the stress field The internal failure mechanism of the syntactic foam and to further characterise the constitutive behaviour can be summarised to be the layered crushing mode. of materials (Li 2015). This work investigated the failure mechanism in syntactic foams especailly in the constit- References uents: the epoxy matrix and cenospheres (ceramic mi- Li, P., Petrinic, N., Siviour, C.R., Froud, R. & Reed, J.M. croballoons) using the combined XMT and FEM meth- (2009): Strain rate dependent compressive proper- od. ties of glass-microballoon epoxy syntactic foams. – In-situ compression experiments in the XMT machine Mater. Sci. Eng. A, 515: 19-25. were conducted on cenosphere epoxy syntactic foams Awaja, F. & Arhatari, B.D. (2009): X-ray Micro Comput- to track the internal microstructural changes at various ed Tomography investigation of accelerated thermal deformation stages. A FE model of the full scale foam degradation of epoxy resin/glass microsphere syn- containing randomly distributed cenospheres were de- tactic foam – Compos. A, 40: 1217-22. veloped to predict the stress and damage evolution of Yu, M., Zhu, P. & Ma, Y. (2012): Experimental study the constituents in the foam. A good agreement was and numerical prediction of tensile strength proper- obtained between the FE predictions and the XMT ob- ties and failure modes of hollow spheres filled syn- servations of the foam under compressive loads. tactic foams – Comput. Mater. Sci., 63: 232-43. It was found that the localised stresses in cenospheres Li, P. (2015): Constitutive and failure behaviour in se- are noticeable higher than those in the matrix, indi- lective laser melted stainless steel for microlattice cating that the main load bearing constituents are the structures – Mater. Sci. Eng. A, 622: 114-20. Mechanical Properties of CFRTP Made from CF/PA Compos- ite Yarn Sutured with PA Fiber Yuji Takubo1, Hiroaki Kimura1 Takashi Matsuoka1, Tomoko Hirayama1, Hiroyuki Fujita2, Yasuji Miyata3, Kunio Fujii4 1 Department of Mechanical Engineering, Doshisha University, Japan 2 Hyogo Prefectural Institute of Technology, Japan 3 Miyata Fabrics Co., Ltd, Japan 4 Toho Textile Co., Ltd, Japan The thermoplastic composite materials is widely used of its high viscosity. In this study, CFRTP was developed from the standpoint of productivity and recycling. with using the composite yarn which sutured rein- However, it is well known to be difficult to impregnate forcement fiber (carbon fiber) and core matrix fibers the thermoplastic resin to reinforcement fiber because (PA6 fiber) by using Mellow Sawing Machine with plat- 331 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 ing fibers (PA6 fiber), and it was confirmed that the im- It was confirmed that the fiber volume content of pregnation state of resin into the carbon fiber bundle CFRTP could control to about 35%-45% by changing the was improved. And also, the composite yarn was made number of core matrix fibers. by suturing two kinds of yarns which the core matrix The impregnation state was investigated from the fibers were oriented parallel to the reinforcement fiber cross-sectional SEM observation. As a result, it was bundles. So, as a characteristic of this composite yarn, confirmed to have a good impregnation state as in- the interfacial adhesion state of the carbon fiber and creasing the core matrix fibers. And the fiber content PA6 resin is expected to improve by the impregnation. rate becomes low in that case. In addition, the composite yarn is possible to control The three-point bending test was performed in ac- the fiber volume content by changing the number of cordance with JIS K7074. As a result, it was clear that core matrix fibers easily. The treatment of composite the bending strength became higher on the low fiber yarn is important to get a good interfacial adhesion content type, because the impregnation of resin into state on the composite material. The machine oil and the carbon fiber bundle was good. contamination adhere to the surface of CF/PA6 com- It was shown that the bending strength of acetone posite yarn through manufacturing process, and they treatment CFRTP have been increasing about 200% in are more likely to produce some voids and the non-im- comparison with that of the non-treatment CFRTP. It pregnation region in the composite materials. There- was confirmed that the acetone treatment was an use- fore, an acetone treatment was performed for the pur- ful method to obtain a good interfacial adhesion. pose of removing them on the composite yarn. In ad- The impact absorption energy was evaluated by the dition, a good impregnation state can be expected by penetration impact testing. As a result, it was shown removing the sizing agent of carbon fiber. The acetone that the impact absorption energy decreased on the treatment can be performed easily under the state of low fiber content type because of the brittle material. the composite fabric, even if the sizing agent of carbon fiber is removed. The following results were obtained from this study; Overall mehanical properties of composites with complex orientationally distributed microstructures Olesya I. Zhupanska, Pavlo Krokhmal Department of Mechanical and Industrial Engineering, University of Iowa, USA This study is concerned with development of bounds to achieve perfect alignment of individual nanotubes, on the elastic properties of fiber reinforced composites and, therefore, nanotubes’ orientational distribution with arbitrary orientational distribution of fibers. The must be taken into account in determination of effec- main motivation comes from study of the effects of the tive properties of buckypaper nanocomposites. orientational distribution of carbon nanotubes (CNTs) In this paper, a generalization of various microme- in buckypapers on the overall elastic properties of CNT chanical approaches (including the Mori-Tanaka model buckypaper polymer matrix composites. (Mori & Tanaka 1973) and Hashin-Schtrikman varia- Buckypapers are thin sheets of porous carbon nano- tional bounds (Hashin & Shtrikman 1963) to the cas- tubes networks that are prepared by a multi-step es of non-aligned composite phases will be examined. process of dispersion and filtration of nanotube sus- Orientation distribution function (ODF) is used to de- pension. Bulk buckypaper polymeric composites are scribe CNT orientation distributions in buckypaper. Giv- obtained by impregnation of nanotube buckypapers en the stochastic nature of the nanotubes distribution into a polymer matrix. Unless a special care is taken, in buckypaper nanocomposites, the ODF defines ori- the nanotubes are distributed randomly in buckypa- entation probability density and must result in a com- per sheets. To achieve certain alignment, buckypaper posite with overall isotropic properites, if CNTs are dis- sheets are produced by filtrating well-dispersed na- tributed randomly in buckypaper. ODF is dervied from notube suspension through a filter placed in a high the analysis of the SEM images of CNT buckypapers. strength magnetic field (Liang et al. 2003). A strong Analytical ODFs describing various microstructures are magnetic field (5–15 T) substantially improves align- also introduced. ment of CNTs and thereby increases the buckypaper’s It will be shown that the Mori-Tanaka scheme applied elastic modulus and strength in the direction of align- to the non-aligned CNT buckypaper polymer matrix ment. Moreover, alignment controls the elastic, ther- composites leads to violation of symmetry of the effec- mal, and electrical properties of buckypaper nanocom- tive elastic moduli tensor. posites. On the other hand, it is virtually impossible 332 Talks Topic K 1: Polymer based composites The study of the literature also reveals that there are References no known bounds derived for the composites with Liang, Z., Shankar, K.R., Barefield, K., Zhang, C., Kram- orientational distribution (except for the random uni- er, L., & Wang, B. (2004): Investigation of magneti- form distribution) of phases. To overcome this issue a cally aligned carbon nanotube bucky papers/epoxy problem of finding tightest bound for the composites composites. - In: Proceedings of SAMPE (48th ISSE). with non-aligned phases is formulated as a nonlinear Long Beach, CA, May, 2003. semidefinite optimization problem, i.e., an optimi- 4. Mori, T. & Tanaka, K. (1973): Average stress in ma- zation problem where the optimization variables are trix and average elastic energy of materials with represented by symmetric positive semidefinite matri- misfitting inclusions. - Acta Metall., 21: 571-574. ces. Such a formulation guarantees that any solution 8. Hashin, Z. & Shtrikman, S.A. (1963): Variational of the optimization problem represents a valid tensor approach to the theory of the elastic behaviour of of elastic material properties. The problem is solved by multi-phase materials. – J. Mech. Phys. Solids, 11: an interior point method, and an optimal solution pro- 127-140. duces bounds for the overall elastic properties of the multiphase composites with orientational distribution of phases. Estimataion of Dispersion Condition for PP/CNT Nano Com- posite by Using the New Segments with Extensional Flow for Co-Rotating Twin Scew Extruder Koki Matsumoto, Takayuki Morita, Yoshihiko Arao, Tatsuya Tanaka Mechanical Enginnering , Department of Science and Enginerring , Doshisha University, Kyoto, Japan Presently, nano composites, consisting of polymers Firstly, the pressure drop at the Blister Disk were that are reinforced with nano fillers, have been de- measured with fundamental extrusion equipment by veloped to obtain further mechanical properties and changing the geometries and volumetric flow rate. The further functionalities. However, intended properties dispersion is caused by stress magnitude and the ex- have not been achived properties because of nano fill- tensional stress can be expressed by entrance pressure er agglomerations in the polymer. Extensional flow has drop from Cogswell equation. Then, the dispersion been shown to be more efficient solution for improv- degree of extruded specimens was observed by mi- ing the dispersion of nano-composites as compared to croscopy and TEM. Moreover, as the other evaluation shear flow from Grace Curve. One of the production method of dispersibility, the rheology analysis with ro- processes of nano-composites is melt extrusion with tational viscometry and electric conductivity. Finally, co-rotating twin scew extruder (TSE) which is superi- these results were validated the tendency. From these or in terms of productivity and mixing performance. results, the critical Pressure value can be estimated However, it is difficult to disperse the fillers by conven- and the dispersibility of PP/CNT nano composites were tional processing (e.g. shear mixing flow with Kneading increased dramatically by extensional flow. Block). Therefore we attempt to disperse the fillers by using References new segments with elongational flow for twin screw Tokihisa, M., Yakemoto, K., Sakai, T., Utracki, L.A., extruder. This new segment is called “Blister Disk” Sephehr, M., Li, J. & Simard, Y. (2006): Extensional and it has many small holes on Disk. However, it was Flow Mixer for Polymer Nanocomposites – Polym. difficult to evaluate the mixing performance of Blis- Eng. Sci., 46: 1040-1050 ter Disk because the flow patterns are complex in TSE Cogswell, F.N. (1972): Conversing Flow of Polymer and there is some possibility of no flow through the Melts in Extrusion Dies – Polym. Eng. Sci., 12: 64-73 holes of Blister Disk. Then, to evaluate the disperion Grace, H.P. (1982): Dispersion Phenomena in High Vis- effect of only holes, fundamental extrusion equipment cosity Immiscible Fluid Systems and Application of was developed. Our objective is estimation the disper- Static Mixers as Dispersion Devices in Such Systems sion condition by changing the Blister Disk geometries – Chem. Eng. Comm., 14: 225-277 (e.g. hole numbers. hole diameter and hole width) in the case of polypropylene (PP) and Carbon Nano Tube (CNT) nano composite. 333 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Characterisation of graphene-reinforced nanocomposites: optical-microscopy analysis of spatial non-uniformity Osman Bayrak1, Mariana Ionita2, Emrah Demirci1, Vadim V. Silberschmidt1 1Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Leicestershire, UK 2University Politehnica of Bucharest, Advanced Polymer Materials Group, Romania In the last decade, graphene has emerged as one of In this study, samples of graphene oxide (GO)-alginate very promising reinforcement materials for nanocom- composites were studied based on a combination of posites. Apparently, it can outperform many other mechanical tests (tensile loading up to failure) and mi- known nano-reinforcements, improving properties crostructural characterisation using optical microscopy and performance of nanocomposites (Rafiee, 2009). (supported with TEM studies). Pull-outs of GO flakes As a field of study that is only a decade old, there are were compared quantitatively for nanocomposites still many features of such nanocomposites that need a with different volume fractions of nano-filler. The im- thorough analysis. One of them is the effect of their mi- ages obtained provided information that can contrib- crostructural characteristics and their spatial non-uni- ute to understanding of the mechanical behaviour of formity on deformation processes. To understand the analysed materials. The study will be extended to their mechanical behaviour, such characterisation is incorporate the obtained results into finite-element indispensable. Although many studies performed char- models. acterisation of graphene-reinforced nanocomposites with transmission or scanning electron microscopy, or References atomic force microscopy (Kuilla, 2010), these methods Rafiee MA, Rafiee J, Wang Z, Song HH, Yu ZZ, Korat- are rather time-consuming and cumbersome in inter- kar N. Enhanced Mechanical Properties of Nano- pretation of their results related to the macroscopic composites at Low Graphene Content. ACS Nano behaviour. Employment of optical microscopy, that is 2009;3(12):3884-3890. easy to implement compared to TEM, SEM and AFM, Kuilla T, Bhadra S, Yao DH, Kim NH, Bose S, Lee JH. Re- could simplify significantly characterization of nano- cent advances in graphene based polymer compos- composites and, hence, their performance. ites. Progress in Polymer Science 2010;35(11):1350- 1375. 334 Talks Topic K 2: Polymer based composites Talks Topic K 2: Polymer based composites 335 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Progressive damage evaluation of Glass-Epoxy laminated composites under fatigue loading Soran Hassanifard, Mohsen Feyzi Department of Mechanical Engineering, University of Tabriz, Iran Polymeric composite materials are widely used in many inforced laminates. In addition, this model can predict fields of industry due to the excellent specific strength, the modes of fatigue failure. The iterative algorithm good electrical resistance and high speed production. was used so that at each step of solution, maximum In the past five decades, the researchers have focused load was applied to the model and stresses were eval- on determining the fatigue life of these materials. uated. Then the appropriate failure criterion was ap- However, this phenomenon is not known completely. plied to inspect for possible failure in all layers of all There has been lots of research on the fatigue life esti- elements. For failed layer in an element, material prop- mation that can be classified in some strings. erties were modified according to the failure mode and Some of the works are available that define a damage progressive damage theory. In other elements that model in composite materials during fatigue failure were not failed, the damage parameter was calculat- process. In these studies, one of the mechanical prop- ed. If the value of the damage in each element exceeds erties are selected as damage variable and the changes 0.9, the layer of the element was assumed to be failed in this parameter are recorded within failure develop- and the algorithm was continued, then the fiber and ment. Finally, a damage function is fitted on experi- matrix failure in tension were analyzed. In addition, a mental data. Often, the dynamic modulus is chosen as new useful and simple model was presented to assess mentioned parameter (Giancane et al 2009). the changes in residual stiffness during fatigue proce- A number of investigators have proposed a fatigue dure. failure criterion based on components of stress ten- Also, to characterize the effect of stress ratio, the Ka- sor. They have replaced the static strengths in these wai’s failure criterion were applied, however this law theories by corresponding fatigue functions and then cannot recognizes the modes of failure. The predicted determined the fatigue cycles to failure. They formu- fatigue life was compared to the experimental results lated these criteria according to stresses that affect on available in the literature and good agreement was ob- the mode of failure (Hashin and Rotem 1973). In the served. aforementioned model, the effect of stress ratio has not been considered exactly and the model is limited to value of the stress ratio. Many investigations in lit- References erature have tried to develop a failure law to solve this Giancane, S., Panella, F.W. & Dattoma, V. (2009): Char- challenge. In a composite specimen the value of stress acterization of fatigue damage in long fiber epoxy ratio is not equal at different locations. Therefore, it composite laminates, International Journal of Fa- should be applied to the solution. A failure criterion tigue, No. 32, pp. 46-53. could be obtained based on phenomenological fatigue Hashin, Z. & Rotem, R. (1973): A Fatigue Failure Cri- ratio. If the strength versus life curves at different stress terion for Fiber-Reinforced Materials, J. Compos. ratios are normalized based on the phenomenological Mater., No. 7, pp. 448-464. equation, all curves with different stress ratios collapse Kawai, M. (2004): A phenomenological model for to a single curve (Kawai 2004). off-axis fatigue behavior of unidirectional polymer In the present study, a Finite Element (FE) model based matrix composites under different stress ratios, on Hashin’s failure criterion was developed to predict Journal of composites (Applied science and manu- fatigue life of (0,90,0,90)s, (90,0,90,0)s E-glass fiber re- facturing), No. 13, pp. 955-963. 336 Talks Topic K 2: Polymer based composites Experimental Investigation of Cold Forming of PC-Films and tensile bars using Optical Measurements Kai-Uwe Widany, Christian Dammann, Rolf Mahnken Chair of Eingineering Mechanics (LTM), University of Paderborn, Germany The alignment of polymer chains is a well known mi- Additionally, we propose a method for approximation crostructural evolution effect due to straining of poly- of the true stress-strain curves at the local material mers. This has a drastic influence on the macroscopic points. This method is aided by experimental investi- properties of the initially isotropic material. gations on tensile bars to gain knowledge about the In this work, cold forming is performed at room tem- evolution of volumetric strains. perature on a tensile testing machine. Polycarbonate films are examined in two loading phases. In the first References phase the specimen is loaded to induce anisotropy, Arruda, E. M. & Boyce, M. C. & Quintus-Bosz, H. and in the second phase it is re-loaded while the mate- (1993) – Effects of Initial Anisotropy on the Finite rial direction is varied. The investigations are support- Strain Deformation Behavior of Glassy Polymers, Int. ed by an optical measurement system to gain knowl- J. Plast., 9: 783-811 edge about the inhomogeneous behavior in the initial Dammann, C. & Caylak, I. & Mahnken, R. (2014) – Ex- loading phase and the about the anisotropic behavior perimental Investigation of PC-Films Using Optical in the re-loading phase. Two-dimensional strain con- Measurements, Intern. Polymer Processing, 29 (2): tours are obtained from the test data. 260-271 Failure processes of fiber reinforced composites under off-axis loading Christian Marotzke, Titus Feldmann BAM (Federal Institute for Materials Research & Testing), Mechanics of Polymers, Berlin, Germany In structural applications of fiber reinforced materi- off-axis angle of 30° only 12% of the initial inter fiber als the composite plies comprising the laminates are failure load is left. loaded by multiaxial stresses. Composite plies are very The fracture plane in off-axis tests naturally is loaded sensible against the loading angle because of their by a combination of normal and shear stresses. For highly anisotropic mechanical properties. Especially off-axis angles below 45° the failure is dominated by the strength strongly depends on the loading angle be- shear stresses parallel to the fibers while above 45° cause the strength of the fibers is several times higher it is dominated by stresses normal to the fibers. Frac- than the strength of matrix and interface. The elastic ture surfaces for off-axis angles lower than 45° show properties as well as the failure processes under multi- the typical shear cusps develop which become more axial loading can be studied by off-axis tests. However, and more pronounced with decreasing off-axis angle. in off-axis tests two different failure mechanisms occur, Even in case of epoxy matrices very high deformations this is, fiber fracture or inter fiber failure. Depending occur leading to extremely cliffy fracture surfaces of on the specimen geometry either one or the other fail- the matrix zones between the fibers. In contrast, the ure process can occur in case of small off-axis angle. fracture surfaces are rather flat in case of pure tensile Since the ultimate load depends on the geometry the stresses normal to the fibers. In any case the fiber-ma- test results have to be split into failure with and failure trix interface fails because the interface commonly is without fiber fracture. weaker than the pure matrix. A series of off-axis tests is performed for a carbon fiber A fracture mechanical analysis of the inter fiber failure reinforced epoxy resin with a fiber volume fraction of process is performed by finite element simulations. 55%. For the given specimen geometry pure inter fib- The energy release rate is calculated by using the vir- er failure occurs for off-axis angles larger than 6°. Due tual crack closure method. The model consists of a to the large fracture surface the strength of the spec- regular hexagonal 12-fiber array. In order to determine imens is very high for small angles. The failure stress the influence of the distance between the fibers the rapidly decreases with growing off-axis angle. At an fiber volume fraction is varied between 5% to 85%. The 337 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 analyses reveal a strong influence of the fiber content References on the fracture process. The results show that the total Marotzke C. Influence of the interface on the on the energy release rate increases during a large part of the strength of fiber reinforced polymers. Proceedings debonding process indicating an unstable crack prop- of the ECCM 14, Budapest, Hungary, 2010. agation. Correa E, Mantic V, París F. Numerical characterisation In addition to pure interface cracks the kinking of the of the fibre–matrix interface crack growth in com- cracks from the interface into the matrix at different posites under transverse positions is analysed. The results show a strongly var- Hobbiebrunken T., Hojo M., Adachi T., de Jong C., Fie- ying energy release rate for the cracks along on their dler B. Evaluation of interfacial strength in CF/epox- path to the neighbouring fibers. ies using FEM and in-situ experiments. Composites Part A 2006;37:2248–56. Marotzke, C. Feldmann, T. Failure of composites under transvers loading - a fracture mechanical approach. Proceedings of ECCM15, Venice, Italy, 2012. Analysis and Simulation of the Fatigue Behaviour of CFRP Laminates Janko Kreikemeier1, Lukas Geiger2 1German Aerospace Center, Structural Mechanics, Braunschweig, Germany 2 Karlsruhe Institute of Technology, Continuum Mechanics, Germany The simulation of the fatigue behaviour of carbon fibre The cyclic loading is taken into account via the cycle reinforced plastics (cfrp) is very complex and challeng- jump algorithm available in Abaqus. In this apporach, ing. Compared to isotropic materials, the experimental the material degradation of the structural response of characterization of cfrp materials suffers high costs. a single load cycle is extrapolated over a discrete num- Additonally, there exist many failure mechanisms ber of cycles to prevent the computation of every load which appear in parallel, i.e. fibre failure in tension and cycle. For this reason, periodic displacement functions compression, matrix failure in tension and compres- are utilized via Fourier series expansions. sion as well as delamination phenomena. The model is impelmented into the finite element sys- In the present work the constitutive model of (Govin- tem Abaqus via the User Material Subroutine utility djee, Kay, & Simo, 1995) is utilized to model the cfrp (UMAT). In conjunction with the cycle jump algorithm, fatigue behaviour. Originally developed for the de- this methodology is a powerful tool for the fatigue in- scription of concrete like structures, the model does vestigation of composite materials. not take into account failure mechanism caused by In addition, the constitutive characterization of the cfrp cyclic loading conditions. For this reason, the model is material under investigation is carried out by means of exploited to cycle dependence to capture the fatigue cyclic tension tests longitudinal as well as transverse to behaviour, as well. Both, the elastic constants as well the fibre direction following the standard DIN 527-5. as the strength values are degraded under cyclic load- The verification of the constitutive model via the sim- ing conditions. The static strength values used in the ulation of the cyclic tension tests and the comparison faiulure criterion are replaced by the residual stress with the experimental results revealed the suitability counterparts as function of the cycle number and the of the approach for the fatigue investigation of cfrp actual stress state. Thus, the corresponding function of materials. residual stresses is explicitely dependend on the static strength and the number of load cycles and implicitely References dependend on the actual stress state. For full descrip- Govindjee, S., Kay, G., & Simo, J. (1995). Anisotropic tion of the function, the Wöhler curve has to be known modelling and numerical simulation of brittle dam- from experiments. The approximation of the residual age in concrete. International Journal for Numerical stresses is necessary for all strength values, because Methods in Engineering 38 (21), S. 3611-3633. common failure criteria utilize numerous strength val- Tsai, S., & Wu, E. (1971). A general theory of strength ues for failure description. In this work, the non-differ- for aniostropic materials. Journal of Composite Ma- entiating Tsai-Wu failure criterion, (Tsai & Wu, 1971), is terials 5 (1), S. 58-80. used for description of the damage onset. 338 Talks Topic K 2: Polymer based composites Inline metrology of carbon fiber preforms as an indicator of mechanical properties of consolidated CFRP parts Daniel Brabandt, Gisela Lanza Karlsruhe Institute of Technology, wbk Institute of Production Science, Germany The material group of carbon fiber reinforced polymers specimens representing typical geometric features are (CFRP) is getting more important as a construction ma- investigated. Based on the generated data-sets which terial. Due to its high mechanical load capacity CFRP are represented by a cloud of points further analysis can be applied in many applications. The low density in can be performed. The data can help to improve the combination with its mechanical properties makes this manufacturing technologies within the preforming material predestinated for lightweight design. Due to process by getting a three dimensional model of the this CFRP are getting into the focus for the automotive preform. This model offers the opportunity to analyze serial production. But to establish them the production the macroscopic behavior of the semi-finished textile costs and the cycle times have to decrease significant in the forming operation. Furthermore the three di- (McKinsey & Company 2012). mensional model of the preform can be used as a vali- To facilitate a large-scale use the automated production dation for draping simulations. has to be further developed. Irrespective to the kind of In a direct link to the production process the imple- infiltration the forming operation of the semi-finished mentation of an inline metrology system will give the textiles is a significant process step that has to be con- possibility to evaluate deviations from given tolerance trolled. In the so called preforming process the two di- limits so that a quality judgment can be made at an mensional semi-finished textiles are laid up in several early stage. This leads to reduced production costs layers and are transformed into a three dimensional and scrap rates. The presented metrology system will near net shape geometry. Due to the anisotropic prop- also give an support to set the right tolerance limits. erties of carbon fibers this process is crucial for the fi- By digitalizing specimens with known defects a holistic nal mechanical properties of the consolidated part. approach for the evaluation of effects of defects (EoD) The complexity of the process makes it susceptible to will be possible by giving essential information to com- defects such as form deviations, folds and misalign- bine them with NTD and destructive end of line tests. ment of the textiles (Härtel & MIddendorf 2013). These deviations can lead to a significant loss of the References mechanical properties of the final part. Currently these McKinsey & Company (2012): Lightweight, heavy im- kinds of defects are typically detected in an end of pact – How carbon fiber and other lightweight ma- line quality inspection by using nondestructive testing terials will develop across industries and specifically (NDT) methods. Thus to get a holistic understanding of in automotive; Advanced Industries. the production process it is necessary to measure the Härtel F, Middendorf P. (2013): Preforming parame- preform directly after the preforming process (Lanza & ter studies and comparision of different preform Brabandt 2013). processes with NCF material. 19th International The objective of the presented approach is to gener- conference on composite materials ICCM19.. p. ate a complete surface measurement of the preform. 7577-7587. Therefor a triangulation system using laser stripe sen- Lanza G, Brabandt D. (2013): Design of a measure- sors is implemented on a three-axis-kinematics that ment machine for quality assurance of preforms in moves the sensors over the surface. It will be dis- the CFRP process chain. Apprimus Verlag,. Aachen. cussed what kind of specific challenges occur by meas- ISMTII 2013: Metrology - Master Global Challenges. uring carbon fiber preforms and how they are solved ISBN 978-3-863-59138-0. by the presented setup. As a reference carbon fiber 339 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Characterization of complexly warped components made from locally reinforced UD-tape laminates BENJAMIN HANGS1, TOBIAS LINK1 , FRANK HENNING1,2 1Fraunhofer-Institut for Chemical Technology (ICT), Pfinztal, Germany 2Karlsruhe Institut of Technology (KIT), Institute for Vehicle System Technology (FAST), Germany In the past decades significant research has been con- symmetric layup results for the patched section which ducted with regard to efficient processing of thermo- causes the coupon to warp. The coupon is illustrated plastic advanced composites. One aspect, out of a in Figure 1. wide variety, is the formation of thermal stresses in the course of the cooling stage. The main cause for this effect is the highly anisotropic material behavior of continuous fiber-reinforced thermoplastics. In par- ticular, the significantly different coefficients of ther- mal expansion (CTE) of polymer matrix and reinforcing fibers [1]. From a process perspective, balanced thermal stresses Fig. 1: Illustration of the investigated coupon within a symmetric laminate are not necessarily criti- cal. By contrast, unbalanced thermal stresses, especial- ly in thin walled components, result in significant shape To characterize the complex deformation modes deformation leading to difficult or even impossible which result from the locally unsymmetric layups, it assembly. Two main aspects exist which create unbal- is essential to have an accurate geometric dataset anced thermal stresses across a laminate’s cross-sec- representing the warped coupons. Within this study a tion. First are process related disturbace variables such hand-operated laser scanner is used to generate pre- as cooling gradients, tool-part interaction and others. cise 3D point clouds of the physical components. This In addition, unsymmetric layup design is a key driver data is then post-processed with the aim to analyze [2]. Although the latter is ultimately avoidable, this the types of warpage for the different layups and kind of layup design is of interest for creating highly to determine its quantity. Based on these findings, tailored components with locally reinforcing materi- parameters are derived which allow to compare and al along the main load paths. Automated tape-laying categorize the different deformation modes observed. technologies nowadays provide the possiblity to create such tailored layups with the required accuracy. References This presentation deals with the layup-induced war- Nairn J.A., Zoller P.; Matrix solidification and the re- page of tailored laminates made from UD-tape. For sulting residual thermal stresses in composites, this purpose, rectangular CF/PPS laminates (baseplate Journal of Material Science 20 (1985) p. 355-367 G) with a centered, longitudinal reinforcement patch Hyer M.W.; Some Observations on the cured shape of (P) are produced with a wide variety of layup combina- thin unsymmetric laminates, Journal of Composite tions for G and P. The baseplate as well as the patch are Materials 15 (1981) p. 175-194 designed as symmetric layups. In consequence an un- 340 Talks Topic K 3: Polymer based composites Talks Topic K 3: Polymer based composites 341 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 RVE modeling of fibre-reinforced-polymer curing coupled to visco-elasticity CHRISTIAN DAMMANN, ROLF MAHNKEN Chair of Eingineering Mechanics (LTM), University of Paderborn, Germany Our work concentrates on the mesoscopic constitu- ical loading, while thermal loading is handled homog- tive model for temperature-dependent visco–elastic enously on the mesoscale. Homogenization leads to effects accompanied by curing, which are important results on the less resolved macroscale. phenomena in production processes of intrinsic hy- In the examples we illustrate the characteristic behav- brids. These integral components are hybridized in a ior of the model, such as shrinking due to curing and modified resin transfer molding process adding e.g. temperature dependence and simulate the hybridiza- steel as a second semi-finished product to the textile. tion process as well as mechanical loading of the cured During hybridization and later mechanical loading, the part with the finite-element-method. Results from the periodic microstructure defined by resin and fibers is mesoscale are compared with those of the macroscale. taken into account as a representative unit cell (RVE) subjected to thermo-mechanical loading. Acknowledgements The polymeric resin component is modeled using an This work is based on investigations of the „SPP 1712 approach from Mahnken (2013), where an additive ter- - Intrinsische Hy-bridverbunde für Leichtbautragstruk- nary decomposition of the logarithmic Hencky strain turen”, which is kindly supported by the Deutsche tensor into mechanical, thermal and chemical parts For-schungsgemeinschaft (DFG). is used. Based on the concept of stoichiometric mass fractions for resin, curing agent and solidified material References the bulk compression modulus as well as the bulk heat- Mahnken, R. (2013): Thermodynamic consistent mod- and shrinking dilatation coefficients are derived and eling of polymer curing coupled to visco-elasticity compared with ad hoc assumptions from the literature at large strains – International Journal of Solids and Halley & Macackay (1996), Lion & Höfer (2007). More- Structures, 50: 2003-2021. over, we use the amount of heat generated during dif- Halley, P.J. & Macackay, M.E. (1996): Chemorheology ferential scanning calorimetry until completion of the of thermosets, an overview - Polymer Engineering chemical reactions, to define the chemical energy. As a and Sciences, 36(5): 593-609. major result, the resulting latent heat of curing occur- Lion, A. & Höfer, P. (2007): On the phenomenological ring in the heat-conduction equation derived in our ap- representation of curing phenomena in contiuum proach reveals an ad hoc approach from Hilton (2003) mechanics - Archive of Mechanics, 59: 59-89. as a special case. Hilton, H.H. (2003): Optimum viscoelastic designer Linear elastic fibers in addition with the resin are used materials for minimizing failure probabilities during to model an RVE on the mesoscale. Periodic boundary composite curing - Journal of Thermal Stresses, 26: conditions for displacements are applied including a 547-557. macrostrain from the upper scale, to describe mechan- Characterization and simulation of the time-dependent an- isotropic deformation behaviour of continuously reinforced PA6 material Andreas Roesner, Luise Kaerger, Frank Henning Karlsruhe Institute of Technology, Institute for Vehicle System Technology, Germany The mass production of continuously reinforced com- be reshaped after manfacturing and can be recycled posites is a challenge that has not been finally solved. after lifetime. Because of these positive characteristics Composites with thermoplastic matrix systems offer continuously reinforced thermoplastics are an attrac- relatively short cycle times and easy handling. Due to tive alternative for the use in structural applications. the capability of thermoplastic matrices to melt again However, it is not yet fully understood how the after initial consolidation, the composite material can time-dependent viscoelastic-viscoplastic deformation 342 Talks Topic K 3: Polymer based composites behaviour of the isotropic thermoplastic matrix is trix is incoporated that shows viscoelastic, as well as transfered to the orthotropic, continuously reinforced plastic behavior, in order to analyse whether plastic composite. As a consequence, there is still a lack of deformation can be neglected or need to be consid- suitable material models for describing the macroscop- ered in a homogenized, macroscopic material model. ic, time-dependent and directional material behaviour As proposed by Garnich & Karami (2004), who assume of said composites. Considering the carbon fiber rein- purely elastic behavior of the constituents, wavy unit forced polyamide 6 material presented in this work the cells are used to study the time-dependent behavior aspect of fiber waviness has to be taken into account. under tension and compression depending on the apli- Depending on the geometry of the part and the chosen tude to wavelength ratio. It is shown that triaxial strain process parameters, fiber waviness may occur in rather states significantly influence the time dependence and large areas of the composite part. The carbon fibre PA6 that fibre waviness leads to asymmetric stiffness as tapes are processed through heating above melt tem- well as creep compliance under tension and compres- perature, shaping and lastly cooling of the shaped part. sion. During cooling the matrix shrinks considerably due to Based on the micromechnical unit cell model, a threed- crystallization while the carbon fibers elongate slightly imensional macromechanical model is proposed that due to a moderatly negative thermal expansion coef- adequately represents the time-dependent, direction- ficient. Hence, the carbon fibres are compressed and al behavior of the investigated unidirectional carbon wrinkle due to their extreme slenderness. This leads fibre PA6 material. to a significant decrease in axial stiffness depending on the amplitude to wavelength ratio of the wavy fibers Reference (Garnich & Karami 2004). Garnich, M. & Karami, G. (2004): Finite Element Mi- This work presents a numerical characterization of the cromechanics for Stiffness and Strength of Wavy time-dependent deformation behavior of the unidirec- Fiber Composites. – In: Journal of Composite Mate- tional carbon fiber PA6 material using representative rials, Vol. 38, No.4 2004. volume elements (RVE). A material model for the ma- Topological Interlocking Materials - Towards New Polymeric Hybrid Materials Lee Djumas, Andrey Molotnikov, George P.Simon, Yuri Estrin Department of Materials Engineering, Monash University, Clayton, Australia Composites play an important role as structural mate- can withstand flexural deflections ten times larger than rials in a broad range of fields due to the potential to those of a solid plate of the same thickness from the combine beneficial properties of their constituents. In same material (Krause et al., 2012). It is anticipated Nature, composites display fascinating architectures at that hybrid materials obtained by adding a soft phase multiple length scales, each of which can influence dif- to assemblies of topologically interlocked blocks will ferent properties. They are increasingly being used as have superior mechanical properties. inspiration to develop novel materials. One particular With the aid of additive manufacturing, which has principle of interest is the combination of hard building gained much attention due to its broad and far reach- blocks, that constitute a majority phase, and a soft ma- ing potential applications, we are granted further de- trix phase, thus mimicking the microstructure of nacre, sign freedom allowing fabrication of complex geom- with its exceptional fracture toughness (Meyers et al., etries with fine features at micrometre resolutions. 2014). Employing the latest state of the art 3D printing tech- In this work we present a geometrical concept known nology as a simple and efficient rapid manufacturing as topological interlocking (Estrin et al., 2011), which technique, we are able to print multiple polymeric can be utilised to vary the geometry of the hard build- materials with intricate inner architectures and wide- ing blocks and potentially produce structures with im- ly contrasting mechanical properties within the same proved properties compared to traditional platelet-like build. As a result, the ability to develop and investigate blocks. The concept of topological interlocking is based complex polymer composite assemblies, based upon on periodic assemblies of identical, discrete elements the two design principles - topological interlocking and with specifically designed geometries where each mimicking nacre - has become highly viable. block is held kinematically in place by its neighbours. In this talk we will present a combination of results Our previous investigations have demonstrated that detailing the experimental and computational model- a plate segmented into interlocked ceramic elements ling work done to develop and fabricate multi-material 343 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 topologically interlocked structures using 3D-printing Estrin, Y., A.V. Dyskin, and E. Pasternak (2011), Top- techniques. Preliminary work on multi-phase assem- ological interlocking as a material design concept. blies motivated by nacre structures will also be pre- Materials Science and Engineering C, 31, pp. 1189- sented. 1194. Krause, T., Molotnikov, A., Carlesso, M., Rente, J., References Rezwan, K., Estrin, Y., Koch, D. (2012), Mechanical Meyers, M. A., and Chen, P.-Y. (2014), Biological Ma- Properties of Topologically Interlocked Structures terials Science: Biological Materials, Bioinspired with Elements Produced by Freeze Gelation of Ce- Materials, and Biomaterials, Cambidge University ramic Slurries, Advanced Engineering Materials 14, Press. pp. 335-341. Homogenisation of thermoelastic properties of short-fibre reinforced polymers and validation based on experimental characterisation L. Kehrer, V. Müller, B. Brylka, T. Böhlke Chair for Continuum Mechanics, Institute of Engineering Mechanics, Karlsruhe Institute of Technology (KIT), Ger- many Polymer based composites are increasingly applied as interaction direct derivative (IDD) estimate developed lightweight material in various fields due to their ad- by Zheng and Du (2001). Based on the three-phase vantageous material properties. Short-fibre reinforced model, cf., e.g., Christensen and Lo (1979), the IDD thermoplastics provide additionally advantages con- estimate considers interaction between fibres and the cerning fabrication by injection moulding and recy- surrounding matrix material and the fibre distribution. cling. The fabrication process, however, influences the The mean field homogenisation with the IDD approach properties of the microstructure. Introduced local fibre is performed by means of micro-computed tomogra- orientation distribution, spatial distribution, and vari- phy data describing the microstructure of the com- ation in geometry of the fibres, e.g., cause inhomoge- posite, cf., Müller et al. (2014). For the application of neous and anisotropic mechanical material behaviour. the homogenisation scheme, experimental data of the During the injection moulding process, cooling rates polypropylene matrix obtained by the DMA are used lead to effects on the microstructure of the compos- as input parameters. The effective properties of the ite, cf., e.g., McGonigle et al. (1999) and Meister et al. composite, resulting from numerical homogenisation (2012). These structures are not balanced and exhib- with the IDD scheme, are compared to experimental it post-crystallisation effects. The original amorphous results for various time-temperature loading histories structures can be restored by an increase of tempera- as well as to homogenisation results by means of the ture. Especially in case of semi-crystalline thermoplas- self-consistent method. The results of both homogeni- tics, the stiffness depends on the degree of crystalli- sation methods qualitatively represent the tempera- sation, which is linked to temperature and time. Thus, ture-dependent material behaviour. However, the IDD the degree of crystallisation affects the mechanical estimate is closer to the experimental results than the properties. In addition to the anisotropic and inho- self-consistent approximation. mogeneous material behaviour, the effective stiffness properties depend further on temperature and strain- References rate and are coupled to temperature history. Müller, V., Brylka, B., Dillenberg, F., Glöckner, R., By means of dynamic mechanical analysis (DMA), Kolling, S., Böhlke, T. (submitted 2014): Homogeni- material properties of polypropylene as well as fibre zation of Elastic Properties of Short Fiber-reinforced reinforced polypropylene are investigated by tensile Composites Based on Measured Microstructure tests under thermal loading. The impact of crystallin- Data. ity on viscoelasticity of the matrix material is analysed. McGonigle, E. A., Daly, J. H., Gallagher, S., Jenkins, The thermal loading is varied in a range of -50°C and S. D., Liggat, J. J., Olsson, I., Pethrick, R. A. (1999): 120°C. Changes of mechanical material properties of Physical Ageing in Poly(ethylene terephthalate) - its the experimental data by thermal loading history are Influence on cold Crystallization. – In: Polymer, 40: discussed. 4977-4982. The effective thermoelastic material behaviour of the Meister, S., Jungmeier, A., Drummer, D. (2012): Long- fibre reinforced composite is modelled by use of the Term Properties of Injection-Molded Micro-Parts: 344 Talks Topic K 3: Polymer based composites Influence of Part Dimensions and Cooling Condi- sion distribution. – In: Journal of the Mechanics and tions on Ageing Behavior. – In: Macromolecular Physics of Solids, 49: 2765-2788. Materials and Engineering, 297: 994-1004. Christensen, R. M., Lo, K. H., (1979): Solutions for ef- Zheng, Q.-S., Du, D.-X. (2001): An explicit and univer- fective shear properties in three phase sphere and sally applicable estimate for the effective properties cylinder models. – In: Journal of the Mechanics and of multiphase composites which accounts for inclu- Physics of Solids, 27: 315-330. Phenomenological characterization and macromechnical modeling of anisotropic, non-linear behavior of sheet mold- ing compounds (SMC) Marina Mrkonjić1, Ute Rayling2, Kay André Weidenmann3, Luise Kärger4, Frank Henning5 1,2,4 Karlsruhe Institute of Technology (KIT), Institute of Vehicle System Technology (FAST), Department of Lightweight Technology (LBT), Germany 2now: French-German Research Institute of Saint-Louis, Advanced Materials Technologies, Saint-Louis, France 3Karlsruhe Institute of Technology (KIT), Institute for Applied Materials IAM-WK, Germany 5Fraunhofer Institute for Chemical Technology (ICT), Polymer Engineering (PE), Pfinztal, Germany The present work deals with anisotropic and non-line- considered to be time-independent, irreversible and ar effects in the mechanical behavior of sheet molding dependent on the maximum stress state, causing stiff- compounds (SMC) as a viscoelastic damageable mate- ness degradation with increasing strain. The anisotrop- rial. ic elastic damage theory by Chow and Wang is used SMC, as a long fiber reinforced thermoset primarily (Chow & Wang, 1987). Material failure can be predict- produced by compression molding, is considerably af- ed by one of the tensor-polynomial failure theories fected by the processing parameters resulting in aniso- that are implemented in the FE-code. tropic material properties. Local inhomogenities may Finally, a comparison of simulation and experimental also occur. results is presented, showing good accordance be- Different macroscopic measurements have been em- tween the stress-strain-curves, thus validating the ployed to determine the material parameters needed model. for modeling. For the characterization of non-linear ef- fects, cyclic test procedures are developed. In the early References stages of the SMC deformation, damage mechanisms Oldenbo, M. (2004): Anisotropy and non-linear effects and viscoelasticity occur simultaneously. in SMC composites from material data to FE-simu- A constitutive model for the macromechanical lation of structures, Lulea University of Technology, simulation of anisotropic SMC is implemented in Diss. the FE software ABAQUS. Assuming that dam- Chow, C.L. & Wang, J. (1987): An anisotropic theory of age mechanisms and viscoelastic effects can be elasticity for continuum damage mechanics, Inter- decoupled (Oldenbo 2004), the two effects are national Journal of fracture 33:3-16; Dordrecht. analyzed individually. The damage evolution is 345 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic L 1: Lightweight alloys and structures 346 Talks Topic L 1: Lightweight alloys and structures Mechanical properties and microstructure of Ti6Al4V fabri- cated by selective laser melting Radomila Konecna1, Gianni nicoletto2, Adrian Baca1, Ludvik kunz3 1University of Zilina, Zilina, Slovakia 2University of Parma, Parma, Italy 3Institute of Physics of Materials, Brno, Czech Republic Selective Laser Melting (SLM) is one of the emerging Light and scanning electron microscopy were applied technologies in the broad area of Additive Manufac- to reveal the microstructure. turing (AM). In SLM method the metal powder is se- It has been found that the ultimate tensile strength lectively melted layer-by-layer by a computer driven and elongation depends on the layer-by-layer building concentrated laser beam (Levy 2010). The solidified orientation of the specimen gauge length. The studied material progressively generates a part of any complex alloy Ti6Al4V prepared by SLM is a typical two phase 3D shape thus minimizing the need for material remov- α+β structure containing α and β phases which are sta- al, (e.g. by means of milling and drilling) (Kahlen & Kar bilized by alloying elements. The HIP process improved 2011). porosity and density of the specimens and affected the The SLM process is characterized by the generation of structure, too. The microstructure consists of a lamel- complex microstructure and a residual stress system, lar structure of α+β phases. During the SLM process which depend on the laser path, laser energy and α´ martensite is formed. The subsequent HIP process speed, solidification rate and the other parameters of converted the original structure into a lamellar α+β this advanced technology. The process is capable of structure. producing an almost fully dense material, although hot During the tensile tests the digital image correlation isostatic pressing at high temperature is often used to (DIC) technique was used to determine and monitor further improve the ductility and toughness. However, the full field strain distributions. The heterogeneous the relative novelty and the complexity of the process- nature of the strain and damage accumulation with- ing/ microstructure and properties relationships make in the material microstructure was observed and dis- SLM a manufacturing technology requiring further de- cussed. The severe strain gradients determined by DIC tailed investigation, focussed on relations among mi- were then verified by micro hardness mapping of the crostructure, mechanical properties and the parame- microstructure. ters of the manufacturing process. The applied DIC technique enables to determine the This study is aimed on an examination of relationships degree of material anisotropy in tensile specimens among mechanical properties and microstructure of fabricated from Ti6Al4V alloy. The strain heterogeneity Ti6Al4V alloy produced by SLM and the fabrication pa- is an index of expected scatter in microstructure-sen- rameters. SLM process was followed by a hot isostatic sitive mechanical properties, which are crucial for the pressing (HIP) treatment of the final product to obtain safe application of this manufacturing technology in fully dense material of high quality. view of the ready-to-use characteristics of the SLM Flat specimens with cross-section 6.25 x 4 mm for ten- parts e.g. in the demanding aerospace and biomedical sile tests were manufactured using a Renishaw A250 fields (Hollander et all 2006). system which operates with an Ytterbium fiber laser with a wavelength of 1075 nm. The source material for References SLM procedure was in the form of atomized titanium Levy, G.V. (2010): The role and future of the Laser powder with a granulometry in the range 15-45 µm. Technology in the Additive Manufacturing environ- Tensile specimens with two different orientations of ment. Physics Procedia 5, 65-80. layer-by-layer building were prepared. Displacement Kahlen, F. J. & Kar, A. (2011): J. Manuf. Sci. Eng. 123, controlled tensile tests with the rate of 0.001 mm/s 38. were conducted. An analysis of microstructure was Hollander, D. A., von Walter, M., Wirtz, T., Sellei, R. performed on metallographic specimens extracted Schmidt-Rohlfing, B., Paar, O., Erli, H.-J. (2006): Bio- from the gauge length of the tensile bars after testing. materials 27, 955. 347 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Formation of Twin Bands and Inhomogeneous Deformation in Mg-wrought Alloy AZ31 During Tension-Compression or Bending Loading K. Anten, A. Liehr, B. Scholtes University of Kassel, Institute of Materials Engineering – Metallic Materials, Germany Sheets of wrought Mg-alloy AZ31 exhibit a pronounced have been applied. In particular the development and rolling texture with basal planes preferably oriented disappearance of bands is investigated in case of cyclic parallel to the sheet plane. Due to this preferred ori- plastic deformation. The studies have shown that even entation of the hexagonal elementary cells, the domi- within the bands, a characteristic inhomogeneity of nant deformation mechanism – twinning or dislocation deformation exists and that, depending on the loading glide – depends on the loading direction regarding the condition, in the low cycle fatigue regime, inhomoge- crystallite orientation. This results in a pronounced neous deformation persists until fracture. asymmetry of the deformation behavior under tension or compression loading of AZ31 sheet material. In ad- References dition the formation of individual deformation bands Hazeli, K.; Cuadra, J.; Vanniamparambil, P.A.; Kontsos, with a higher twinning density compared to adjacent A. (2013), Scripta Materialia 68, S. 83–86. areas has been observed, leading to a pronounced in- Liehr, Alexander; Anten, K.; Scholtes, B. (2014), In: homogeneity of deformation (Hazeli et al. 2013; Liehr et Fortschritte in der Werkstoffprüfung für Forschung al. 2014). In this paper the formation and propagation und Praxis: Werkstoffeinsatz, Qualitätssicherung of deformation bands and their microstructure is stud- und Schadensanalyse, Hrsg. Wolfgang Grellmann ied in detail for tension-compression loading as well as und Holger Frenz. Deutscher Verband für Material- for bending loading. Optical as well as X-ray methods forschung und -prüfung e.V. Berlin Electrochemical-based characterization of the corro- sion fatigue behavior of creep-resistant magnesium alloy DieMag422 Martin Klein, Philipp Wittke, Frank Walther TU Dortmund University, Department of Materials Test Engineering (WPT), Germany Magnesium alloys offer a high potential for lightweight were correlated with corrosion properties of the alloy, construction, e.g. in automotive applications. However which were evaluated in potentiodynamic polarization their application range is limited due to their low cor- measurements and instrumented immersion tests. rosion resistance. Concurrently, corrosion- and deformation-induced mi- In the present study the influence of corrosion on the crostructural changes were observed by light and scan- microstructure and the depending mechanical proper- ning electron microscopy, yielding at a mathematical ties under cyclic loading of the newly developed, creep description of structure-property relationship. resistant magnesium alloy DieMag422 (Mg-4Al-2Ba- In the corrosion fatigue tests a significant reduction of 2Ca) was investigated. The corrosion fatigue behavior the corrosion fatigue strength with increasing corrosion was characterized in distilled water and sodium chlo- impact of the environments was determined, which ride solutions as well as under simultaneous anodic could be quantitatively correlated with the respective polarization. In this context, fatigue properties were corrosion rates. Plastic strain amplitude and deforma- estimated in load increase tests, using plastic strain tion-induced changes in electrochemical measurands and electrochemical measurements, and afterwards could be equivalently applied for a precise corrosion validated in constant amplitude tests. These results fatigue assessment. 348 Talks Topic L 1: Lightweight alloys and structures Very High Cycle Fatigue (VHCF) Assessment of Selective Laser Melted (SLMed) AlSi12 Alloy Shafaqat Siddique, Frank Walther Department of Materials Test Engineering (WPT) TU Dortmund University, Germany Selective laser melting (SLM) is a novel technique in ad- economical test procedure to determine the optimized ditive manufacturing which uses laser energy to melt set of process parameters on the basis of combined the powder material according to the geometry of the multiple step tests and constant amplitude tests. HCF computer aided design (CAD) model provided to the tests were carried out employing servohydraulic test SLM system. The manufacturing process employs lay- system, and the VHCF investigations were performed er-wise build-up of the part by melting powder mate- using an ultrasonic fatigue (USF) testing system. Be- rial. The process is specifically suitable for complex ge- sides, optical and scanning electron microscopes were ometries and customized parts which otherwise would used for microstructural and fracture analysis. The be costly and, even, impossible to be manufactured us- results show that there is a considerable influence of ing conventional manufacturing processes. This study process parameters and post-build heat treatment on aims at determining the high cycle fatigue (HCF) as well the fatigue performance. HCF and VHCF performance as very high cycle fatigue (VHCF) behavior of AlSi al- of SLM manufactured parts is, at least, comparable to loy manufactured by the SLM process. Different sets of that of conventionally manufactured alloys, and can be process parameters, along with post-build heat treat- further improved by carefully selecting the set of pro- ment, have been analyzed and fatigue characterization cess and post-process parameters. A microstructure- has been carried out to determine the effect of SLM and mechanism-based analysis has been carried out process parameters on HCF and VHCF behavior of AlSi for property-optimized manufacturing. alloy. Fatigue assessment has been carried out using an Formability Enhancement of 7075 Al Sheet with Two Step Forming Yong-Nam Kwon, Young Seon Lee Korea Institute of Materials Science, Changwon, Korea As the automotive industry has kept seeking the lighter ing has been applied to form complicated shape with car body, Al alloys became the most practical solution fine grained sheet. However, superplastic blow form- for weight reduction of automotive components. It ing with slow production cycle cannot be an adequate has become very easy to find various Al parts in every solution for large volume productions like automotive section of car body, such as hoods, doors, and chas- industry. Also, conventional Al alloy sheets with large sis. However, Al alloys did not replace every steel part and pan-caked grain structure cannot be a solution for currently in use. This comes not only from higher cost gas blow forming that requires low flow stress level at of Al compared to steel but also from a relatively infe- the elevated temperatures. We have designed the two rior formability especially in sheet. Usually, it has been step forming in which Al sheet was drawn to a kind of known that Al sheet formability reached only 2/3 of preform step following gas blow forming for accurate steel sheet at room temperature. Even though devel- geometry. In order to judge a formability enhancement opment of new Al alloys with higher formability would of Al sheet in terms of forming process, model geom- be the most desirable goal to expand Al alloy applica- etry came from a practical automotive part which had tion for lighter weight car, the new forming process to quite depth with complicated curvatures. The optimum best use of Al formability now available would be an- forming conditions for respective forming steps were other way to increase Al usage for weight reduction. considered most important technical features of this In the present study, two step forming comprised of process and would be discussed in details. Also, the mechanical and gas blow forming was investigated to effort to avoid detrimental microstructure evolutions fabricate automotive part having a complicated shape was given and discussed for a practical application. using Al 7075 alloy with a conventional formability which has been known to be quite lower compared Reference to deep drawing steels. Usual Al sheet forming con- Blair Carlson, etc. Challenges and opportunities rela- sists of several steps of forming, sometimes with the tive to increased usage of aluminum within the au- use of heated dies. Also, superplastic gas blow form- tomotive industry, TMS2010 meeting, TMS. 349 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic L 2: Lightweight alloys and structures 350 Talks Topic L 2: Lightweight alloys and structures Effect of Missing Cells on the Initial Stiffness and Plastic Yielding Surface of Three-Dimensional Micro-Lattice Struc- tures Kuniharu Ushijima1, Dai-Heng Chen2, Wesley James Cantwell3 1Tokyo University of Science, Tokyo, Japan 2Jiantsu University, Zhenjiang, China 3Khalifa University of Science, Abu Dhabi, UAE Over the decades, cellular materials such as two-di- In this study, the effects of cell geometry on the initial mensional honeycombs, three-dimensional foams and stiffness and plastic yielding surface of three-dimen- lattice materials have been investigated and developed sional lattice materials with defect have been studied as load-carrying by many researchers owing to their su- by using finite element method. In particular, emphasis perior mechanical properties per unit volume(Gibson is placed on predicting the yielding surface of lattice & Ashby, 1997). materials subjected to biaxial loading. The authors have been also studied on the mechanical This study can be a foundation for detecting the frac- behaviour of three-dimensional lattice blocks which tured cell walls in a lattice plate from the stiffness. Also, can be manufactured by selective laser metal sintering the effectiveness and ineffectiveness of introducing technique under uniaxial compression and shear load- the missing cell region on the mechanical properties ings(Ushijima et al., 2013). One of co-authors have de- per unit mass for lattice structures can be clarified. veloped the selective laser melting (SLM) technique for manufacturing micro-lattice structures at length scales References of microns(Tsupanos et al. 2010). Gibson L.J. & Ashby, M.F. (1997): Material properties The wide variety of mechanical response can be in “Cellular Solids: Structure and Properties”, 2nd achieved by changing the geometry of micro-architec- ed. Cambridge, Cambridge Press: 52-92. ture. Ushijima, K., Cantwell W.J, Chen, D.H. (2013): Predic- The behaviour of intact and damaged cellular materials tion of the Mechanical Properties of Micro-Lattice have been also investigated by some researchers up to Structures Subjected to Multi-Axial Loading, Inter- now. It can be anticipated that the behaviour is differ- national Journal of Mechanical Science, 68: 47-55. ent from that for conventional continuum materials. Tsupanos S., Mines, R.A.W., McKown, S., Shen, For example, Guo and Gibson have investigated the Y., Cantwell, W.J., Brooks, W., & Sutcliffe, C.J. Young’s moduli, elastic buckling strength and plastic (2010): The Influence of Processing Parameters yield strength of regular honeycombs with defects con- on the Mechanical Properties of Selectively La- sisting of missing cells based on finite element analysis. ser Melted Micro-Lattice Structures, Journal of Also, Chen et al. have studied the effect of geometrical manufacturing Science Engineering (ASME) 32: imperfection on the plastic yielding of two-dimension- DOI:10.11.15/1.4001743 al foams subjected to biaxial loading. High-strength microarchitected cellular materials: The interplay of design and size-dependent strength- ening Jens Bauer, Oliver Kraft1 Karlsruhe Institute of Technology, Germany Light materials are weak and strong materials are in the range of 1 g/cm3, only porous materials such as heavy, strength and density are generally considered as technical foams may reach considerably lower values strongly coupled. However, microarchitected cellular (Gibson & Ashby 1997). Although successfully used materials offer the opportunity to overcome that long in various lightweight components the mechanical standing barrier on the search for light yet strong properties of such cellular solids are limited by their materials. The lightest bulk materials have a density characteristic stochastic architecture (Fleck et al. 351 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 2010). Certain natural cellular materials such as bone, with different topological designs under several load on the other hand, remain strong since they have cases is shown. Optimization approaches of topology an optimized architecture and their basic material and shape with the aim to further enhance strength- is hierarchically structured, actually consisting of to-weight ratios are discussed. nanometer-size building blocks, providing enhanced material strength because of mechanical size-effects References (Gao et al. 2003). Gibson, L. J. & Ashby, M. F. (1997) Cellular Solids: It has been shown that high-strength cellular materials Structure and properties.. with specifically designed micro-architecture can be Fleck, N. A., Deshpande, V. S. & Ashby, M. F. (2010) fabricated artificially, applying 3D direct laser writing Micro-architectured materials: past, present and and atomic layer deposition. The resulting truss future. Proc. R. Soc. A Math. Phys. Eng. Sci. 466, structures consist of polymer beams with a typical 2495–2516. diameter of 0.5-1.0 µm coated with thin alumina Gao, H., Ji, B., Jaeger, I. L., Arzt, E. & Fratzl, P. (2003) layers. The conjunction of both structural design and Materials become insensitive to flaws at nanoscale: size dependent material strengthening effects enables Lesson from nature. Proc Natl Acad Sci USA 100, outstanding ratios of strength to weight. (Bauer et al. 5597–5600. 2014) Bauer, J., Hengsbach, S., Tesari, I., Schwaiger, R. & In this paper we present an overview of the mechanical Kraft, O. (2014) High-strength cellular ceramic com- properties of such micro-structured cellular materials. posites with 3D microarchitecture. Proc Natl Acad The interplay of size-dependent strengthening effects Sci USA 111, 2453–2458. Self-assembled ultra high strength, ultra stiff mechanical metamaterials based on inverse opals Gerold A. Schneider1,, Jefferson J. do Rosário1, Erica T. Lilleodden1,2, Martin Waleczek3, Roman Kubrin1, Alexander Yu. Petrov4, Pavel N. Dyachenko4, Julian E.C. Sabisch2, Kornelius Nielsch3, Nor- bert Huber2, Manfred Eich3 1Institute of Advanced Ceramics, Hamburg University of Technology, Hamburg, Germany 2Institute of Materials Research, Materials Mechanics, Helmholtz-Zentrum Geesthacht, Geesthacht, Germany 3Institute of Nanostructure and Solid State Physics, Universität Hamburg, Jungiusstrasse 11, 20355, Hamburg, Germany 4Institute of Optical and Electronic Materials, Hamburg University of Technology, Hamburg, Germany Inverse opals are known metamaterials in the field of and elastic modulus of 1.7 to 7.5 GPa as measured by photonics, being able to effect the propagation of light. uniaxial compression of micro-pillars. Simulations have In this work, we present the inverse opal structure not shown that these properties arise from a nearly homo- as a photonic metamaterial but explore its design as a geneous distribution of stresses in the structure. The mechanical metamaterial. Silica and titania coated sili- results suggest that inverse opals open new possibili- ca structures with densities in the range of 330-910 kg/ ties of design for lightweight structures with enhanced m3 resulted in unexpected strengths of 48 to 336 MPa mechanical properties. An efficient analysis model for the stresses in arbitrary adhesive lap joints with flat laminated adherends Nicolas Stein, Philipp Weissgraeber, Wilfried Becker Institute of Structural Mechanics, TU Darmstadt, Germany With the growing demand for lightweight construc- nents with dissimilar materials. This is of special in- tions adhesive joints are increasingly used in industrial terest with regard to the widespread use of fibre rein- applications. One of the major advantages of adhesive forced plastics (FRP). However, the knowledge of the bonding is that it enables to join thin-walled compo- load transfer and stress distribution in the adhesive 352 Talks Topic L 2: Lightweight alloys and structures joint is crucial for the design of engineering structures. stacking sequences and bending-extension coupling Moreover, efficient analysis methods are required for are compared to numerical results of a detailed Finite pre-dimensioning or optimization processes. Element Analysis. It is shown that a good agreement is Most of the proposed models in literature addressing obtained for all observed configurations. Further, the the analysis of stresses in adhesive joints (Volkersen, effect of the shear deformation of the adherends on 1938, Goland & Reissner, 1944, Hart-Smith, 1981, Ren- the stress distribution in the adhesive is discussed. ton & Vinson, 1975, Tsai et.al., 1998) are joint specif- ic. They focus on only one type of joint design but in References practice adhesive joints may occur in many different Bigwood D.A. & Crocombe A.D. (1989): Elastic analysis joint configurations. A first generalization of these and engineering design formulae for bonded joints models regarding the joint geometry was proposed – In: International Journal of Adhesion and Adhe- by Bigwood and Crocombe (Bigwood & Crocombe, sives 1989, Vol.9, 229-242. 1989). Their model is often referred to as general sand- das Neves P.J.C., da Silva L.F.M., Adams R.D. (2009): wich-type model since it considers only the overlap re- Analysis of Mixed Adhesive Bonded Joints Part I: gion. The model allows for a stress analysis of various Theoretical Formulation – In: Journal of Adhesion joint designs with isotropic adherends, such as single Science and Technology 2009, Vol.23, 1-34. lap joints, L-joints and T-joints. When FRP adherends Goland M. & Reissner E. (1944): The stresses in ce- are used it is important to take shear deformations into mented joints – In: Journal of Applied Mechanics account. This has been done in joint specific approach- 1944, Vol.1, 17-27 es (das Neves et. al., 2009, Tsai et.al., 1998) by employ- Hart-Smith L. (1981): Stress analysis – A continuum ing the First Order Shear Deformation Theory (FSDT). mechanics approach (in adhesive bonded joints) – In this work an efficient general sandwich-type model In: Developments in adhesives 1981, Vol.2, 1-44 for adhesive joints with shear flexible composite adher- Renton W.J. & Vinson J.R. (1975): The efficient design ends including bending-extension coupling (Weißgrae- of adhesive bonded joints – In: The Journal of Adhe- ber et.al., 2014) is presented which allows for the anal- sion 1975, Vol. 7, 175-193 ysis of several joint designs, such as single lap joints, Tsai M., Oplinger D.W., Morton J. (1998): Improved balanced double lap joints, L-joints, reinforcement theoretical solutions for adhesive lap joints – In: patches, T-joints and peel joints. For the case of sym- International Journal of Solids and Structures 1998, metric joints with isotropic adherends a closed-form Vol.35, 1163-1185 analytical solution for the stresses can be obtained. For Volkersen O. (1938): Die Nietkraftverteilung in zug- the general case a system of ordinary differential equa- beanspruchten Nietverbindungen mit konstanten tions with constant coefficients of seventh order has to Lastenquerschnitten – In: Luftfahrtforschung 1938, be solved. The corresponding solution procedure can Vol.15, 41-47 be implemented very efficiently. Weißgraeber P., Stein N., Becker W. (2014): A general In a comprehensive study the solution of the stress dis- sandwich-type model for adhesive joints with com- tributions in the adhesive layer for several joint designs posite adherends – In: International Journal of Ad- with isotropic and laminated adherends with different hesion and Adhesives 2014, Vol. 55, 56-63 Optimization of fatigue behaviour of metallic shear joints Taha Benhaddou1,2, Alain Daidie1, Pierre Stephan1, Clement Chirol2, Jean-Baptiste tuery2 1Institut Clément Ader - Insa de Toulouse, France 2Airbus Operations SAS, Toulouse, France Mechanical fastening is the most widely used tech- by applying torque to the bolt head or to the nut. In nique for assembling aerostructural elements thanks fact, torque specifications can be considered as unre- to several advantages concerning the performance and liable because they can often lead to high uncertain- the cost of the process. However, it presents one major ties in the amount of preload that has actually been drawback, linked to the stress concentration area cre- achieved, and yet preload is the only parameter that ated during hole drilling, which may lead to structural can define the joint behaviour under thermo-mechan- fatigue issues. ical loads. In the case of shear joints, an emerging opportunity to In order to demonstrate the beneficial effect of preload optimize structural joints involves applying the preload on the durability of metallic shear joints, the experi- more accurately. Currently, the clamping force (or mental means used, either for installing or for moni- preload) applied to join the parts together is achieved toring, are preload- oriented ones. This means that 353 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 the scatter on the preload value is reduced from about References 30% (typical torque tightening scatter) to about 10%. Bickford, J. H. (1997). An Introduction to the De- The influence of preload on the fatigue life of metal- sign and Analysis of Bolted Joints, 3rd ed., Marcel lic shear joints is thus demonstrated through the use Dekker. of experimental and numerical methods and a positive Chakherlou, T. N., & Abazadeh, B. (2012). Experimen- correlation is established between the two approaches. tal and numerical investigations about the com- The effect of some preload-related parameters such as bined effect of interference fit and bolt clamping on interfay sealant, radial adjustment and size effect will the fatigue behavior of Al 2024-T3 double shear lap also be covered. joints. Materials & Design, 33, 425–435. Finally, an industrial application case is presented: Boni, L. and Lanciotti, A. (2011), Fatigue behaviour of continuous monitoring of the preload generated by double lap riveted joints assembled with and with- the use of ultrasonic fasteners allows us to perform a out interfay sealant. Fatigue & Fracture of Engineer- global analysis of the joint performance throughout its ing Materials & Structures, 34: 60–71. fatigue life. It also permits fatigue crack initiation to be detected and the effect of preload on its creation to be understood. Microstructure evolution and deformation texture during rolling of TIMETAL407 Gaurav Singh, J. Quinta Da FonsecaCA1, M. Thomas2, M. Preuss1 1The University of Manchester, School of Materials, Manchester, UK 2TIMET UK, Witton, Birmingham, UK TIMETAL407 is a new titanium alloy primarily devel- in the lower temperature band displayes strong basal oped for increased ductility enabling a higher degree pole concentrations inclined about 30 degree towards of energy absorption. In this study, the evolution of mi- rolling direction (RD) together with a weak transverse crostructure and crystallographic texture during rolling texture component. When the material was rolled of TIMETAL407 is examined. For this purpose, TIMET- in the high temperature band, the texture reversed AL407 was first b heat treated before rolling in the showing a strong transverse type of texture and with a upper or lower α + b phase region to 60% reduction relatively weak 30 degree texture component towards in thickness followed by a recrystallisation heat treat- RD. The α texture evolution will be discussed in terms ment. Detailed texture analsysis was carried out using of slip and twinning modes as well as possibilities of b electron back scattered diffraction, while microstruc- rolling texture affecting α texture formation. Further, tural characterization was performed using optical the effect of those two different textures on formabili- and scanning electron microscopy. The material rolled ty of TIMETAL407 are investigated. 354 Talks Topic X 1: General mechanical behavior Talks Topic X 1: General mechanical behavior 355 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Wedge indentation studies of Zr-Cu-based bulk metallic glass V. Nekouie, A. Roy, V.V. Silberschmidt Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Leicestershire, UK Bulk metallic glasses (BMGs) are a relatively new type This technique was employed to apply incremental of materials, which are poised for widespread use in loading on the BMG to study systematically and eluci- the industry thanks to their unique mechanical proper- date the processes of formation and evolution of shear ties. Such mechanical performance is primarily due to bands . Digital image correlation was used to measure the absence of a long-range order in atomic structure local strains during incremental loading of specimens. and a lack of defects such as dislocations, which control A thorough structural characterisation of shear bands ductility in traditional metallic materials. Typically, inor- around the indented region was carried out to under- ganic glasses are brittle at room temperature, showing stand the nature of shear banding. a smooth fracture surface as a result of mode-I brittle fracture. In BMGs, formation and evolution of localised Reference shear bands is a primary deformation mechanism, re- Nekouie, V., Abeygunawardane-arachchige, G., Kühn, sulting in a significant level of plasticity at small scale U., Roy, A. & Silberschmidt, V.V. (2014) Indenta- with a brittle response in the macroscale. tion-induced deformation localisation in Zr-Cu- In this study, a Zr-Cu-based BMG is characterised using based metallic glass, J. Alloys Comp. 615: 93-97. a relatively new technique, namely wedge indentation. Mechanics Behavior of Protein Material Inchul Baek, Myeongsang Lee, Hyun Joon Chang, Jae In Kim, Sungsoo Na Department of Mechanical Engineering, Korea University, Seoul, S. Korea One of the known pathogenesis of several degenerative ent phenotypes based on stacking directions such as and neuro-degenerative diseases, e.g. type II diabetes, parallel and anti-parallel composition, of Human Islet dialysis-related diseases, Creutzfeldt-Jakob disease, Amyloid Polypeptide (hIAPP) by using MD simulations Alzheimer’s disease, Huntington’s disease, Parkinson’s under tensile Steered Molecular Dynamics (SMD) con- disease, etc., is concerned with misfolded, denatured ditions. Here, we investigated the polymorphic charac- proteins called amyloids. The chief reason behind such teristics, which are caused by physiological conditions amyloidosis lies on the amyloid self-assembly process, such as thermal fluctuations. From our results, we have related to the repeated fracture of an immature am- verified the distinct characteristic differences accord- yloid fibril. In order to figure out the disease mecha- ing to the structural array through hydrogen bond frac- nism, establishing the mechanical stability of such am- ture analysis, and elucidated the relationship between yloids therefore takes an essential role, substantiating sequence-structure-property. This study will hopefully the path for treatment. Meanwhile, several research- serve as a template for degenerative disease treatment ers also claim that amyloid proteins can be recognized and also constitute a foundation for the functional bi- as a functional biological materials that can be used in ological materials. nano sensor, bacterial biofilms, coatings, and so on. Due to these reasons, there have been many in vitro Acknowledgements methods to determine the material characteristics via S.N gratefully acknowledges the Basic Science Re- force spectroscopy methods: Atomic Force Microscopy search Program through the National Research Foun- and Optical Tweezers to exemplify. While such meth- dation of Korea (NRF) funded by the Ministry of Sci- ods reveal the quantitative structure stability, mechan- ence, ICT & Future Planning (MSIP) (No. 2007-0056094, ical properties, and functional mechanisms, they yield 2014R1A2A1A11052389). to in silico methods, such as Molecular Dynamics (MD), H.J.C is grateful to the financial support from the Glob- Discrete Molecular Dynamics (DMD) and Elastic Net- al PH.D Fellowship Program through the National Re- work Model (ENM) for example, due to the fact that search Foundation of Korea (NRF) funded by the Minis- they additionally provide a more in-depth informa- try of Education (No. 2014H1A2A1021042) tion in atomic scale about amyloids by visualizing the conformation. In this research, we have unraveled the References structure characteristics and mechanical properties of Pepys MB (2006) Amyloidosis. Annual Review of Med- two different polymorphic structures, i.e. two differ- icine 57: 223-241. 356 Talks Topic X 1: General mechanical behavior Merlini G, Bellotti V (2003) Molecular Mechanisms of Sawaya MR, Sambashivan S, Nelson R, Ivanova MI, Amyloidosis. New England Journal of Medicine 349: Sievers SA, et al. (2007) Atomic structures of amy- 583-596. loid cross-[bgr] spines reveal varied steric zippers. Nature 447: 453-457. Rigidity characterization and fracture analysis of the so- lar-grade multi-crystalline silicon plates at low temperature Lv Zhao, Anne Maynadier, Daniel Nelias Université de Lyon, INSA Lyon, France The rigidity and the fracture behavior of the multi-crys- fracture (intra/intergranulaire manner?) and which talline silicon plates integrated in the solar panels are source initiates the fracture. During 4-point bending of great importance in the fabrication, transportation tests, the tensile side of the specimen is imaged with a and service of the latters. high speed camera. The crack pattern is observed over In our study, we carry out both experimental and nu- the microstructure. The fracture source investigation merical investigations on the multi-crystalline plates relies on the fractography analysis. The micrographies that come from classical ingot growth process (MCSI) are refered to Sherman’s work (Sherman 2009) on the (Chung et al. 2014) and the Ribbon on Sacrificial Tem- single crystals under 3-point bending. plate process (RST) (De Moro et al. 2012). Both types of As regards the experimental obervations, we found plates are laser cut from wafers to obtain 50x50 mm² that the MCSI plates break with multiple cracks-cracks specimens. The RST plates are thinner (around 90µm) are intragranular and straight over one grain. Crack di- than the MCSI plates (170µm). This work aims to char- rection changes at grain boundries. The fracture facies acterize the elastic behavior as well as the fracture analysis indicates that the cracks initiate always form mode and source of these structures. These informa- the edges for both types of plates. Futher microscope tions are of great importance to improve the strength observations reveal some pre-cracks on the specimens’ during production, reduce the waste during handling edges, which are likely due to the laser cutting. and lengthen the lifetime during service. Acknowledgment: The authors would like to thank Elsa Rigidity is characterized by performing 4-point bend- Tupin, Fabrice de Moro and Christian Bellouet from So- ing tests. The Young’s moduli are calculated using the larforce for precious exchange about this work, carried beam deflection theory (Bruneau & Pratt 1962). In or- out in the frame work of DEMOS FUI project. der to verify the experimental assessements, a finite element parametric model is carried out with the com- References mercial FE software Abaqus 6.13. The latter models Chung W.L.; Chuck, H. & Kazuo, N. (2014): Chapiter the grain morphologies using the Voronoi tessellation. 10: Multicrystalline silicon crystal growth for The crystallographic orientations are distributed in an photovoltaic application. Handbook of crystal aleatory manner. The grain boundaries are considered growth: Bulk crystal growth, 2nd edition. as perfect interfaces between the grains. Thus, we as- De Moro F.; Focsa A.; Derbouz K.; Slaoui A.; Auriac signed the same anisotropic elastic behavior given by N.; Lignier H. & Keller, P. (2012) : Multicrystalline sili- [Hall 1967] to all the grains . con solar cells from RST ribbon process. Phys. Status Using the beam theory, the Young’s modulus for the Solidi C 9, 2092-2096. MCSI plates is assessed at 160±8 MPa without distinc- Bruneau, A. & Pratt, P. (1962): The bending deforma- tion in the surface directions. Meanwhile, that for the tion of magnesium oxide. Philosophical Magazine 7, RST plates is estimated at 200±20MPa in the draw- 1871-1885. ing direction and at 210±10MPa in the perpendicular Hall, J.J. (1967): Electronic Effects in the Elastic Con- direction. The FE analysis reveals that the rigidity for stants of n-Type Silicon. Physical Review 161, 756- MCSI plates is reasonable, while that for RST plates is 761. over-estimated. The main contribution to the over-es- Sherman, D. (2009): Fractography of Dynamic crack timation stems from the important variation of the propagation in Silicon Crystal. Key Engineering Ma- thickness for the RST plates. terials 409, 55-64 Regarding the fracture aspect, we investigate how the two types of solar-grade multi-crystalline silicon plates 357 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Quantum field theory approach in mechanics of polycrystal- line materials Vyacheslav Shavshukov, Anatoly Tashkinov Perm National Research Polytechnic University, Russia Most of inorganic structural materials (metallic al- multiple scattering of macroscopic coarse-grained ho- loys, ceramics, minerals etc.) are polycrystalline ag- mogeneous strain upon elastic heterogeneities caused gregates, consisted of macroscopically large quantity by grains disorientation. The solution of the equation of single-crystal grains (crystallites). The mechanical is represented as perturbation series upon these het- behavior of the specimen of polycrystalline material erogeneities. The zero-order solution corresponds is governed by the physical and mechanical process- to absence of scattering and yields well known Voigt es in the grains and interaction of the grains. Thus the approximation. The exact value of strain in any given deformation of polycrystalline material is a cooperative separate grain is defined by multiple scattering on the phenomenon typical for condensed matter physics and heterogeneity of this grain and on all others. The latter mechanics of heterogeneous materials. The passing of terms describe elastic interaction of grains. these processes depend on many parameters, includ- This approach allowed, for instance, to calculate proba- ing stress states of individual grains and its evolution bility density function for stresses in grains under arbi- during macrodeformation. trary macrodeformation of polycrystal [2]. Application Complex structure of polycrystals makes impossible of the method to classical problem of homogenization the exact solution even the simplest elastic problems, gives new formulae for the effective moduli of disor- for instance calculating strains in grains under homo- dered polycrystalline medium [3]. geneous macro deformation. So many approximate The mechanical behavior of polycrystals strongly af- methods were developed. In this paper we present fected by their microstructure. The offered approach new method based on a mathematical analogy be- allows to take into account the influence of grain shape tween the equations of the mechanics of heteroge- and size on stress and strain state of the grain, the elas- neous polycrystalline materials and the equations of tic interaction of adjacent and more remote grains, and quantum theory of particles scattering. This analogy other effects. It is shown that influence of elastic inter- allows to apply the methods of quantum field theory action of grains falls rather fast with distance between to solution of the equations of solid mechanics for het- grains. erogeneous media. The equilibrium equation of boundary value problem Acknowledgements for inhomogeneous strains in polycrystals, written in This work was supported by the Russian Foundation integral form with kernel as Kelvin-Somigliana tensor for Basic Researches grant 13-01-96052. for homogenized medium, is mathematically identical to the Schrödinger equation (written in integral form) References for wave function of particle scattered with many ex- Ziman, J.M. (1972): Principles of the Theory of Solids, ternal potentials. The typical example of the latter 2nd Edition; Cambridge University Press. equation is Korringa-Kohn-Rostocker (KKR) equation Shavshukov, V.E.(2012): Stress field distribution in for wave function of conductance electron in crystal polycrystalline materials. - Physical Mesomechanics. lattice of two-component disordered alloy. The crystal Vol. 15, pp. 85-91. lattice of alloy is regarded as perfect lattice of one com- Tashkinov, A.A. & Shavshukov, V.E. (2013): Field the- ponent disturbed by atoms of another component. The ory approach for describing the deformation of KKR method gives the solution for wave function as multicomponent polycrystalline materials. - Vestnik perturbation series upon this disturbance. SamGTU: phys.-math. No. 4(32), pp. 87-97. Integral equation for strains in polycrystals reads that inhomogeneous strain can be treated as a result of 358 Talks Topic X 1: General mechanical behavior Axial Crash and Crush Response of Novel Nested Tubes ZANA EREN1, FATİH USTA1, ZAFER KAZANCI2 , HALİT S. TÜRKMEN1, ZAHİT MECİTOĞLU1 1İstanbul Technical University, Turkey 2Turkish Air Force Academy, İstanbul, Turkey This paper presents a novel nested design of crash energy. Thus we consider a new geometric crash tube tubes with different cross sections which are subject- model which would be nested with different lengths. ed to axial crashing and crushing. Tubular thin-walled The longest tube would absorb the kinetic energy first, structures with different shapes are widely used in and they could act together with the other tube(s) af- various transportation systems as energy absorbing ter strongest impact effect. This new tube would be components of which dissipation of kinetic energy is lighter than bi tubular crash tubes and alignment of the most important parameter during violent collisions the tubes, geometric parameters would be important. and crashes. In this study, explicit nonlinear analysis of the tubes The effect of the nested design shows that when a tube which are made from Dual-Phase steel 600 and Alu- fails under progressive buckling, the initial peak force minum 6063 are done in ABAQUS and Ls-DYNA pro- is much greater than the subsequent peak. In many in- grams. The virtual crush and crash test data are used stances, these tubes are used to absorb energy in cars to aid the entire development of a new design. The and the high force peaks lead to high acceleration on objective is to show that, nested tube design provides the vehicle occupants during an accident/impact event. decreasing peak forces gradually while increasing ab- An ideal energy-absorbing device should therefore sorbed energy. Also, the mesh efficiency is measured cause a uniform deceleration during the entire stroke. by changing element lengths in both ABAQUS and This ideal structure would absorb the shock first and Ls-DYNA. then deform under progressive buckling to absorb the Neutron diffraction and imaging for industrial and engineer- ing applications Anna Paradowska 1Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia The OPAL research reactor at ANSTO has a number of improved product reliability, enhanced design perfor- neutron instruments available for science and engi- mance, reduced production cost, and extended life neering applications. The instruments have a unique prediction on significant engineering assets (e.g. pow- non-destructive ability to determine critical aspects of er-station utilities, gas pipelines, aircrafts, trains, etc.). a wide variety of material systems. This includes surfac- This presentation will focus on two instruments in par- es, defects, fine scale dispersions, texture and residual ticular: Kowari, the strain scanner and crystallographic stresses. This information can provide a direct impact texture measurement system and Dingo the radiogra- into optimization of modern manufacturing processes, phy/tomography instrument. 359 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Talks Topic X 2: General mechanical behavior 360 Talks Topic X 2: General mechanical behavior Preparation and Characterization of Neat and Thermally- treated Silicon Carbide Fibers-reinforced Gypsum Cements Y. E. Greish1, H. F. El Maghraby2, O. Gedeon3, O. Alnuaimi, M. S. Katsiotis, K. Polychronopoulou4 1Department of Chemistry, College of Science, UAE University, UAE 2Department of Ceramics, National Research Centre, Egypt 3Department of Glass and Ceramics , Institute of Chemical Technology, Czech Republic 4Department of Mechanical Engineering, Khalifa University of Science and Technology, UAE Synthetic biomaterials that are intended to partially ternal morphology of the cement composites was eval- or totally replace defective hard tissues are strong- uated using SEM-EDX technique. Cement composites ly recommended to have matching composition and containing neat and thermally treated SiC fibers were properties to those of natural hard tissues. Two main also subjected to Tensile strength measurement as a components make up the construction of hard tissues; function of the concentration of SiC. Cement compos- namely hydroxyapatite (HAp), and collagen. In nature, ites were further soaked in protein-free SBF media for HAp nanocrystals deposite along and onto the surfaces up to 14 days to evaluate their preliminary bioactivity. of nanofibrous collagen fibers, making a mechanically SBF-treated samples were investigated by SEM-EDX, interlocked assembly that provides hard tissues with while aliquotes were analyzed every 2 days for chang- their unique mechanical properties (Buckwalter 1996). es in the concentrations of Ca2+, SO 2- 4-4 , and SiO4 ions Upon formation of defects, bone cavities are usually with time. treated with cements. However, a major drawback of Results showed no chemical interaction between the most currently exisiting cements is their low mechan- components of the cement during their solidification. ical stability and to some extent their limited bioac- A homogeneous distribution of the SiC fibers within tivity. In the current research, a calcium sulfate-based the gypum set cement was reflected on stable me- bone cement has been studied after incorporating chanical performance of the composites, with an over- neat and thermally treated SiC fibers. Calcium sulfate all improvement in the tensile strength by addition of cement is one of the early known bone cements and 10% SiC fibers. Moreover, SEM observations showed is a known bioresorbable material. On the other hand, growth of HAp-like spherolites onto the SiC fibers, es- SiC is a structural ceramic material that has been also pecially those thermally pre-treated. The advantages recognized as a bioinert material (Zhang 2009). Upon of the currently studied composites are, therefore, the thermal treatment in air, partial oxidation of the SiC enhancement of the bioactivity, the ability to control fiber’s surface takes place leading to the formation of a the biodegradation of the composite by controlling the silica (SiO2) layer. Materials containing SiO2 have poten- proportion of POP in the original powder mixture of tial bioactivity where hydration of SiO2 yields hydrated the reactants, as well as the slight improvement in the silica layer which has been long shown to nucleate HAp mechanical properties by the addition of 10 wt% SiC after implantation or when soaked in simulated body fibers. fluid (Li 1992). Therefore, the rational of incorporating SiC fibers is to work on improving the mechanical per- References formance of the cement and introduce bioactivity by Buckwalter JA, Glimcher MJ, Cooper RR, Recker R. virtue of the SiC oxidized fibers. Instr Course Lect. 1996;45:371-86. In the current study, the formation of a novel cement Zhang Lei-Lei, Li He-Jun, Li Ke-Zhi, Lu Jin-Hua, Shen of gypsum reinforced with up to 25 wt% SiC fibers has Xue-Tao, Lan Feng-Tao. Surf. Rev. Lett. 2009; 16, 683 been investigated. Setting times of the prepared com- Li P, Ohtsuki C, Kokubo T, Nakanishi K, Soga N, Naka- posites were recorded until complete solidification, mura T, Yamamuro T. J Amer Ceram Soc. 1992; 75: phase composition of the composites was studied us- 2094–2097 ing XRD, FTIR, DTA and TGA techniques. In addition, in- 361 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Phase-field modeling for microstrucurure formation of metal foam materials Takuya Uehara Yamagata University, Yonezawa, Japan Metal foam materials have been developed and uti- vious models (Uehara & Suzuki 2012, Uehara 2012). In lized in a wide variety of fields owing to their remark- this paper, the model is extended to three-dimensional able advantages. Characteristics of these materials foam structure. depend strongly on the microstructure as well as the First, Kelvin-cell structure is constructed and the sta- properties of base metal, and hence the control of the bility is verified by providing various degrees of fluc- microstructure, i.e. shape, size and their distribution of tuation in regularity. A rhombic dodecahedron, which the foam cells, is of great importance. Computer sim- is one of the close-packed space-filling structures, is ulation is indispensable for this purpose, since direct also tested, and the advantageous stability of Kelvin observation of the dynamic process of foam formation cell was confirmed. Then, random seeding conditions is difficult. However, the mechanism of the foam struc- are introduced assuming realistic process. As a result, ture formation has not been clarified yet, thus a nu- distorted cells are formed in the early stage, but they merical modeling is necessary. revealed to promptly change the morphology to be Phase field model is a promising tool; various micro- stable convex polyhedra. The mechanical properties of structures, such as dendrite, lamellar, cellular, and the metal foam consisting of the simulated structures polycrystalline structures, are sucessfully regenerated. will be numerically evaluated in the next stage of our Most phase field models describe liquid and solid phas- study. es to account for the solidification and in-solid phase transformation. In this paper, the conventional model References is modified to simulate foam structure formation. Sye, R. I. & Sethian, J. A. (2013): Multiscale modeling Foam structure considered in this paper is closed-cell of membrane rearrangement, drainage, and rupture type, in which small vacancies or cells surrounded by in evolving foams, Science 340, 720-724. thin solid walls are distributed. This structure is similar- Weaire, D & Phelan, R. (1994): A counter-example to ly found in bubble foam made by soap or froth. These Kelvin’s conjecture on minimal surfaces, Phil. Mag. kind of structures have long been studied, and even Lett. 69, 107-110. recently investigations are actively in progress (e.g. Sye Uehara T. & Suzuki H. (2012): Numerical simulation of & Sethian 2013). Kelvin cell is one of the most sophisti- homogeneous polycrystalline grain formation using cated structures, which had been considered to be the multi-phase-field model, Appl. Mech. Mater. 197, best structure making the total surface area of the cell 2610-2614. boundaries smallest in any space-filling structures until Uehara T. (2012): Grain-size equalization model using alternative structure was found by Weaire and Phelan multi-phase-field model, Proc. 7th Int. Workshop on (Weaire & Phelan 1994). Uehara made an approach to Modeling Crystal Growth, 82-83. this problem using a two-dimensional phase-field sim- Uehara T. (2014): Numerical simulation of foam struc- ulation, and proposed an additional term which con- ture formation and destruction process using phase- trol the cell volume (Uehara 2014) based on their pre- field model, Adv. Mater. Res. 1042, 65-69. Fiber-reinforced Calcium Sulfate Bone Cement Composites with Enhanced Bioactivity, Mechanical Properties and Con- trolled Biodegradability Yaser E. Greish1, Abdel hamid I. Mourad2, Nuha F. Attia1 1Department of Chemistry, College of Science 2Department of Mechanical Engineering, College of Engineering United Arab Emirates University, Al Ain, UAE Hard tissues are natural composites of inorganic nanofibers and the HAp nanocrystals growing on them (hydroxyapatite-HAP), and organic (collagen) provides the well known unique mechanical stability components. The interlocking between the collagen of hard tissues (Buckwalter 1996). In case of partial 362 Talks Topic X 2: General mechanical behavior fractures; bone or dental cements are often used. composites were studied. Phase composition and A widely used polymer; polymethyl-methacrylate morphology were investigated by XRD, FT-IR, TGA, (PMMA), has been long applied in this regard and SEM techniques. Both tensile and compressive (Rohmiller 2002). However, this polymer is classified as strengths of the composites were measured. a bioinert material that can be accepted by the human Preliminary in vitro performance tests were carried out body without having a positive interaction; bioactivity, in simulated body fluids and were followed by studying with the surrounding tissues. Therefore, attempts have the variations of concentrations of certain ions in been done to introduce more bioactive bone/dental the solutions and morphology of the SBF-treated cements to replace PMMA. composites after soaking for up to 14 days in these Gypsum has been always considered a bioresorbable solutions. material and has wide scope of biomedical applications. Results showed an overall enhancement in the In fact, gypsum is one of the first known biomaterials bioactivity of the composites as a result of the addition to be introduced to augment broken hard tissues of wollastonites; both as-received and acid-treated. (Orsini 2004). However, gypsum as a calcium sulfate is A slight decrease in the mechanical properties of characterized by its fast resorption after implantation, the composites was observed with the addition which may lead to limited stability of the cement after of wollastonite fibers. Phase composition of the use. In addition, its chemical composition is different composites indicated no interference of wollastonite from that of the mineral components in hard tissues; with the formation of gypsum. The advantages of HAp. Due to these concerns, a bioactive calcium the currently studied composites are, therefore, silicate; known as wollastonite, has been considered the enhancement of the bioactivity and the ability to be added to gypsum to improve its bioactivity. to control the biodegradation of the composite by Wollastonite is relatively more stable than gypsum in controlling the proportion of POP in the original the body and is known to bond to the surrounding powder mixture of the reactants. bone tissue through the formation of bone apatite-like layers on its surfaces after implantation (Liu 2008). References The current study investigates the formation of a Buckwalter JA, Glimcher MJ, Cooper RR, Recker R. composite of gypsum and wollastonite at weight Instr Course Lect. 1996;45:371-86. percentages of 1, 5, and 10%. Three types of Orsini G, Ricci J, Scarano A, Pecora G, Petrone G, Lezzi wollastonites; varying in their degree of crystallinity G, J. Biomed. Mater. Res. Part B: Appl. Biomater. were used in the study. Powder mixtures of a gypsum 199–208 , 68B (2004). precursor; Plaster of Paris (POP) and wollastonite Michael T. Rohmiller, MD*, Dugan Schwalm, MS, R. were well blended prior to reactions with water. The Chris Glattes, MD, Tarek G. Elalayli, MD, Dan M. effect of using as-received wollastonite fibers or those Spengler, MD. The Spine Journal, 255–2602, 2 treated in acidic media on the setting reactions, phase (2002) composition, morphology, mechanical properties and Xuanyong Liu , Macro Morra , Angelo Carpi , Baoe Li. the preliminary in vitro performance of the produced 526-529 , 62 (2008) Mixed Elastic Variational Formulation of Composite Plates Based on Dimension Reduction Method Mohammad Javad Khoshgoftar1, Mohammad Mirzaali2 1 Department of Mechanical Engineering, Faculty of Engineering, Arak University, Iran, 2 Institute for Surgical Technology and Biomechanics, University of Bern, Switzerland In the present research, a new modeling approach for the Hellinger-Reissner principle. Moreover, a compar- elastic composite plates is studied. By adopting mixed ison between current work and other theories such variational formulation and dimension reduction as Classical and First Order Shear Deformation Theory method along the thickness, a general plate model is has been done, and advantages of this method are dis- derived. Firstly, shape functions weighted with arbi- cussed Needless of shear correction factor, more accu- trary coefficients adopted along the thickness of plate rate results and independent stress from displacement for both displacement and stress field and then, partial filed are some advantages of this approach. differential equation system of plate is derived by using 363 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Effect of Friction on Material Mechanical Behaviour in Non- equal Channel Multi Angular Extrusion (NECMAE) Mohamed S. El-Asfoury1, Mohamed N. A. Nasr 1,2, Ahmed Abdel-Moneim1 1 Dept. of Materials Science & Engineering, Egypt-Japan University of Science & Technology, Alexandria, Egypt 2 Dept. of Mechanical Engineering, Faculty of Engineering, Alexandria University, Egypt Severe plastic deformation (SPD) is typically used to The current work represents the second step in devel- achieve significant grain refinement, which in turn oping the NECMAE process, where the effect of friction results in higher mechanical strength and crack resist- on process mechanics is examined. FEM was used to ance, but lower ductility. For bulk ultra-fine grain (UFG) model a NECMAE process with 50% area reduction, materials, additional requirements - such as, homo- where different values were assigned to the friction geneity and reasonably equi-axed grains with the ma- coefficient (0, 0.1 and 0.2). A two-dimensional ther- jority of grain boundaries having high angles of disori- mo-mechanical plane strain model was built using the entation - are required. Different SPD techniques are commercial software ABAQUS/Explicit. The workpiece currently available, where the equal channel angular material is pure aluminium. The model was validated pressing (ECAP) and high pressure torsion (HPT) are the by comparing the predicted average strain values to most widely used for producing UFG materials. available data in the literature. The ECAP technique was first introduced by (Segal et The coefficient of friction was found to affect the cor- al., 1981). However, in order to achieve higher degrees ner gap size, as friction tends to increase the sticking of refinement and better degrees of homogeneity, dif- possibility of the workpiece to the die. Accordingly, this ferent modifications have been presented; for exam- helps in filling up the dead zone, and results in higher ple, equal channel multi-angular pressing (ECMAP), temperatures especially near the die surface. However, and non-equal channel angular pressing (NECAP), as expected, the central portion of the workpiece was which impose higher strains compared to ECAP (Hasani found to be slightly affected. Finally, cases with higher et al., 2010). Another example is the twist channel coefficient of friction were found to have higher and angular pressing (TCAP), where a twist angle is intro- much uniform plastic deformation, as well as higher duced at the die inlet in order to increase the imposed required punching loads. strains and improve homogeneity (Kocich et al., 2013). Even though these modified processes showed better References results than ECAP, they are still characterized by irregu- Segal, V. M., V. I. Reznikov, A. E. Drobyshevskii, and lar shear strain distribution, where the deformation in- V. I. Kopylov. 1981. “Plastic Metal Working by Sim- homogeneity index increases with corner angle, strain ple Shear.” Izvestia Akademii nauk SSSR. Metally hardening and friction effects. 115–23. In an effort to improve the degree of homogeneity and Hasani, Arman, László S. Tóth, and Benoıt̂ Beausir. impose higher strains, the current authors have de- 2010. “Principles of Nonequal Channel Angular veloped a new process, with the aid of finite element Pressing.” Journal of Engineering Materials and modelling (FEM), which combines ECMAP with extru- Technology 132(3):031001. Retrieved November 10, sion (El-Asfoury et al., under review). The new process, 2014 named “non-equal channel multi angular extrusion Kocich, Radim, Lenka Kunčická, Milan Mihola, and (NECMAE)”, uses a die with three channels. The first Kateřina Skotnicová. 2013. “Numerical and Experi- two represent a standard ECAP process, while the third mental Analysis of Twist Channel Angular Pressing one experiences a reduction in cross-sectional area. (TCAP) as a SPD Process.” Materials Science and Different percentages of area reduction (10%, 30% and Engineering A 563:86–94. 50%) were examined at well-lubricated conditions. It El-Asfoury M., Nasr M. and Abd Elmoneim A. “Model- has been shown that, NECMAE improves the degree of ling Material Behaviour during Non-equal Channel uniformity and imposes higher magnitudes of strains; Multi Angular Extrusion (NECMAE) - A New Pro- i.e., more grain refinement. Such results were attribut- cess”, under review. ed to back pressure effects, as well as the change in the shear angle during deformation. 364 Poster Topic A: Multiscale phenomena in plasticity Poster 365 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Poster Topic A: Multiscale phenomena in plasticity 366 Poster Topic A: Multiscale phenomena in plasticity The effect of hydrogen on the macroscopic strain localization of steels Svetlana Barannikova1,2, Anatoly Malinovsky2, Dmitrii Pestsov2 1Institute of Strength Physics & Material Science, SB RAS, Tomsk, Russia 2Tomsk State University of Architecture & Building, Tomsk, Russia Embrittlement due to hydrogen (H) involves a vast loss plastic distortion tensor components; the kinetics of of mechanical properties with the following character- nuclei motion can be determined from the temporal istics such as, for example, decrease of ductility and evolution of nuclei. fracture tension with the increase of H concentration The samples were electrolytically saturated with hy- (Sofronis, Liang & Aravas 2001). This phenomenon pos- drogen in a thermostatted three-electrode electro- es a serious practical problem, the solution of which chemical cell with graphite anode, operating at a determines the durability and safety of operation of a controlled constant cathode potential of U = –600 mV steel structure. Previously, we presented experimental (relative to silver chloride reference electrode) in a 1 N data (Zuev & Barannikova 2010) according to which sulfuric acid solution containing 20 mg/l thiourea. The plastic strain development in solids exhibited a local- hydrogenation was effected at 323 K for 24 h after pre- ized character over the entire process. This phenome- liminary purging the solution with nitrogen. The cur- non is especially clearly manifested on a macroscopic rent–voltage curves were recorded using an IPC-Com- scale, where the patterns of strain localization are re- pact potentiostat. lated to the deformation hardening operative on the It has been found that the propagation velocity and corresponding stages of straining. The main aim of this wavelength of the localized plasticity waves are af- investigation was to elucidate the effect of dissolved fected by the strength characteristics of steels, which hydrogen on the macroscopic plastic flow localization are determined by the interstitial impurity content H. patterns in tensile strained steels. Therefore, the wave patterns of macroscopic localized The investigations were performed for FCC monocrys- plasticity appear to be useful for a detailed analysis of tals of the austenitic stainless steel (Fe-18%Cr-12%Ni) plasticity exhibited by real metals and alloys. The use and BCC polycrystals of low-carbon steel (Fe-0.07%C). of such patterns can help derive more exhaustive and The samples had a working part with dimensions of accurate information about the processing limits of a 25·5·1 mm and were tensile strained at 300 K on an material relative to conventional characteristics, e.g. Instron testing machine at a mobile clamp velocity of elongation and reduction of cross-section. 8.3·10-6 m/s. The stress-strain diagram was obtained simultaneously with measuring the fields of the dis- References placement vectors r(x, y) with the aid of double-ex- Sofronis, P., Liang, Y. & Aravas, N. (2001): Hydrogen posure speckle photography technique. A special de- induced shear localization of plastic flow in metals vice was also designed (Zuev, Gorbatenko & Pavlichev and alloys: European Journal of Mechanics – A: 2010); it had field of vision ~100 mm; spatial resolu- Solids. Vol. 20: 857-872. tion comparable to optical microscopy ~1…2 μm and Zuev, L.B. & Barannikova, S.A. (2010): Evidence for the real-time mode of operation. This enabled reconstruc- existence of localized plastic flow auto-waves gen- tion of displacement vector fields r(x, y) for the sam- erated in deforming metals: Natural Science, Vol. 2: ple surface. On the base of this data, the plastic dis- 476-483. tortion tensor is evaluated for the deforming sample Zuev, L.B., Gorbatenko, V.V. & Pavlichev, K.V. (2010): in the coordinates x, y and z, i.e. longitudinal ( ex ), Elaboration of speckle photography techniques for transverse ( e y ), shear ( exy = e yx ) and rotation ( ωz plastic flow analyses: Measurement Science and ) components. This technique can visualize localized Technology, Vol. 21, 054014: 1-5. plastic flow nuclei, using the spatial distributions of 367 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Atomistic analyses of nucleation and propagation behavior of ridge shaped kink band in long-period-stacking-ordered phase Ryosuke Matsumoto, Masayuki Uranagase Kyoto University, Kyoto, Japan Materials with strong plastic-anisotropy typically show (1) From the bending deformation of beams, it is kinking deformation under a compressive deformation. confirmed that, initially, (a) non-basal slips occur, and Deformation boundaries of kinking deformation (kink (b) low angle boundaries are formed through cross- boundary) do not have specific misorientation-angle, slip mechanism described in Matsumoto 2013. When and thus it is considered that kinking deformation the misorientation angle reaches about 20°, (c) the occurs by unclear mechanisms different from twinning boundaries become dislocation source, and (d) the deformation. dislocation emission from the boundaries drastically Recently developed Mg alloys that contain long peri- increases the misorientation angle of themselves. od-stacking-ordered (LPSO) phases have attracted con- (2) The compressive deformation of square columns siderable attention because they have been reported with initial TB indicated that once tilt boundary is to exhibit excellent mechanical properties, including formed in the LPSO phase through some processes, high yield stress and reasonable ductility (Kawamura such boundary emits a lot of dislocations to both sides 2001). The LPSO phases deform by generating a of the boundary under compressive load and forms lot of ridge-shaped deformation bands (Hagihara ridge shaped kink band. 2010). Based on the detailed observation of the kink boundaries, the deformation bands are confirmed References special type of kink band. It is also examined that these Hagihara, K. & Yokotani, N. & Umakoshi, Y. (2010): deformation bands appear with shorter timescale than Intermetallics, 18: 267-276. tens µs (Hagihara 2013). This study aims to reveal the Hagihara, K. & Fukusumi, Y. & Yamasaki, M. & formation mechanisms of ridge shaped kink band in Matsumoto, R. & Honnami, M. & Izuno, H. & LPSO phases. Nakano, T. & Kawamura, Y. (2013): Deformation In this study, we performed molecular dynamics behavior of LPSO phase and Zn accompanied by simulations. The model material employed is LPSO kink band formation, 8th Pacific Rim International phase with 10H stacking which is composed by single Congress on Advanced Materials and Processing element whose interatomic interaction is described by 2013; 2: 973-978, Waikoloa. the Lennard-Jones potential (Matsumoto 2013). Here, Kawamura, Y. & Hayashi, K. & Inoue, A. (2001): we performed two kinds of MD simulations; (1) bending Materials Transaction, 42: 267-276. deformation of beams under compressive load parallel Matsumoto, R. & Uranagase, M. & Miyazaki, N. to the basal plane, and (2) compressive deformation (2013): Materials Transaction, 54: 686-692. of square columns including initial dislocations which constitute TB (tilt boundary). Most simulation models are composed by about 1.5 million atoms, and all simulations were performed at 300 K. Microtension behavior of hydrogen-containing metastable austenitic stainless steel Ryo Matsuoka, Kaoru Koga, Yoji Mine, Kazuki Takashima Kumamoto University, Kumamoto, Japan in ductility due to deformation localization in the pres- The susceptibility to hydrogen embrittlement of aus- ence of hydrogen. This difference is related to the intrin- tenitic stainless steels is dependent on their austenite sic tendency to the deformation-induced martensitic stability. The metastable austenitic stainless steel such transformation. On the other hand, fractographic obser- as type 304 suffers from severe HE, whereas the type vation often showed a planar fracture feature in HE aus- 310S stable austenitic steel exhibits a little degradation tenitic stainless steels, and it was presumably formed in 368 Poster Topic A: Multiscale phenomena in plasticity association with annealing twin boundaries (Fukuyama, In the uncharged single-crystalline specimen, after 1985). However, the role of twin boundary in the HE of yielding occurred at a stress of 270 MPa, the 910 MPa metastable austenitic steels has not yet been clarified. ultimate tensile strength and the 70% strain-to-failure The present study applied microtension testing to the were attained through a significant strain hardening. analysis of the HE in bicrystals, with particular focus on The uncharged bicrystalline specimen exhibited a the effect of twin boundary on the deformation-induced higher yield stress, but lower ultimate tensile strength martensite transformation. and strain-to-failure. This is because the deformation The material used in the present study was a solution was hindered by the twin boundary and was localized at treated 304 stainless steel with an average grain size of 60 the one grain. In both the single- and bicrystalline spec- μm. Microtension specimens with 20μm×20μm×50μm imens, the yield stress was increased but the ductility dimensions of the gauge section were fabricated using was drastically decreased by the hydrogen pre-charge. focused ion beam. Single-crystalline specimens and As for the fracture morphology, the hydrogen-charged bicrystalline specimens with a twin boundary were single- and bicrystalline specimens exhibited a quasi- prepared so that the loading direction (LD) is parallel to cleavage and a planar facet fracture, respectively. The [111]. For the bicrystalline specimen, the twin boundary OIM observation of the deformation microstructures is arranged parpendicular to the LD. Hydrogen was ca- suggests that hydrogen-induced fractures occurred thodically charged at a current density of 27 A m-2 in a along the martensite block and austenite twin pH = 3.5 aqueous solution of H2SO4. Specimens were boundaries. hydrogen-charged for 7h at a temperature of 353K. Mi- Reference crotension testing was performed at room temperature Fukuyama, S., Yokogawa, K., Kudo, K., & Araki, M. in the atmospheric air and at a loading rate of 0.1 μm s-1. (1985): Fatigue Properties of Type 304 Stainless After tensile test, the deformation microstructure was Steel in High Pressure Hydrogen at Room observed by orientation imaging microscopy (OIM). Temperature, Trans. Jpn. Inst. Met, 26: 325-331. Microtension behaviour of dual-phase steel subjected to pre-straining Shinya Ogata1, Yoji Mine1, Kazuki Takashima1, Hiroshi Shuto2, Tatsuo Yokoi2 1Kumamoto University, Kumamoto, Japan 2Nippon Steel & Sumitomo Metal Corporation, Oita, Japan fraction of 29 vol.% was obtained by heating at a tem- The dual-phase (DP) steel is a high tensile strength perature in (α+γ) two-phase region followed by wa- steel consisting of a soft ferrite phase and a hard mar- ter cooling. Pre-strains were introduced by cold rolling tensite phase. This steel is widely used for automotive (CR) at reductions of 60% and 88% in thickness. The applications because of its enhanced balance between deformation microstructure was characterized using strength and ductility. However, its low hole expand- electron backscatter diffraction analysis. Microten- ability is often a major drawback. When the DP steel sion specimens with 20μm×20μm×50μm dimensions is subjected to deformation, strain partitioning occurs of the gauge section, including the ferrite/martensite between the ferrite and marternsite phases, resulting in the inhomogeneity of the strain distribution (Park, interface, were fabricated using focused ion beam. 2014). The local strain, which depends on the con- Microtension testing was performed at room temper- straint conditions, differs from the macroscopic strain. ature in the atmosphere and at a loading rate of 0.1 Thus, it is important to comprehend the mechanical μm min-1. characteristics of the microstructures evolved by local- Ferrite grains with continuously gradated crystallo- ized deformation through the stress concentration at graphic orientations were observed after 60% CR. By the interface between the ferrite and martensite phas- 88% CR, an ultrafine-grained ferrite microstructure was es. In the present study, we conducted microtension also evolved in the region neighbouring the martens- testing on inhomogeneous microstructures evolved by ite phase. The grain refinement presumably occurred pre-straining with cold rolling, with particular focus on by severe deformation at the interface between the the role of the fine-grained ferrite microstructure in ferrite and martensite phases. In the 60% CR spec- the deformation and fracture process of the DP steel. imen exhibiting an yield stress of ~720 MPa and an The material used in the present study was a low car- elongation-to-failure of ~10%, yielding occurred in the bon steel, composed of 0.14 C, 1.00 Mn (mass%), and coarse ferrite grain, leading to a chisel-edge failure. By the balance Fe. A DP microstructure with a martensite contrast, the 88% CR specimen exhibited high yield 369 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 strength but low ductility when compared to the 60% Reference CR specimen. In the 88% CR specimen, a shear type Park, K., Nishiyama, M., Nakada, N., Tsuchiyama, T. fracture occurred in the ultrafine-grained ferrite with- & Takaki, S. (2014): Effect of the martensite distri- out necking. This may be attributed to the strain local- bution on the strain hardening and ductile fracture ization at the ultrafine ferrite grains. In this presenta- behaviors in dual-phase steel, Mater. Sci. Eng. A, tion, we will discuss the plastic deformation transfer at 604: 135–141. the ferrite/martensite interface. Adaptive boost molecular dynamics method for study of rare events in plastic deformation Naomchi Tsuji1, Akio Ishii1, Junping Du1, Shigenobu Ogata1, 2 1Osaka University, Japan 2Kyoto University, Japan Molecular dynamics (MD) is a powerful technique to In this study, we applied the ABMD method to the she- study the plastic deformation of materials under atom- ar-coupled grain boundary migration and the dislocati- ic scale. However, because of the limited time-scale on nucleation from a corner of nanopillar and a grain (nanoseconds) in regular MD simulation, the strain boundary in Cu. First, the behavior of a symmetric tilt rate in MD (106 1010~ s -1) is orders of magnitude higher grain boundary in Cu crystal is simulated under shear than that in experiment (10-6~10 1 s-1). So it is difficult stress along the grain boundary. The grain boundary to analyze long time-scale phenomena by combining migration velocity and strain rate consistent with those MD simulations and experiments, such as shear-cou- in experiments are obtained. The results demonstra- pled grain boundary motion and dislocation nucleation te a mechanism transition from displacive to diffusive from surface or grain boundary. motions with increasing temperature. Next, we applied An accelerated MD simulation method, adaptive boost this method to dislocation nucleation from a corner of (AB) MD method [1], have been developed to study nanopillar and a grain boundary of Cu. In the simulati- the rare events in material science. In this method, the on, a half partial dislocation loop is emitted from the smooth histogram of collective variables (CVs) is firstly corner of nanopillar and grain boundary, and propaga- evaluated by regular MD simulation. CVs can be used tes on the boosted {111} planes. The dislocation nucle- to characterize the accelerated phenomena and have ation rates, which is beyond the ability of regular MD, one or more degrees of freedom. Then, a boost po- are obtained under a wide range of temperature and tential is determined by , and is added to the original strain. The activation parameters, such as activation free energy surface. A fictitious force on particle can enthalpy and activation volume, are evaluated from be evaluated based on boost potential, . Such adaptive the simulations. and cumulative operations are repeated until state transition occurs. The time acceleration is evaluated by References the hyperdynamics theorem [2], the relationship be- [1] Ishii, A., Ogata, S., Kimizuka, H. & Li, J. (2012): tween the transition period and the actual transition Adaptive boost moelcular dyanmics simulation of period can be expressed as . carbon diffusion in iron, Physical Review B, 85-6, The definition of CVs is correlated to the atomic pro- 064303. cess in the rare events. We define CVs as , where is [2] Arthur, F. Voter (1997): Hyperdynamics: Accelerat- total number of atoms, is prepared parameter, and is ed Molecular Dynamics of Infrequent Events, Physi- coordinate of atoms. By this definition, it is possible to cal Review B, 78-20, 3908. accelerate rare events that can be characterized by lin- ear combination of coordinate of atoms. 370 Poster Topic A: Multiscale phenomena in plasticity Quantitative evaluation of dislocation nucleation as thermal activation process via atomistic simulations Masayuki Uranagase, Ryosuke Matsumoto Kyoto University, Kyoto, Japan Dislocation nucleation, which is one of the elementa- ation (Uranagase 2014) and evaluate the activation ry processes of deformation, plays an important role free energy of nucleation of basal and prismatic dis- for deformation when there are less pre-existing dis- locations. locations, e.g., compression of micro pillar metals. Using the method mentioned above, we studied the However, deformation due to dislocation nucleation is dependence of the activation free energy of disloca- not confined to the case where the size of the speci- tion nucleation on ambient temperature and applied men is extremely reduced. For instance, it is proposed stresses in detail. For instance, it is possible to estimate that formation of a kink band occurred in recently the shear stress in slip direction necessary for disloca- developed magnesium (Mg) alloy (Kawamura 2001) tion nucleation in realistic time scale if the activation based on dislocation nucleation (Hagihara 2010). This free energy obtained from atomistic simulations is kink band is contributed to overwhelming strength fitted to analytic expression. We also discuss the lin- of this alloy with keeping fair ductility, which extends ear relation between the enthalpic and the entropic possibility for application of Mg to various industrial contributions to the activation free energy, which are applications. Therefore, it is worth quantitatively eval- obtained from temperature dependence of the activa- uating dislocation nucleation for understanding some tion free energy, and the influence of normal stress on kinds of macroscopic deformation modes. degree of nucleation of dislocation. In this study, we consider dislocation nucleation in pure Mg via atomistic simulations. Atomistic simula- References tion enables to analyze detailed mechanisms of defor- Hagihara, K. et al. (2010): Plastic deformation behav- mation, though applicable scales of time and space are ior of Mg12YZn with 18R long-period stacking or- strictly restricted because of its heavy computational dered structure. – Intermetallics, 18: 267-276. cost. In particular, when one treat elementary process Kawamura, Y. et al. (2001): Rapidly Solidified Powder of deformation, one has to overcome the problem Metallurgy Mg97Zn1Y2 Alloys with Excellent Tensile comes from restriction of time scale. Here, we adopt Yield Strength above 600 MPa. – Mater. Trans., 42: metadynamics method (Laio 2008) to solve this prob- 1172-1176. lem. In metadynamics method, collective variables, Laio, A. and Gervasio, F. L. (2008): Metadynamics: a which characterize the phenomenon focused on, are method to simulated rare events and reconstruct initially set. Then, history dependent bias potential is the free energy in biophysics, chemistry and materi- added to the system to urge the change of collective al science. – Rep. Prog. Phys., 71: 126601. variables. This bias potential is also used for construc- Uranagase, M. and Matsumoto, R. (2014): Thermal tion of free energy surface in the space spanned by col- activation analysis of enthalpic and entropic contri- lective variables. In our work, we construct one dimen- butions to the activation free energy of basal and sional collective variable for dislocation nucle prismatic slips in Mg. – Phys. Rev. B, 89: 224103. 371 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Poster Topic B: Mechanical behavior 372 Poster Topic B: Mechanical Behaviour Residual stress evaluation of shot peened Ag-based contact materials via diffraction technique Seung-Yub Lee1, Jingjing Ling1, Hyo-Soo Lee2, Min-Ha Lee2 1 Department of Applied Physics and Applied Mathematics, Columbia University, New York, USA 2 Korea Institute of Industrial Technology, Incheon, Republic of Korea Silver cadmium oxide (Ag-CdO) is one of the most pop- SEM measurement were carried out for the hardness ular electrical contact materials due to its high elec- test and phase analysis. trical conductivity from Ag, and excellent wear & arc Since surface residual stress is also a critical prameter resistance from CdO. For example, the 90% Ag and 10% affecting mechanical stability, Columbia University in- CdO has been widely used in medium to heavy duty vestigated residual stress under biaxial stress assump- switches and controls, wall switches, motor starters, tion with the traditional sin2ψ technique (Noyan, 1987). DC switches and relays, AC and DC circuit breakers, mo- Experiments were performed at the synchrotron beam tor protectors, etc, because it has a high current carry- line, X20A, in the National Synchrotron Light Source ing capability, low arc erosion, high conductivity (80% (NSLS) in Brookhaven National Laboratory. IACS), good hardness (75 in HR-15T), and great sticking Residual stress evaluation from the silver phase shows resistance (Brainin Company, 2015). that shot peening was not much effective in terms of However, due to the imminant environmental regula- stress reinforcement, especially when followed by the tions, there have been a lot of efforts to replace the thermal oxidation process to form ZnO or CdO. How- toxic cadmium with other alternatives without com- ever, it affected internal oxidataion behavior different- promising surface durability and electrical conduc- ly for each alloy system. This seems to be related to tivity; the most successful CdO substitution so far is the stress-induced diffusion mechanism as well as in- the silver tin oxides (Ag-SnO2) with various additives terface formation between Ag and ZnO/CdO (Necker, among the many other choices such as Ag-Ni, Ag-Cu, 1988). The quantitative results will be presented along Ag-Pd, Ag-Fe, Ag-Au, etc (Frederic Pons, 2010). with microstructural analyses. The Korea Institute of Industrial Technology (KITECH) is currenly develping a Cd-free (Ag-Cu-Fe)-Sn/Zn alloy References system to form SnO2 or ZnO via internal oxidation pro- Brainin Company (2015): Electrical Contact Mate- cess to replace CdO. A minor addition of Cu and/or Fe rials List in the Technical Resources. http://www. is designed to reduce Ag for an econocmical reason. In pepbrainin.com/technical-resources/electrical-con- order to increase surface wear resistance, shot peend- tact-materials. ing process was applied, which is also expected to af- Pons, F. (2010): Electrical Contact Materials Arc Ero- fect the depth of oxidation layer. sion: Ph.D. Thesis, Georgia Institute of Technology, Focusing on characterization of the mechanical proper p 8-11. ty of the electrical contact materials, two kinds of alloy Noyan, I. C., and Cohen, J. B. (1987): Residual Stress, systms have been tested: Ag(88)-Cu(1)-Fe(1)-Zn(10), Springer-Verlag, New York, NY, p 117-125. and Ag(90)-Cd(10) reference. Thermal oxidation and Necker, G. and Mader, W. (1988): Characterization of shot peending processes were selectively applied for Ag/CdO interfaces: Philosophical Magazine Letters, 58, both alloys, and micro vickers, X-ray diffraction, and 4, p 205-212. Structural phase states and residual stresses in the Ta/TiNi surface layers before and after high-current pulsed electron beam impact L.L.Meisner1,2, M.G.Ostapenko1, 3, M.A.Zakharova3, E.Yu.Gudimova1,2 1 Institute of Strength Physics and Materials Science of Siberian Branch Russian Academy of Sciences, Tomsk, Russia 2 Tomsk State University, Russia 3 Tomsk Polytechnic University, Russia be used coating of tantalum, which have good biocom- It is known that NiTi based alloys are widely used in patibility. To improve the adhesion strength of the tan- medicine. There is a problem release of nickel ions, talum coating to the NiTi substrate can be used elec- which is potentially dangerous. As barrier coatings can tron beam impacts. Apparently, the surface properties 373 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 of NiTi alloy with tantalum coating after electron beam Analysis of the depth distribution of the chemical el- impacts are defined by the structural phase state and ements in Ta/NiTi samples, obtained by AES, showed residual stress in its modified surface zone. that, between the coating and the substrate, there is a Therefore, the aim of this work is to study the forma- transition layer (~400 nm) containing 8 ÷ 20 at.% Oxy- tion of structural-phase states and residual stresses gen and ~ 8 at.% Carbon, that can lead to the formation in the tantalum coatings and based on NiTi, and their therein of oxide and carbide phases and decrease the changes after impacts with pulsed electron beams. adhesive strength of Ta coatings with substrate. The As the initial samples was used alloy NiTi, which treatment by LEHCPEB led to forming on the surface were characterized by a two-phase state (~95 vol.% of NiTi uniform layer consisting mainly of Ta with no В2+~5 vol.% Ti2Ni). Magnetron sputtering was carried clearly defined boundaries between the coating and out at the facility KVANT-M. The coating thickness was the NiTi substrate was formed. We can assume that in about 400 nm (hereinafter – Ta/NiTi). The Ta/NiTi spec- the surface layer of the samples Ta/TiNi after LEHCPEB imens were subjected to pulsed surface irradiation by a as a result of partial dissolution of tantalum atoms in low-energy high-current electron beam (LEHCPEB). The NiTi was formed ternary phase based on (TiNi) –Ta with beam energy density was Е = 15 J/cm2 . X-ray diffraction B19’ martensite structure [1]. (XRD) analysis was performed at room temperature on Comparison of the results of quantitative evaluation of a DRON-7 diffractometer. the residual stress in the surface layers Ta/TiNi samples It was found that after the deposition of Tantalum coat- before and after electron-beam impacts showed that ing on the X-ray diffraction pattern of samples the ab- after modification, the amount of residual stress in B2 sence of peaks of the Ti2Ni phase and new reflexes cor- phase in the surface layer of the samples was not sig- respond to bcc α-Ta (space group Im3m) and tetrago- nificantly increased. nal β-Ta (space group P42/mnm) phases are observed, with the prevalence of the α-Ta phase (~ 65 vol.%). Reference Interpretation of the X-ray pattern of the sam 1. Gong C.W., Wang Y.N., Yang D.Z. Phase transforma- tion and second phases in ternary Ni–Ti–Ta shape ple Ta/NiTi after LEHCPEB shows that the new peaks memory alloys // Materials Chemistry and Physics, correspond to the B19′ martensite phase with mono- 2006. – V. 96. – P. 183–187. clinic structure (space group P21/m). The effect of residual stresses on the change of the B2 phase lattice parameter in the NiTi with Tantalum coating after pulsed electron-beam treatment M.G. Ostapenko1, 2, L.L. Meisner1,3, M.A. Zakharova2, E.Yu. Gudimova1,3 1 Institute of Strength Physics and Materials Science of Siberian Branch Russian Academy of Sciences, Tomsk, Russia 2 Tomsk Polytechnic University, Russia 3 Tomsk State University, Russia Nickel titanium is widely used as material for medical The aim of this work is to study residual stresses fields’ application due to shape memory effect and superelas- evolution in the near-surface layers of NiTi with tanta- ticity. High requirements were claimed on the alloy in lum coating, irradiated with electron beam of 15 J/cm2 regard to its biocompatibility and corrosion resistance energy density. [1]. One of the ways to improve these properties is the The investigation of structure-phase states and the biocompatible coatings deposition. Highly attractive estimation of residual stresses were performed using metal to apply is tantalum, but coating formation re- X-ray diffraction analysis, which allows determining lat- quires taking into account the surface texture of NiTi tice and elastic constants both. Symmetric and asym- may change because of martensitic transformation. metric scanning schemes were applied to study the This can lower the adhesive strength of coating. Ad- structure in the bulk and near surface layers. hesion can be improved by low energy high current Initial sample was made of alloy, melted from iodide pulsed electron beam treatment (LEHCPEB). titanium and NO-grade nickel (Ti49.5Ni50.5), and then Residual stresses can be formed as a result of LEHCPEB coating with thickness of 400 nm was deposited by not only in the area of direct irradiation, but also in the magnetron sputtering. The sample under study was in layers below. The presence of residual stresses leads to three-phase state at room temperature: phase B2 (bcc the significant change of functional properties of NiTi structure, CsCl ordering) of substrate, α-Та (bcc, space alloys [2]. group Im3m) and β-Ta (tetragonal, space group P42/ 374 Poster Topic B: Mechanical Behaviour mnm) phases of coating. It was revealed phase β-Ta Thus, analysis of obtained results have shown, that disappeared after LEHCPEB treatment due to rapid LEHCPEB treatment with energy density of 15 J/cm2 quenching (~109 K/s) of the near surface layer of the for samples with coatings leads to partial coating re- sample. Peaks of martenisitic phase B19’ was found tention, B19’ martensitic phase and significant residual while analyzing diffraction patterns of irradiated sam- stress values appearance. ple. For sample, treated with LEHCPEB, it was revealed References that lattice parameter of B2 phase has changed from [1] Cheng Y., Cai W., Li H.T., Zhao C. (2003): Corrosion 3.0108 up to 3.0247 Å. That might be related to the property of TiNi shape memory alloys coated with presence of significant residual stresses. tantalum. – Journal of Material Science, 1681-1683; Quantitative estimation comparison for initial and irra- Harbin. diated samples shown LEHCPEB treatment causes sig- [2] Meisner L.L., Lotkov A.I., Ostapenk M.G. Gudimova nificant change in residual stresses’ values from ~145 E.Yu. (2012): X-ray diffraction study of residual elas- MPa up to ~540 MPa for B2 phase in the near-surface tic stress... - Physical Mesomechanics, 79-89; Tomsk. layer. Laser assisted residual stress determination in ceramic coatings Peter Weidmann1, Giancarlo Pedrini2, Venancio Martínez-García3, Ulrich Weber1, Andreas Kill- inger3, Martin Wenzelburger3, Siegfried Schmauder1, Rainer Gadow3, Wolfgang Osten2 1University of Stuttgart, IMWF, Germany 2University of Stuttgart, ITO, Germany 3University of Stuttgart, IFKB, Germany Technical compounds under high thermal and abrasive measurements in consideration for the inhomogene loads are often coated to enhance the materials wear ous elastic material properties and deviations from resistance and thermal durability. Therefore, ceramic cylindrical hole geometry. To cover all involved fields coatings with high hardness and low thermal conduc- numerical studies for conventional hole drillings with tivity are preferable. Such coatings may be produced differential and integral determination schemes were by i.e. plasma or high velocity oxygen fuel spraying. conducted and the ablation process was simulated. As But due to quenching of splats and differences in the the laser cannot produce ideal cylindrical geometries thermal properties of substrate and coating, residual appropriate mathematical approximations by means of stresses will build up. These stresses can lower the life- least square optimisation are used to choose a repre- time of the coated product or even enhance it in the sentative hole profile. Furthermore, the calculation of case of pressure stresses within brittle ceramic layers. stress based on full field displacement measurements A convenient way to determine such residual stresses is done with an own developed program in several are incremental hole drilling measurements. Hereby, depth increments. These calculations are based on nu- a hole is drilled incrementally into the stress afflicted merical calibration data for the elastically inhomogene- material. This leads to a relaxation of surrounding ma- ous compound of coating and substrate. The physical terial. The hereby occurring surface strains around the experiments were done on aluminium and steel plates hole can be measured with strain gauges and trans- with applied aluminium- or aluminium-titanium-oxide ferred into the depth dependent residual stress. But layers. The coatings have been made by atmospheric this method implies direct contact with the specimen plasma spraying up to a thickness of 200 µm. and the preparation of strain gauge rosettes which leads to a rather time consuming process especially References for incremental drilling procedures. To overcome these Weidmann, P. & Weber, U. & Schmauder, S. & Ve- constraints a method is wanted where the drilling is nancio Martínez-García (2014): Investigation of done by a laser and the occurring surface deformations Influence Factors on Residual Stress Determination are recorded by digital holography measurements. within Coated Surfaces in Consideration of the Dif- Therefore, new approaches and extension of known ferential and Integral Method – In: Advanced Mate- procedures are required to determine residual stresses rials Research 996: 307-312. contact-free with the imposed method. Schajer, G. S. & Steinzig, M. (2005): Full-field calcula- The presented work is related to the underlying as- tion of hole drilling residual stresses from electronic sumptions and calculations to determine the depth speckle pattern interferometry data – In: Experi- dependent stress values from extensive displacement mental Mechanics 45-6: 526-532. 375 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Poster Topic C: Cyclic deformation behavior, crack initiation & crack growth of metals 376 Poster Topic C: Cyclic deformation behavior, crack initiation & crack growth of metals Fatigue crack initiation from notches and mean stress effect in 2024 T351 Al-alloy Mustapha Benachour1, Nadjia Benachour1,2, Mohamed Benguediab3 1IS2M Laboratory, Mechanical Engineering Department, University of Tlemcen, Algeria 2Physics department, Faculty of Sciences, University of Tlemcen, Algeria 3 LMSR Laboratory, Mechanical Engineering Department, University of Sidi Bel Abbes, Algeria Fatigue phenomenon presents an essential failure The aim of this work is to present mean stress effect on mode in aircraft structures. The percentage of failure fatigue crack initiation in 2024 T351 Al-alloy used in air- varies from 55 to 61% in Aeronautic components. Crack craft components. In this investigation, fourth bending initiation due to various defects presents the main in- fatigue tests were carried out to evaluate evolution in vestigation of aircraft components. The initiation of fatigue initiation life from V-notches. A fatigue criteri- crack is essentially attributed to machining defects and on was established to predict crack-initiation at the tip to the concentration of stress at notch. of a V-notch. Best correlation of present criterion was given comparatively to others results for same material and stress ratio. Resonant acoustic for nondestructive inspection of accumu- lated damage assessment in austenitic stainless steel sub- jected to fatigue tests in rotating bending Ricardo A. Casali1, Maria A. Caravaca2, Cesar G. Veroli3,Gabriel Vallejos3, Jorge Forte2 1Departamento de Física. Facultad de Ciencias Exactas, Naturales y Agrimensura, Corrientes, Argentina 2Departamento de Físico-Química. Facultad de Ingeniería, Resistencia. Argentina 3Departamento de Mecánica. Facultad de Ingeniería, Resistencia, Argentina In this work we study by resonant inspection the dam- References age that may accrue to the specimens, subjected to fa- R.A. Casali et al http://www.ndt.net/article/pan- tigue tests using the method of Staircase. The resonant ndt2007/papers/109.pdf inspection shows enlargements (damping factor) and ASTM Standard E2001-08, Standard Guide for Reso- frequency shifts of resonance peaks of bending and nant Ultrasonic Spectroscopy for Defect Detection longitudinal modes, indicating greater plasticity with in Both Metallic and Non-metallic Parts. respect to the initial state, without fatiguing. In the G. Stultz, R. Bono and M. Schiefer, “Fundamentals of failed specimens crack and its position is recognized by Resonant Acoustic Method NDT”,www.modalshop. identifying bending mode resonances (F1, F2, F3, F4) com and longitudinal (L1). Specimens of steel „did not fail“ Suheng-Kuei lin, Yung-Li lee, Ming-Wei Lu, “Evaluation are tested again with a stress level below the fatigue of the staircase and accelerated methods for fatigue limit. These are used to study, after further cyclized limit scheduled, based on applying the theory Miner of cu- distributions”, International Journal of fatigue, Vol 23, mulative damage. These studies are complemented by (2001) 75-83 metallographic and hardness tests at different points Man, X. T. C., Wang, Z., and Finch R. D., “Vibration of specimens used in tensile tests, notched fatigued monitoring of steel beams by evaluation of reso- and without fatigue. nance frequency decay rates”, J. Acoust. Soc. Am. 96 (2), 867-873 (1994). 377 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Determination of the Crictical Resolved Shear Stress in a Ni- Al-Cr composite by Discrete Dislocation Dynamics Herve Gakam1, Daniel Weygand2 1KIT Karlsruhe Institut of Technology, IZBS, Germany 2KIT Karlsruhe Institut of Technology, IZBS, Germany Within the research program IMD www.imd.kit.- edu) tates taking in consideration the variation of the length a new high temperature superalloy shall be developed. L and Diameter D of the fibers are produced on the ba- The microstructure consists of a NiAl matrix [1], which sis of the experimental received data and used in the alone has poor mechanical properties at high tempera- simulation set up [4]. tures, and Cr fibers, which block the motion of dislo- It is observed that, with increasing irregularity the CRSS cations within the NiAl matrix and increase the creep as their spread in the obtained increases. Furthermore resistance significantly. The microstructure is obtained the effect of the elastic interaction between multiple by solidification at the eutectic composition for the ter- dislocations on parallel planes gliding through this ob- nary system and under ideal conditions long Cr fibers stacle field shall be addressed. At the end the softening are expected [2, 3]. In a two dimensional Cross-section effect at the boundary interface between Cr fibers and with the normal parallel to the Cr fibers axis a close NiAl matrix doing to lattice mismatch is investigated to hexagonal arrangement of the fibers cross-sec- and it was found that the CRSS decrease in this case for tions is observed. In order to determine the Critical non shearable fibers of about 20%. Resolved Shear Stress (CRSS) for a dislocation passing through this almost hexagonally arranged obstacle References field discrete dislocation dynamics (DDD) simulations [1] R. R. Bowman, R. D. Noebe et al., metall. Trans. are performed [2, 5]. The role of the irregularities in V23A p.1493, 1992 the arrangement and the fibers diameters in the ex- [2] Walter, J.L. and Cline, H.E. Metal. trans. volume perimentally measured microstructures is explored by 1, p. 1221, 05.1970 a systematical variation of the obstacle distribution in [3] M. Heilmaier, T. Haenschke1 , A. Gali, M. the simulations. The simulations use periodic bound- Krueger , H. Bei, E.P. George, J. Phys.: Conf. Ser. ary conditions to eliminate surface effects and the fi- 240 012063, 2010 bers are treated in this first step as non-shearable and [4] Bako, B. and Weygand, D. and Samaras, M. and those bypassing occurs by the Orowan mechanism. In Hoffelner, W. and Zaiser, M. Phys. Rev. B, v.78 order to determine the CRSS valid for this superalloy p. 144104, 2008 the length L between two centers of Cr fibers is varied. [5] D. Weygand, modell. Sim. Mater. Sci. Eng. vol. Furthermore several distributions of the Cr precipi- 10, pp. 437 - 468, 2002 Cyclic softening in the MA956 ODS steel ivo kubena1, jaroslav polák1, tomáš kruml2 1Institute of Physics of Materials, Brno, Czech Republic 2CEITEC IPM, Brno, Czech Republic High chromium steel (MA956) prepared by mechanical tening was followed by relatively long stage where alloying (MA) and strengthened by fine oxide disper- the softening rate is constant and lower than the one sion was investigated. Corse microstructure with grains measured in the first stage. In last stage, cyclic soften- larger than 100 µm was revealed. The oxide distribu- ing rate again increases, but this rather influenced by tion was analyzed by the means of transmission elec- the growth of long cracks. tron microscopy. Specimens were cycled with constant Cyclic softening and role of oxide dispersion was dis- strain amplitude and strain rate at room temperature. cussed in relation with microstructural observations. Continuous cyclic softening consisting of three stages Moreover, microstructure and cyclic softening of the was measured. Short initial stage of rapid cyclic sof- MA956 steel is compared with different ODS steels 378 Poster Topic C: Cyclic deformation behavior, crack initiation & crack growth of metals Influence of pre-strain on fatigue crack growth behavior in rolled AZ31 magnesium alloy Ryoichi Momoe1, Shigeki Morita2, Tsuyoshi Mayama3, Nobusuke Hattori2 1Graduate Student, Department of Science and Engineering, Saga University, Japan 2Department of Mechanical Engineering, Saga University, Japan 3Organization for Innovation and Excellence, Kumamoto University, Japan It is well known that the {10-12} deformation twin to the short transverse direction. Pre-tensile plastic is ocuured as tension is applied parallel to the c axis strains were generated at 1% , 2%, 3% with a mechan- for magnesium alloys [1]. Hong et al. [2] showed that ical testing machine. The pre-strained specimens were the compressive deformation along the rolling direc- defined as 1% pre-strained, 2% pre-strained, 3% pre- tion yielded at much lower stress as compared to the strained, respectively. FCP tests were performed at a tensile deformation and the exactly reversed features stress ratio of R=0.1 and a frequency of 10 Hz at room were observed for the nomal direction. Shiozawa et al. temperature. The fracture surfaces were observed by [3] claimed that the step-wise S-N curve was induced SEM. by the crack initiation mechanism changing from the The FCP rate of the S-T specimen showed higher than twin deformation in high-stress amplitude level to slip that of the L-T and the L-S specimens. The FCP rate de- deformation in low-stress amplitudes. Recently, Huang pends on the texture. The FCP rate of the pre-strained et al. [4] suggested that in rolled AZ31 magnesium alloy specimens showed lower than that of the undeformed by pre-compression deformation, the deformed sam- S-T specimen. The FCP rate of the 2% pre-strained ples showed much longer fatigue life than the as-rolled specimen was lowest in the examined pre-strained sample. The aim of present study is to investigate the specimens. Compared with the fracture surface of the influence of twin deformation on fatigue crack growth undeformed specimen, much lines and bigger steps behavior in rolled AZ31 magnesium alloy. were observed in that of the pre-strained specimens. It Material used in the present study is commercial rolled is suggested that the existence of {10-12} deformation AZ31 magnesium alloy. Basal planes are aligned par- twin at a crack tip might interfere crack propagation allel to rolling direction. A mean grain size of approx- and make FCP rate lower. imately 38 µm. Tensile 0.2% proof stress is 129 MPa parallel to the rolling direction and 53 MPa parallel to References the short transverse direction. The fatigue crack prop- [1] Barnett, M. R. (2007): Twinnig and the ductility of agation (FCP) specimens with width 12 mm, thickness magnesium alloys Part 1: “Tension“ twins – Mater. 4 mm, initial slit length 1 mm were machined from the Sci. Eng. A 464, 1-7. plate. The specimen which loading axis is parallel to [2] Hong, S. G. et al. (2010): Anisotropic fatigue be- the rolling direction; fatigue crack propagated parallel havior of rolled Mg-3Al-1Zn alloy – J. Mater. Res. 25, to the transverse direction is defined as the L-T spec- 966-971. imen. The specimen which loading axis is parallel to [3] Shiozawa, K. et al. (2010): Fatigue behaviour and the rolling direction; fatigue crack propagated parallel fractography of extruded AZ80 magnesium alloys to the short transverse direction is defined as the L-S in very high cycle regime – Procedia Engineering 2, specimen. The specimen which loading axis is parallel 183-191. to the short transverse direction; fatigue crack propa- [4] Huang, G. et al. (2014): Improving low-cycle fa- gated parallel to the transverse direction is defined as tigue properties of rolled AZ31 magnesium alloy by the S-T specimen. In order to introduce {10-12} defor- pre-compression deformation – Materials and De- mation twin, the S-T specimens were loaded parallel sign 58, 439-444. 379 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Anisotropy of cyclic deforrmation and fatigue properties in rolled AZ31 magnesium alloy Shigeki Morita1, Ryota Ikeda1, Tsuyoshi Mayama2, Nobusuke Hattori1 1Saga University, Japan 2Kumamoto University, Japan Magnesium alloys are the lightest structural material for the S-specimen. The fatigue strengths at 107 cycles with a high strength-to-weight ratio. These features of the L- and S-specimens were 80 MPa and 60 MPa, make magnesium alloys attractive for applications in respectively. The fatigue strengths were similar to the the automotive and aircraft industry. Wrought Mg-Al- monotonic compressive or tensile 0.2% proof stresses Zn system alloys are suitable candidates for structural for both specimens. Stress-strain hysteresis loops were parts. It is important to elucidate the cyclic loading be- linear in tensile and compressive phases at the lower havior and fatigue properties of the material used for stress amplitude of fatigue strength and the compli- structural parts. cated elastic-plastic-pseudoelastic deformations were It is well known that wrought magnesium alloys have observed in tensile and compressive phases at the a hexagonal close-packed (HCP) structure, and strong higher stress amplitude of fatigue strength of load-con- textures are formed by rolling and extrusion. Basal trolled axial fatigue test. Tensile mean strain generated planes are aligned parallel to the rolling direction by by cyclic elastic-plastic-pseudoelastic deformations at rolling. Depending on their microstructure, magne- the higher stress amplitude of fatigue strength for the sium alloys show unique deformation behavior such as S-specimen. The deformation twins were observed in mechanical anisotropy (Chino et al. 2008), pseudoelas- the specimen subjected to the higher stress amplitude ticity in loading-unloading (Ca´ceres et al. 2003), and of fatigue strength and free deformation twins were asymmetricity of stress-strain hysteresis loops in strain observed in the specimen subjected to the lower stress controlled low-cycle (Hong et al. 2010) and load con- amplitude of fatigue strength. trolled high-cycle (Morita et al. 2010) fatigue tests. To investigate the anisotropy of cyclic deformation and References fatigue properties, cyclic compressive and tensile load- Chino, Y., Kimura, K., Hakamada, M. & Mabuchi, M. ing-unloading tests were carried out using cylindrical (2008): Mechanial anisotropy due to twinning in smooth specimens of rolled AZ31 magnesium alloy. an extruded AZ31 Mg alloy - Mater. Sci. and Eng. A, Load-controlled axial fatigue tests were also carried 485: 311-317. out with smooth specimens attached on strain gages Ca´ceres, C. H., Sumitomo T. & Veridt M. (2003): Pseu- at specified stress amplitudes levels. Monotonic ten- doelastic behavior of cast magnesium AZ91 alloy sile and compressive 0.2% proof stresses of the L-spec- under cyclic loading-unloading - Acta Mater., 51: imen (loading axis is parallel to Longitudinal direction) 6211–6218. were 129 MPa and 78 MPa, respectively. On the other Hong, S.G., Park, S.H., Huh, Y.H. & Lee, C.S. (2010): hand, monotonic tensile and compressive 0.2% proof Anisotropic fatigue behavior of rolled Mg-3Al-1Zn stresses of the S-specimen (loading axis is parallel to alloy - J. Mater. Res., 25: 966-971. Short-transverse direction) were 53 MPa and 85 MPa, Morita, S., Tanaka, S., Ohno, N., Kawakami, Y. & Enjoji, respectively. Pseudoelastic behaviors were observed T. (2010): Cyclic Deformation and Fatigue Crack Be- in compressive and tensile loading-unloading tests for havior of Extruded AZ31B Magnesium Alloy – Mater. L- and S-specimens. The larger anelastic strains were Sci. & Forum, 638-642: 3056-3061. observed in compressive stress-strain hysteresis loops 380 Poster Topic C: Cyclic deformation behavior, crack initiation & crack growth of metals Fatigue properties of fine-grained AZ31 magnesium alloy Yuji Okamoto1, Takahito Hori1,Shigeki Morita2, Hidetoshi Somekawa3, Tsuyoshi Mayama4, Nobusu- ke Hattori2 1 Graduate student, Department of Mechanical Engineering, Saga University, Japan 2 Department of Mechanical Engineering, Saga University, Japan 3 Research Center for Strategic Materials, National Institute for Materials Science, Japan 4 Organization for Innovation and Excellence, Kumamoto University, Japan Magnesium alloys are the lightest structural material, ing machine (capacity: 9.8 kN) in laboratory air at room and have higher strength-to-weight ratio than steel temperature, at frequency of 10 Hz and stress ratio of and aluminium alloy. These features make magnesi- 0.1. Crack initiation and small crack growth were mon- um alloys attractive for applications in the automotive itored with replication technique. components, e.g. steering wheel frame and gear box Mechanical properties of fine-grained alloy, e.g. tensile housing1). It is important to investigate cyclic loading and compressive strength and fracture strain show su- behavior and fatigue properties of the material used perior to the coarser-grained AZ31 magnesium alloys. for structural parts. The ratio of 0.2% proof stress was σ0.2compression/σ0.2tension= In the case of magnesium alloys, deformation twins (193/209)= 0.92. Compared with coarser-grained al- easily form when coarse-grained alloy is subjected to loys, the mechanical anisotropy of fine-grained alloy compressive stress in loading direction parallel to ex- was improved. Fatigue strength of fine-grained alloy trusion2,3). This behavior causes lower compressive was σmax= 170 MPa. The fatigue crack initiated at 39% yield strength compared with tensile one for extruded of total fatigue life. The fatigue crack initiated at the alloys4,5). It is known that twinning can be essentially interface between the inclusion and the matrix. The reduced by grain refinement. The mechanical property fatigue crack propagation rate was similar as the other and anisotropy of magnesium alloys were significantly coarse-grained alloys at stress ratio of 0.1. As the re- improved by grain refinement4). However, the fatigue sults, fatigue crack initiation can be improved by grain property in fine-grained magnesium alloy is far from refinement, however, fatigue crack propagation was fully understood. This paper presents fatigue strength slightly influenced by grain refinement. and fatigue crack initiation and propagation behavior of fine-grained extruded AZ31 magnesium alloy. References AZ31 (Mg-3%Al-1%Zn) magnesium alloy with a thick- Mordike, B. L. and Ebert, T. (2001): Magnesium Prop- ness of 5 mm was extruded at temperature of 473 K. erties - applications - potential - Mater. Sci. Eng. A, Subsequently, the alloys were annealed at 423 K for 302 : 37-45. 86.4 ksec. The texture exhibits the combined features Wang, J. T., Yin, D. L., Liu, J. Q., Tao, J., Su Y. L. and of the typical rolling and extrusion textures. The aver- Zhao, X. (2008): Effect of grain size on mechanical age of the grain size was 2.5 µm. Tensile and compres- property of Mg-3Al-1Zn alloy - Scri. Mater, 59: 63- sive specimens were machined from the annealed bar. 66. Loading axis was parallel to the extrusion direction. Barnett, M.R., Keshavarz, Z., Beer, A.G. and Atwell, D. The tensile and compressive tests were performed on (2004): Influence of grain size on the compressive an mechanical testing machine at a crosshead speed deformation of wrought Mg-3Al-1Zn - Acta Mater., of 8.3*10-6 m/s in laboratory air at room temperature. 52: 5093–5103. Fatigue specimens with gage length of 10 mm, a width Chino, Y., Kimura, K., Hakamada, M. and Mabuchi, M. (W) of 5 mm, a thickness (t) of 4 mm were machined (2008): Mechanical anisotropy due to twinning in from the annealed bar. SENT (Single Edge Notched Ten- an extruded AZ31 Mg alloy - Mater. Sci. and Eng. A, sion) specimens with a width (W) of 12 mm, a thick- 485: 311-317. ness (t) of 4 mm, an initial slit length (a) of 2 mm, and a Somekawa, H., Maruyama, N., Hiromoto, S., Yamamo- length (L) of 50 mm were machined from the annealed to, A. and Mukai, T. (2008): Fatigue Behaviors and bar. The axial fatigue tests and fatigue crack propaga- Microstructures in an Extruded Mg-Al-Zn Alloy – tion tests were performed on an electro-hydraulic test Mater. Trans., 49: 681-684. 381 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Dwell effects on low cycle fatigue behaviour of diffusion coated nickel base superalloy IN 713LC at temperature of 800°C Ivo Šulák1, Karel Obrtlík1, Simona Hutařová2, Martin Juliš2, Tomáš Podrábský2, Ladislav čeklko2 1Institute of Physics of Materials, AV CR, Brno, Czech Republic 2Brno University of Technology, CEITEC, Czech Republic Materials used for high temperature applications such age pores. Microstructure is formed by γ matrix with γ´ as disks, blades and vanes of gas turbine engines re- strenghtening precipitates, carbides and eutectics. quire exceptional resistance to mechanical and ther- Polycrystalline diffusion Al-Cr coating was prepared mal loading as well as against chemical attacks by ox- by a Cr modified aluminizing using the chemical vapor idation, which significantly increases with operating deposition (CVD) out of pack process. The coating was temperature. First generation Ni-base superalloy IN deposited in two-steps: 1050 °C/5h and 950 °C/5h. Mi- 713LC developed by the International Nickel Compa- crostructure of the Al-Cr layer comprises an outer layer ny in the 1950s is the representative of cast materials and an inner diffusion layer with dispersion of a large used for these purposes, especially because of favor- amount of complex particles based on Cr, Mo and Nb. able price in conjunction with satisfying high tempera- For purpose of this work cylindrical specimens were ture properties. However, the continuous enhancing of machined from the rods manufactured using invest- operating temperature severely degrades the material ment castings technique. Low cycle fatigue tests and surface and adversely affects the strength properties tests with 10 minute tensile dwells included in each and component life. Protection of the surface and cycle were conducted in strain control mode with con- prevention of its degradation is a major goal of today stant total strain amplitude and strain rate at 800 °C and tomorrow. Diffusion coatings are primarily used to in air. safeguard the material from aggressive environments The fatigue behaviour was characterized by cyclic and to improve corrosion and oxidation stability of hardening/softening curves, cyclic stress-strain curves, surface. Nowadays, superalloy surface is enriched with Manson-Coffin curves and Basquin curves. The sub- appropriate oxide formers such as aluminum and other strate and the Al-Cr coating were examined in as-re- elements (Cr, Si..). ceived conditions and also after cyclic loading by The topic of the present paper is focused on the means of optical microscopy, SEM and energy disper- study of low cycle fatigue with tensile dwells of cast sive spectroscopy (EDS). Micro-hardness depth profile nickel-base superalloy IN 713LC with Al-Cr difussion was obtained with the Knoop indenter. The fracture coating at 800 °C. Increased attention is paid to the surface observation, changes in microstructure and in- microstructure observation of the substrate material vestigation of polished section parallel to the specimen and Al-Cr diffusion layer. Macrostructure of IN 713LC axis help to discuss the mechanisms operating in fa- consists of coarse dendritic grains whose average size tigue degradation of surface treated superalloy in both was determined to 2.4 mm ± 0.5 mm and some shrink regimes of cycling. 382 Poster Topic D: In-situ microscopy and diffraction Poster Topic D: In-situ microscopy and diffraction 383 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Strain induced martensitic Transformation in Austempered Ductile Iron (ADI) Xiaohu Li1, Patrick saal2, Michael hofmann1 , Markus hölzel1 1 Forschungs-Neutronenquelle FRM II, Technische Universität München, Germany 2 Institute of metal forming and casting, Technische Universität München, Germany Austempered ductile iron (ADI) is a nodular ductile plastic strains. In addition texture measurements using iron which has undergone a special heat treatment neutron diffraction have been performed to calculate to greatly enhance mechanical properties. The heat the texture distribution of ferrite and austenite phas- treatment process of ADI consists of austenitization, es for different strain levels. Combining the detailed quenching to a temperature typically between 250°C information on texture with the in-situ studies is nec- and 450°C and isothermal austempering [1]. After such essary for quantitative phase analysis and extraction of heat treatment the microstructure consists of acicular martensite phase fractions. ferrite and high carbon enriched retained austenite. The results of these experiments allows us to illustrate The microstructure of ADI strongly depends on the the martensitic transformation kinetic in ADI with aus- austenitizatin and austempering temperatures. Details tempering temperature, alloy element Nickel and plas- on dependence of microstructure and temperature tic strains. can be found in [1, 2]. In industrial applications alloy- ing elements such as Ni, Mn or Cu are used in order to References delay the phase transition kinetics, which improves the [1] Leopold Meier, Michael Hofmann, Patrick Saal, austemperability of thicker geometries. Wolfram Volk, Hartmut Hoffmann, Materials Char- The high carbon enriched retained austenite can trans- acterization 85 (2013) 124-133 form to martenite during plastic deformation. Four dif- [2] Miguel Angel Yescas-González, Modelling the ferent treatment parameters (austenitization temper- microstructure and mechannical properties of aus- ature, austempering temperature, austempering time tempered ductile iron, Dissertation in department and alloying composition) can influence the retained of materials science and metallurgy, University of austenite fraction, grain size and its stabilisation [3],[4], Cambridge, (2001) which in turn will influence the following martensitic [3] Srinivasmurthy Daber, K. S. Ravishankar and P. transformation. Prasad Rao, J.Mater.Sci (2008) 43:4929-4937 The influence of different treatment and composition [4] C. Capdevila, F. G. Caballero and C. García de An- parameters on the martensitic transformation have drés; Analysis of the effect of alloying elements on beeninvestigated using in-situ neutron diffraction dur- the martensite-start temperature of the steels; De- ing applying either tension or compression to different partment of Physical Metallurgy, CENIM An in situ experimental method for evaluating the tensile property of single crystalline gold nanorod Yabin Yan1, Xiaoyuan Wang1, Takashi Sumigawa2, Takuya Nakano2, Takayuki Kitamura2 1Institute of Systems Engineering, China Academy of Engineering Physics, Mianyang, China 2Department of Mechanical Engineering and Science, Kyoto University, Kyoto, Japan The mechanical properties of submicron- or nanoscale also been performed; however, this method can not materials are of practical importance because they are yield fracture properties. Thus, tensile experiments are used in interconnections above semiconductor layers desired, because of the uniform stress distribution as in ultra-large-scale integrated circuits. The mechanical well as the ability to obtain fracture behavior at large properties of submicron- and nanoscale materials are strains. different from those of the bulk because of the small In this wrok, we develop a new in situ experimental volumes of the former. Although bending and nano-in- method for evaluating tensile properties of nano-ma- dentation tests have examined the size effects in plas- terials and apply it to a single crystalline gold nanorod ticity (McElhaney et al. 1998), severe strain gradients with a square section of 189 nm × 189 nm. The nano- exist in the specimens. Micro- or nanoscale pillar com- rod, which is carved out of a bulk material by focused pression experiments (Dimiduk et al. 2005, Uchic et ion beam processing, is mounted on a lozenge-shaped al. 2005) where the strain gradients are minimal have silicon frame and is pulled by a compressive load ap- 384 Poster Topic D: In-situ microscopy and diffraction plied onto the top face of the frame. Although the References applied load increases linearly in the early stages of Dimiduk, D. M., et al. (2005): Size-affected single-slip deformation, it drops rapidly at a certain displacement. behavior of pure nickel microcystals. Acta Material- In-situ TEM observations indicate that the rapid drop is ia, 53, 4065-4077. induced by the crystallographic slip generation within McElhaney, K. W., et al. (1998): Determination of the nanorod. The critical resolved shear stress on the indenter tip geometry and indentation contact area active slip system at yielding is evaluated to be 325.8 for depth-sensing indentation experiments. Journal MPa, which is almost 600 times larger than that of the of Materials Research, 13, 1300-1306.. bulk counterpart. The high critical resolved shear stress Uchic, M. D., et al. (2005): A Methodology to Investi- is due to the low dislocation density in the nanorod. gate Size Scale Effects in Crystalline Plasticity using When the tensile elongation becomes large, the nano- Uniaxial Compression Testing. Materials Science and rod shows necking and isotropic plastic behavior inde- Engineering A, 400–401, 268–278. pendent on the crystalline structure. 385 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Poster Topic E: Size effects and small-scale mechan- ical behavior of materials 386 Poster Topic E: Size effects and small-scale mechanical behavior of materials Indentation Size Effect of Nanoporous Gold: Correlated by Unique Structure and its Size-Dependent Mechanical Behavior Seung-min Ahn, young-Cheon Kim, and Ju-Young Kim School of Materials Science & Engineering, UNIST (Ulsan National Institute of Science and Technology), Korea Nanoporous gold (np-Au), a low density open-cell euqal to yield strength because of the underneath the structure material with ligaments and pores, has been indenter is not constrained by the surrounding materi- studied as attractive candidates in various applications als. For this reason, we intended to discuss ISE and to such as sensor, catalyst, and actuator due to high sur- characterize mechanical properties of bulk np-Au spec- face-to volume ratio that combined with chemical and imens. We prepared np-Au specimens with ligament electrical properties of gold. In addition, one of the diameters of 20 through 150 nm which was fabricated merits on np-Au is simply fabricating using dealloying by free corrosion dealloying process. The ligament dia- method that, based on Ostwald ripening, is used to re- menters are cotrolled by dealloying conditions such as move a sacrificial element of Ag from a precursor alloy, temperature and concentraion of nitric acid solution. Au-Ag alloy, which is followed by surface diffusion of We estimated the mechanical properties of np-Au hav- Au and aggrogation of Au adatoms into clusters that ing variable ligament size using nanoindentation and form the interconnected ligaments of the nanoporous uni-axial compressive test. And then combined it for structure. For using various application, estimation of establish its correlation. To confirm deformation be- mechanical behavior of np-Au is a priority. According to havior of underneath the indenter we used FIB milling several researches, the mechanical properties of foams as residual indent marks and observed plastic collapse, were evaluated by nano-indentation with scaling equa- densification, using cross-sectional SEM images. This tions basis on the basis of foam relative density. Fu- makes it possible to discuss additional factor of ISE in thermore, recent experimental results on np-Au have porous materials. We discussed ISE of np-Au in terms shown a rapid increase in hardness with decreasing in- of densification of specimen, and suggested optimized dentation depth, so-called indentation size effect (ISE). modeling of ISE in np-Au excluded of effect of GNDs. In the case of fully dense materials, ISE is observed up to 103 nm of indentation depth, and underlying prin- References ciple was revealed Nix and Gao that increase in the Gibson, LJ & Ashby, MF. (1997): Cellular Solids: Struc- relative density of geometrically necessary dislocations tures and Properties, 2nd ed., Cambridge University (GNDs) with decreasing indentation depth. However, in Press, Cambridge. porous materials, for foams with relative density less Oliver, WC & Pharr, GM. (1992): An improved tech- than 30%, there are a certain limit to explanation of ISE nique for determining hardness and elastic modulus using the principle due to its open-cell structure that using load and displacement sensing indentation pores in np-Au does not carry indentation force, thus experiments, J. Mater. Sci. 7, 1564-1583 GNDs does not affect the plastic deformation regions. Nix, WD & Gao, H (1998): Indentation size effect Besides, ISE mechanisms for np-Au have not been dis- in crystalline materials: A law for strain gradient cussed clearly so far. Furthermore, in case of plastic plasticity, J. Mech. Phys. Solids 46, 411-425. indentation, it has been known the hardness is nearly High temperature nanoindentation - Dynamic measure- ments for thin film analysis Dennis Bedorf, Martin Knieps, Wolfgang Stein SURFACE, Hueckelhoven, Germany Nanoindentation at non-ambient conditions has be- like creep, frequency depended modulus, or strain rate come more and more popular. Many users ask for the sensitivity. The study of these properties is depending ability to measure material properties at elevated or on temperature stability in a crucial manner. We will lowered temperatures. The materials of interest are present recent progress in the control of temperature metals, semiconductors and polymers. The investiga- stability and homogeneity of the tested volume and tion of polymers and of some metals at elevated tem- give examples in the field of polymer characterization peratures often includes time dependent properties and creep measurements. 387 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Ductility in cold-rolled ultrafine-grained (UFG) tungsten (W): Correlation between microstructure and mechanical proper- ties Simon Bonk, Jens Reiser, Jan Hoffmann, Michael Rieth Karlsruhe Institut of Technology, Institute for Applied Materials – Applied Materials Physics, Karlsruhe, Germany The progress in energy technologies, be it future pro- this purpose, three main aims are projected: (1) char- cesses like fusion or optimizing the efficiency in exist- acterize the microstructure and defect structure of ing applications by higher temperatures, demands new the as-received plates, (2) determine the mechanical materials with enhanced thermomechanical and ter- properties and access the deformation mechanisms in- mophysical properties. From a functional point of view, directly by mechanical testing as tensile- and indenta- tungsten has outstanding properties like the highest tion-SRS-tests, (3) access the deformation mechanisms melting point of all metals, a high recrystallization tem- directly by high-resolution electron microscopy. perature, good thermal conductivity, as well as high In this poster the actual results of the basis analysis of temperature strength and creep resistance. The main the microstructure and a first correlation to mechan- problem of tungsten for the application as a structural ical properties will be presented. EBSD–studies show material is its high brittle to ductile transition temper- the evolution of the microstructure with increased true ature (BDTT), resulting in brittle behavior at low tem- strain and allow determining the grain size and texture peratures and a difficult manufacturing process. Wei of the samples. A grain refinement from fine grained and Kecskes [1, 2] showed the possibility of tailoring well down to the UFG regime could be verified. Micro tungsten down to the UFG (ultrafine-grained) regime hardness measurements verify a continuous increase by severe plastic deformation (SPD). This leads to much of the hardness with decreasing grain size up to 700 higher strengths, a reduction in strain rate sensitivity HV0.1, demonstrating the positive effect of the grain (SRS), an increase in ductility and an elastic, nearly per- refinement in the UFG regime of tungsten compared fectly plastic stress-strain-behavior. Furthermore a sig- to coarse-grained tungsten which exhibits a degree of nificant toughness and a decrease of the BDTT by sev- hardness under 500 HV0.1. eral 100°C were demonstrated for thin cold-rolled foils [3, 4], validating their potential for the use in structural References applications. But despite a few interesting findings, a [1] Q. Wei, R. Valiev et al., Mechanical behavior and systematic study of the various aspects of plastic defor- dynamic failure of high-strength ultrafine grained mation of SPD processed ultrafine grained (UFG) W is tungsten under uniaxial compression, Acta Mater. still lacking [5]. (2005). To shed light on the deformation mechanisms in [2] L.J. Kecskes, Q. Wei et al., Grain size engineering of UFG-W and to access the question if the good prop- bcc refractory metals: Top-down and bottom-up— erties in tungsten foils result from the ultra-fine grain Application to tungsten, Mat. Sci. Eng. A 1-2 (2007) size or could already be found in cold-rolled foils with 33–43. coarser grains, a batch of W-sheets with different thick- [3] J. Reiser, R. Pippan et al., Tungsten (W) Laminate nesses has been produced by subsequent cold-rolling Pipes for Innovative High Temperature Energy Con- by PLANSEE, Reutte. All plates are rolled out of the version Systems, Adv. Eng. Mater. (2014). same sintered compact of commercially pure tungsten [4] A. Németh, J.Reiser, D. Armstrong, M.Rieth, The (99,97% W). This unique batch of samples allows in- nature of brittle-to-ductile transition of ultra fine vesting the mechanical properties without an influence grained tungsten (w) foil, Int. J. Refract. Met. H. 50 of the chemical composition or fabrication differences (2015) 9-15. in the production of the sintered compact. The me- [5] Q. Wei, L. J. Kecskes, Effect of low-temperature chanical properties can thereby be correlated directly rolling on the tensile behavior of commercially pure to the grain size and cold-work induced defects. For tungsten, Mat. Sci. Eng. A 1-2 (2008) 62–69. 388 Poster Topic E: Size effects and small-scale mechanical behavior of materials Fabrication of Al-Cu Composite Reinforced with BN by Pow- der Liquid-Phase Forging Cunguang Chen1, Leichen Guo2, Wenwen Wang1, Ji Luo1, Zhimeng Guo1 1Institute of Advanced Materials and Technology, University of Science and Technology Beijing, Beijing, China 2School of Engineering, Rensselaer Polytechnic Institute, Troy, USA Semi-solid powder processing (SPP) has attracted in- a good interface consisted of Al/Al2O3/BN was appar- creasing interest, which involves compaction of metal- ent in the composite. However, there are no findings lic alloy powders or element powders in temperature of AlN, AlB2 and AlB12 from the interfacial reaction ranges when both solid and liquid phases coexist (Wu between BN and Al as other research reports (Lee & & Kim 2014). Powder liquid-phase forging (PLF) be- Sim 2002; Xia & Li 2005). Compared with the basis al- longs to the category of SPP, which can be successfully loy, the composite hardness was increased nearly by applied in processing of alloy materials and composite 15%, and the composite with 2 μm aluminium powder materials. showed the better performance. These findings were Gas atomizing aluminum powder, electrolytic copper caused by the compact oxidation film naturally formed powder and hexagonal boron nitride (h-BN) powder on the surface of aluminum powder. It is noteworthy were used as raw materials. Al-5.3 wt% Cu composite that the film thickness of 2 μm aluminium powder was reinforced with 3.0 wt% h-BN with nearly full desi- larger than 35 μm aluminium powder. The former was fication was fabricated by the process of powder liq- about 20 nm, while the latter was 2 nm or so observed uid-phase forging with the load pressure 10 MPa. The by high resolution transmission electron microscopy powder morphology and comparative structural char- (HRTEM). acteristics were analyzed using X-ray diffraction, scan- ning and transmission electron microscopy, and the References composite hardness was measured by Brinell tester. Wu, Y.-F. & Kim, G.-Y. (2014): Compaction Behavior Special attention was paid to the effects of the tech- of Al6061 Powder in the Semi-solid State. Powder nique on the densification and the interface bonding of Technology, 214: 252-258; Lausanne. as-forged composites. These revealed the composite Lee, K.-B. & Sim, H.-S. (2002): Tensile Properties and densification can be promoted effectively with plenty Microstructures of Al Composite Reinforced with BN of embedded liquid phase under pressure. The com- Particles. Composites Part A: Applied Science and posites fabricated using aluminium powder with differ- Manufacturing, 33: 709-715; Oxford. ent granularity showed different grain characteristics, Xia Z. & Li Z. (2005): Structural Evolution of Al/BN and in situ recrystallization occurred inside the original Mixture during Mechanical Alloying. Journal of Al- grains with 35 μm aluminium powder. Moreover, loys and Compounds, 399: 139-143; Lausanne. Mechanical response of nanoporous gold made from Au-Ag precursor alloys with different initial microstructure Eun-Ji Gwak, Young-Cheon Kim, Ju-Young Kim School of Materials Science & Engineering, UNIST (Ulsan National Institute of Science and Technology), Korea Nanoporous metals have been widely studied for cata- atoms at the surface of alloy dissolve into nitric acid lyst, sensor, actuator and other applications due to their leaving gold adatoms, and gold adatoms agglomerate open cell porous structure with high surface-to-volume into a form of interconnecting ligament. In this process, ratio. And nanoporous gold(np-Au) has been the sub- size of ligaments and pores can be varied by controlling ject of extensive research due to their chemical in- dealloying conditions, such as concentration and tem- ertness, high electrical and thermal conductivity, and perature of nitric acid, composition of Ag-Au precursor biological compatibility. Nanoporous structure is eas- alloy and time of etching (Gwak, E.-J. 2013). The re- ily fabricated via dealloying, which use difference in sulting structure consists of open cell porous material chemical reactivity of elements in precursor alloy. For where dimension of ligament is from tens of nanome- nanoporous gold, less noble silver of gold-silver alloy ter to hundreds of nanometer. is removed chemically in nitric acid (HNO3) to make a As new materials such as nanoporous metals are de- porous structure with gold. In dealloying process, silver veloped, mechanical properties of nanoporous mate- 389 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 rials should be investigated for practical use. In bulk Ag-Au alloy is pressed until thickness decreases to materials it has been shown that, at the nanoscale less 95% to increase dislocation density without noticeable than 100 nanometer, grain size and sample size affect grain size changes. Sacrificial Ag element is selectively the overall mechanical strength (Kim, J.-Y. 2010). Simi- leached in 35% nitric acid at 80℃. Microstructures of larly, size of ligaments and pores (Biener, J. 2006) and precursor and nanoporous gold are observed by scan- relative density (Gibson, L.J. 1999) affect the strength ning electron microscope (SEM), energy-disperse X-ray of nanoporous gold. In bulk material, microstructures spectroscopy (EDAX) and electron backscattering dif- such as grain boundary or dislocation density have a fraction (EBSD). Mechanical property and deformation strong influence on mechanical property, but effects of behavior of nanoporous gold with various microstruc- grain structure and dislocation density of nanoporous tures are analyzed by nanoindentation curves. gold have not been investigated. In this research, me- chanical property and deformation behavior of nanop References orous gold with different microstructure is studied by Gwak, E.-J. et al. (2013): Microstructure evolution in nanoindentation. nanoporous gold thin films made from sputter-de- There are some researches that microstructure of pre- posited precursors, Scripa Materialia, 69, 720-723. cursor survives through dealloying process. Therefore, Kim, J.-Y., et al. (2010): Tensile and compressive be- by controlling microstructure of precursor alloy, nano- havior of tungsten, molybdenum, tantalum and porous gold with different microstructure is obtained. niobium at the nanoscale. Acta Materialia, 58, In this research, tens of nanometer grain, hundreds of 2355-2363. micrometer–sized grain, and micrometer-sized grain Biener, J., et al. (2006): Size effects on the mechanical with high dislocation density are chosen. Nanocrystal- behavior of nanoporous Au. Nano Letters, 6, 2379- line Ag-Au precursor alloy is fabricated by high ener- 2382. gy ball milling using ball mill. After heat treatment at Gibson, L.J., Ashby, M.F. (1999): Cellular Solids: 850℃ without ball milling, Ag-Au precursor has sev- Structure and Properties. Cambridge University eral hundreds micrometer-size grain. And annealed Press. Simulation of mechanical properties of nanotwin-strength- ened metals 1H. Hosseini-Toudeshky, 1M. Yadollahpour 1Department of Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran The nanotwin-strengthened metals have provided a to characterize the failure process and the numerical novel potential for optimizing the strength and duc- results are compared with nanotwin-strengthened tility of coarse grained materials. In this paper, finite copper. The results show that the material strength element simulations based on the mechanism-based and ductility strongly depend on the grain size and the strain gradient plasticity and the Johnson–Cook failure distribution of twin lamellae microstructures in these criterion has been carried out to investigate tensile be- materials. Also, the comparison between the results havior of the nanotwin-strengthened metals. Constitu- of numerical calculation and experimental data shows tive equations of the nanotwin-strengthened metals is that the proposed model adopted in the present re- employed based on a mechanism-based strain gradient search can well characterize the mechanical properties plasticity model to describe the flow stress of these ma- and size effect of nanotwin-strengthened copper. terials by incorporating the competition and transition of different deformation mechanisms as the twin spac- Keyword: nanotwin-strengthened metal; mecha- ing is reduced. Then, a finite element analysis, together nism-based strain gradient plasticity; Johnson–Cook with the Johnson–Cook failure criterion, is performed failure criterion; mechanical properties. 390 Poster Topic E: Size effects and small-scale mechanical behavior of materials Nanotubular ZnO for flexible gas sensor Na-Ri Kang, Ju-Young Kim School of Materials Science & Engineering, UNIST (Ulsan National Institute of Science and Technology), Korea ZnO has been focused on hydrogen sensing ma- studies, tensile properties of ZnO thin film have not terial because of its thermal stability and high been reported, so we tried that. After ZnO was de- machenical strength and mobility. But it has the posited on gold thin film by equal ALD condition, dog- weakness that it is very brittle. And nowadays, flex- bone shaped pattern prepared by photolithography. ible electronics technologies are beeing driven by Dog-bone shaped ZnO thin film were obtained by re- trend such as low complexity and high reliability. active-ion etching becuase dog-bone shaped positive A high strength-to-weight ratio makes interconnected photoresist protected ZnO during etching other region. tubular networks an creative design strategy for re- Tensile testing of ZnO thin film and nanotubular ZnO ducing the linear decrease in strength and stiffness of was performed by using the nano-tensile tester under low-density materials with increasing porosity. So we conditions of a speed of 2μm/s at a distance of 2mm. synthesized ultralow-density nanotubular structured We discuss flexibility of the nanotubular ZnO based on ZnO with high surface area to volume ratio for flexi- its nanotubular structure or shell thickness. We also bile hydrogen gas sensor application using the sacri- measured hydrogen gas sensing sensitivity, defined as ficial templatet, nanoporous gold. We measured its a raio of change in conductance upon exposure to H2 mechanical properties by tensile test and hydrogen gas gas to that in vacuum, of the ZnO thin film and nano- sensing sensitivity. Dog-bone shaped nanoporous gold tubular ZnO. We discuss hydrogen sensor efficiency of with pore size 1 ㎛, gauge length 2 mm was prepared the nanotubular ZnO based on its high volume-to-su- by free corrosion dealloying from gold-silver mother frace area and application of flexible hydrogen gas sen- alloy. For nanotubular structured ZnO, 50, 100, 150 sor. nm-thick ZnO layer was deposited on nanoporous gold by atomic layered deposition (ALD). After nanoporous References gold was selectively etched by gold etchant TFA, nano- Hsial, C. (2014) : A Rapid process for Fabricating Gas tubular structured ZnO which have shell thickness of Sensors., Sensors 12219-12232; doi: 10.3390/ 50, 100, 150 nm were obtained. We synthesized ZnO s140712219 thin film with 50, 100, 150 nm-thick to compare me- Biener, M. (2014) : Ultra-strong and Low-Density Na- chanical properties and hydrogen gas sensing sensitiv- notubular Bulk Materials with Tunable Feature Siz- ity with nanotubular structured ZnO. And in privious es., Adv. Mater., 26: 4808–4813 Improved elasticity of bilayer graphene cantilevers with in- terlayer shear and in-plane extension effects Abed Moheb Shah Din, Amin Farrokhabadi Aerospace Department, Engineering Faculty, Semnan University, Iran Graphene is measured to be the strongest and a one Walls bond when the external force exceeds the forces atom thick material whose usage has been widely re- between graphene layers. Since the classical Euler-Ber- ported in various applications especially in electronic noulli beam theory cannot simulate the interlayer devices. Due to its remarkable electrical, thermal and shear effect, multi-beam shear model has been con- stable mechanical properties, graphene has become an ducted in recent years to illustrate the governing equa- interesting field of research in scientific communities. tion of graphene multilayer beam. As a result of the outstanding properties of graphene, It is worthy to note that the multi-beam shear model is it appears to be one of the best candidates in designing a reduced form of the model proposed and applied by reinforced nanoelectromechanical systems (NEMS) de- Newmark in (1952) for composite beams. Newmark’s vices such as nano-actuators, resonators and the other theory includes interlayer shear which involves inter- possible nano-structures with high stiffness. layer shear modulus and interlayer stretching which Graphene layers have been observed to slide over each has been neglected in the past few studies. other within multilayered structures like graphene na- In this letter, we are proposing an improved governing noribbon (GNR) due to the weak interlayer van der elasticity of bilayer graphene cantilever beam sub- 391 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 jected to a concentrated load at the beam tip in order References to investigate the effect of in-plane extension on the Rokni, H & Wei, Lu. (2013): Effect of graphene layers graphene layered beams. The interlayer shear effect on static pull in behaviour of bilayer graphene/sub- and in-plane extension are simulated through mini- strate electrostatic microactuator. Journal of Micro- mum energy principle moreover the governing equa- electromechanical Systems, Vol.22, No. 3. tion and boundary conditions are given consequently. Liu, D.Y & Chen, W.Q & Zhang, Ch. (2013): Improved Results indicate that the extension in layers occurs due beam theory for multilayer graphene nanoribbons to the interlayer shear modulus as in zero interlayer with interlayer shear effect. Physics Letters A 377, shear modulus, i.e. no bond between layers, the ef- 1297-1300. fect of extension is practically nil. On the other hand, Alfredsson, K.S & Bogetti, T.A & Carlsson, L.A & Gil- considering extension in layers, the structure behaves lespie, J.W & Yiourans, A. (2008): Flexure of beam softer compared with the case in which the interlay- with an interlayer– Symetric beam with orthotropic er extension is neglected. In order to give a proper in- adherends. Journal of Mechanics of Materials and sight, the behaviour of bilayer beam is discussed and Structures. Vol. 3, No. 1. shown in absence and presence of interlayer shear and extension. Fracture of brittle spheres in compression: testing micro- scopic fused quartz Vaclav Pejchal, Goran Žagar, Denis Lang, Marta Fornabaio, Andreas Mortensen Laboratory of Mechanical Metallurgy, Institute of Materials, EPFL, Switzerland The crushing of particles between two parallel plat- where the particle contacts the hard diamond platens. ens is widely used as particle fracture has relevance In this study we explore the use of softer elasto-plastic in many branches of engineering (powder metallurgy, platens, which reduce the stress concentration at the food or pharmaceutical industries and of course mate- contact point with hard, brittle particles. We develop rials science). Recent years have seen increased atten- the method on a laboratory-built instrumented crush- tion to micro and nano-mechanical testing, a combined ing apparatus, which we use here to crush microscopic result of interest in expanding the field of application fused quartz particles. The use of soft platens leads to of the method, and progress in testing methodologies the development of a higher contact area over which and tooling at the microscale. the load is applied on the particle. The particle partially Although the implementation of such test is relative- sinks into the platen leaving an indentation, the size of ly easy, at the microscopic scale it is often realized by which is controlled chiefly by the elasto-plastic proper- crushing a particle between two hard platens, typically ties of the platens. The higher area over which the load of diamond. This often leads to particle failure by the is applied leads to lower local stresses at the contact propagation of defects initiated at the particle/platen compared to the tensile stresses that develop (i) in the contact due to the very high local stresses that are center of the sphere and/or (ii) at the equatorial belt of reached at this point. Resulting test data therefore do the sphere surface. In combination with extensive FEM not sample the weakest existing flaws within the parti- analysis we explore how this modification of the parti- cle or along its surface; rather, the failure is induced by cle crushing test can be used as a means of measuring microcracks that develop at the contact during the test, the strength of particles. 392 Poster Topic E: Size effects and small-scale mechanical behavior of materials How to optimize the fatigue properties of bimodal micro- structures of nanocrystalline (nc) and ultrafine grained (ufg) Nickel? Dominic Rathmann, Michael Marx, Christian Motz Saarland University, Chair of Materials Science and Methods, Saarbrücken, Germany Nc-materials show very high strength compared to an important role; however the abnormal behavior their coarse grained counterparts. On the contrary, has not been investigated satisfactorily so far. Therefor they provide only low ductility and an insufficient re- atom probe tomography is used to study the effect of sistance against fatigue crack growth. An approach to segregation. fix this deficit for a single-phase material is to modify To measure the effect of the microstructure´s modifi- the nc-microstructure to a bimodal “composite” con- cation concerning the fatigue strength, Wöhler-tests of sisting of nc- and ufg-grains which has much better monomodal nc- and ufg-samples as well as bimodal nc/ fatigue properties than the respective monomodal ufg-samples were performed and evaluated for the LCF microstructures. The bigger ufg-grains enable plastic and HCF region. Furthermore crack propagation mech- deformation and improve the crack resistance while anisms have been investigated by in-situ tests in SEM. the nc grains preserve the high toughness. The monomodal microstructures work as reference. Starting from pulsed electrodeposited nc-Nickel, bi- Goal of the present work is to identify and produce an modal microstructures can be developed by adding optimal microstructure concerning the fatigue prop- special additives to the electrolyte in combination with erties of nc materials without losing the increased a following heat-treatment of the material. The un- strength and toughness. Therefor the ratio and vol- derlying effect is the abnormal grain growth of single ume fraction of nc- and ufg-grains will be varied by the grains. Thereby, segregation at grain boundaries plays amount of additives and different heat treatments. Surface oxidation of metallic glass surfaces and its effect on na- notribology K. Rittgen1,2, A. Caron1, R. Bennewitz1,2 1INM Leibniz-Institute for New Materials, Saarbrücken, Germany 2Department of Experimental Physics, University of Saarbrücken, Germany Owing to their high strength and hardness metallic References glasses have been recognized as potential materials A. Caron et al. 2011: Structure and nano-mechanical with enhanced wear resistance for tribological applica- characteristics of surface oxide layers on a metallic tions (A.L. Greer et al. 2002). While metallic glasses are glass; 2011 Nanotechnology 22 095704 (2011); prone to oxidation, the formation of surface oxide and A Caron, C L Qin, L Gu, S Gonzales, A Shluger, H-J its impact on tribological properties has been scarcely Fecht, DV Louzguine-Luzgin, A Inoue investigated (A. Caron et al. 2011, A. Caron et al. 2011). A. Caron et al. 2011: Effect of surface oxidation on the In this work we use a correlative approach to deter- nm-scale wear behavior of a metallic glass; Journal mine the influence of surface structure and chemistry of applied physics 109, 083515 (2011); A. Caron, P. on the friction and wear of metallic glass surfaces. Sur- Sharma, A. Shluger, H-J Fecht, DV Louzguine-Luzgin, face structural properties are investigated by nc-AFM A Inoue in ultra-high vacuum after Ar-sputtering and controlled A.L. Greer et al. 2002: A.L. Greer, K.L. Rutherford, and oxidation treatments. Surface oxides are further char- I.M. Hutchings, Inter. Mater. Rev. 47, (2002) 87 acterized by TEM and XPS. The tribological behavior of metallic glass surfaces with and without oxide layer is determined by AFM- and nano-scratching. 393 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Investigation of mechanical anisotropy in Mg using Berkovich indentation Julian E. C. Sabisch1,2, Erica T. Lilleodden1,3 1Institute of Materials Research, Materials Mechanics, Helmholtz-Zentrum Geesthacht, Germany 2University of California, Berkeley. Department of Materials Science and Engineering, USA 3Institute of Advanced Ceramics, Hamburg University of Technology, Hamburg, Germany Bekovich indentation has been shown to be an impor- SEM indent images were further used to create a set of tant method for determining mechanical properties on ratios between the actual imaged indent area and the small length scales. (Oliver, W.C. & Pharr, G.M 2004) ideal area from a symetric tip. Ratios were differentiat- While the imposed stress state from axisymmetric in- ed based on orientation then averaged with grain (i) dentation leads to largely isotropic measurements, the showing a ratio above one and grains (ii) and (iii) having use of non-axi-symmetric indenters offers possibilities ratios less than one. A ratio greater than one would cor- to investigate anisotropy in mechanical behavior, such respond to pile up while a ration less than one would as the elastic modulus and hardness. correspond to sink in. The ratios were used to correct Here, we investigate how the relationship between the the values of modulus. Interestingly, this correction in- crystallographic c-axis direction and the Berkovich tip creased the variation between the orientations, with relate to the modulus and hardness in a Mg-4Gd single the highest average value of 53.0 GPa for the grain (ii) crystalline volumes. orientation, and the lowest average value of 47.2 GPa A sample of cast Mg-4Gd was selected for the experi- for the grain (i) orientaiton. These results show that the ments due to its large grains and resistence to the for- use of Berkovich indnetation can be used to investigate mation of a surface oxide. Electron backscatter diffrac- the anisotropic plastic response in hcp systems, such tion was used to find suitable grains for indentation. as technological Mg- and Ti-based alloys – materials of Grains with the three distinct orientations were cho- critical interest for lightweight structural applications sen: (i) with the c-axis normal to the surface, (ii) with – where bulk single crystals are not readily attainable. the c-axis at an ~45° angle to the surface, and (iii) with the c-axis in-plane. All indentations were carried out References to a nominal maximum depth of 3000nm, with a 75μm Oliver, W.C. & Pharr, G.M (2004): Measurement of indent spacing. The same sample was used without re- hardness and elastic modulus by instrumented mounting in order to remove any load frame stiffness indentation: Advances in understanding and refine- changes and to maintain the initial surface to indent ments to methodology; J. Mater. Res., Vol. 19, No. 1, allignment for all tests. Initial testing of all grain orien- Jan 2004. tations showed a slight variance in both modulus and Vlassak, J.J., & Nix, W.D. (1994): Measuring the elastic hardness. SEM imaging was used to investigate the properties of anisotropic materials by means of residual indentation. Again, dependance on orienta- indentation experiments; J. Mater. Res., Vol. 27, No. tion was observed. Highly symmetric indents with ap- 1, Jan 14, 2012. preciable pileup in the c-axis normal orientation were Zambaldi, C., et al. (2012): Orientation informed na- observed. Conversly, orientations with the c-axis not noindentation of α-titanium: Indentation pileup in aligned with the loading direction displayed considera- hexagonal metals deforming by prismatic slip; J. ble sink-in and an elongation of the indent impression Mater. Res., Vol. 27, No. 1, Jan 14, 2012. along the direction coincident with the projected c-ax- is. 394 Poster Topic E: Size effects and small-scale mechanical behavior of materials Size- and phase-dependent mechanical properties of ultra- thin silicon and Ge2Sb2Te5 films Franziska Schlich, Ralph Spolenak ETH Zürich, Laboratory for Nanometallurgy, Zürich, Switzerland Ultrathin semiconductors or phase-change materi- Moreover, the results follow the trend of increasing als (5-30 nm) on metals constitute color filters, which onset strain of fragmentation with decreasing film selectively absorb wavelength ranges of the incident thickness. light (Kats et al., 2012). Recently, it was demonstrated Besides optical data storage and display applications that these coatings are attractive for tunable color de- these results are of great interest for MEMS applica- vices (Hosseini et al., 2014; Schlich et al., 2014). Color tions and ultrathin solar cells. change of ultrathin Si and Ge2Sb2Te5 was induced by reversible switching between the amorphous and crys- References talline phase. These structures hold significant promise Kats et al. (2012): Nanometre optical coatings based for optical data storage and for flexible display applica- on strong interference effects in highly absorb- tions. During operation thermal stress caused by tem- ing media- In Nature Materials 12: Kats, M.A. perature gradients are introduced and could lead to Blanchard, R., Genevet, P., Capasso, F., 12, (20-24). failure of the material. The mechanical properties of Si Hosseini et al., (2014): An optoelectronic framework (Oh et al., 2005) and Ge2Sb2Te5 (Choi et al., 2010) have enabled by low-dimensional phase-change films- In been investigated before. However, crack formation in Nature, Hosseini, P., Wright, C.D., Bhaskaran, H., 511 ultrathin semiconductors and phase-change materials (206-211). have yet to be reported. Schlich et al., (2014): submitted in ACS Photonics, Here, the mechanical properties of these ultrathin Schlich, F.F., Zalden, P.; Lindenberg, A.M., Spolenak, films are determined by uniaxial tensile tests in de- R. pendence of the film thickness. Si and Ge2Sb2Te5 films Oh et al., (2005): Comparison of the Young’s modulus in the thickness range between 10 nm and 50 nm are of polysilicon film by tensile testing and nanoinden- sputter deposited on polymeric substrates. The onset tation- In Sensors and Actuators A: Physical, Oh, strain of fragmentation is measured and the crack for- C.-S., Lee, H.-J., Ko, S.-G., Kim, S.-W., Ahn, H.-G., 117, mation is investigated for amorphous and crystalline (151-158). films. Different methods like resistance measurements, Choi et al. (2010): Elastic Modulus of Amorphous optical microscopy, Raman spectroscopy and scanning Ge2Sb2Te5 Thin Film Measured by uniaxial Mi- electron microscopy are applied to observe the crack crotensile Test- In Electronic Materials Letters, Choi, development in the films. Generally, cracks occur later Y., Lee, Y.-K., 6, (23-26). for amorphous films in comparison to crystalline films. Compression-shear behavior of a strongly textured Magnesi- um alloy AZ31 under different strain rates Sebastian Seipp1, Shibayan Roy², Benjamin Zillmann1, Martin F.-X. Wagner1 1 TU Chemnitz, Institute of Materials Science and Engineering, Chemnitz, Germany 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, USA Texture plays a key role in determining anisotropy and sion-shear specimens are taken from the material ori- mechanical properties of magnesium alloys. Here, we ented such that the preferred shear direction is parallel study the deformation behavior of a strongly textured to the last shear plane induced by the final ECAP pass. AZ31 magnesium alloy processed by Equal-Channel The specimens are tested at three different strain rates Angular Pressing (ECAP) under compression-shear (10-3, 100, 102 s-1), ranging from quasi-static to dynamic, loading. For compression-shear testing, we use a spe- and strain fields are evaluated with a digital image cor- cial sample geometry (tilted cylinder geometry) that relation (DIC) system. In case of the lower strain rates, leads to super-imposed shear stresses (and a preferred texture dominates the material behavior in terms of shearing-direction) within the sample under nominal- plastic deformation, crack propagation and fracture ly uniaxial compressive loading. After ECAP, compres- behavior even when the super-imposed shear stresses 395 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 are supposed to promote deformation along different ly stronger impact of thermo-mechanical conditions directions. At high strain rates, however, the material during dynamic testing. Our results provide a detailed is observed to fail in the direction of the highest shear picture of the interaction between microstructure and stresses, and this behavior can be rationalized by con- texture, complex loading conditions and fracture be- sidering (quasi) adiabatic processes and the relative- havior of AZ31. Roughness behaviour of nanomaterials Sayah Tahar, Bouti Samir USTHB, Faculty of Mechanical Engineering, Algiers, Algeria We propose an experimental study of the surface to The identification of the real contact area was carried dry and analysis of the evolution parameters rough- out using a special algorithm based on single profile ness. The simplified model was proposed to predict analysis. The single, randomly selected profiles were the metrological parameters in the contact area of the extracted from the measured topography of the de- deformed surface. The model is based on the analysis formed surface. It should be noted that the profiles ob- of the topography 3D of the deformed surface. tained in this way have a common reference level. The Study aims to characterize the topography of sintered selected profiles also have the same direction, which, materials obtained by wear tests. Therefore it is inter- in the case of anisotropic surfaces (turning, grinding) esting initially in the evolution of wear for the loads should be perpendicular to the direction of the move- applied and to characterize the different roughness ment of the machining tool. The proposed model was emerging from 3D AFM observations. applied to analyze a wear of four kinds of rough surfac- Experimental and theoretical research on the topogra- es. The predicted values were compared with experi- phy changes during dry contact deformation was car- mental results. ried out in [1], [2], [3] and [4], providing results that The wear and surface roughness based on the param- demonstrate the persistent nature of roughness asper- eters of dry friction tests were measured. This study ities even under high loading when bulk plastic defor- suggested the optimal parameters of chemical compo- mation appears. Most theoretical investigations of the sition, and analysis of the effects alloying elements on problem have been based on a simplified model ne- surface roughness and wear in the process dry friction glecting the statistical distribution of asperities on the tests. real surface, [5]. In [6] used test and 3D measurement of surface topography in order to investigate its fric- References tional behaviour. The mechanism of contact of a rigid R. G. Bayer, P. A. Engel, J. L. Sirico, (1972) Impact wear plane with a rough surface in the presence of a lubri- testing machine, Wear, 19, pp. 343–354 cant is different than in the case of dry contact. S. L. Rice, S. F. Wayne, H. Nowotny, (1980) Material The topography of the samples was measured both in transport phenomena in the impact wear of titani- initial undeformed and in the deformed state after re- um alloys, Wear, 65, pp. 215–226 moval of the load. In these states, however, a change of S. L. Rice, S. F. Wayne, H. Nowotny, (1981)Character- the shape of the samples when compared to the initial istics of metallic subsurface zones in sliding and state was observed. Thus, prior to the determination impact wear, Wear, 74, pp. 131–142 of roughness parameters of the deformed surfaces, A. Bartoszewicz, J. Radziejewska and G. Starzyński, their curvature was removed using a filtration proce- (2004), 3D roughness analysis of deformation of dure. surface at contact loading, Adv Manuf Sci Technol The essential differences in surface topography of sam- 28 (4) pp. 17–30 ples loaded in dry condition are confirmed in the anal- Hibi, Y., Miyake, K., Murakami, T., Sasaki, S. (2006) Tri- ysis of roughness parameter evolution. The following bological behavior of SiC-reinforced Ti3SiC2-based 3D parameters were considered. In the unloaded state, composites under dry condition and under lubricat- flattened asperities can be observed on the deformed ed condition with water and ethanol, J. Am. Ceram. surface Fig 1.a. The real contact area corresponding to Soc, 89(9), pp. 2983–2985 the maximal load attained in the surface compression Zhang J J, Zhu J H. (2009) Surface structure evolution experiment can be identified from measurement of the and abnormal wear behavior of the TiNiNb alloy deformed roughness after unloading. under impact load, Metall MaterTrans A , 40, pp. 1126–113 396 Poster Topic E: Size effects and small-scale mechanical behavior of materials Electronic properties and mechanical stability of ZnO in the bulk and nanowire structures under large uniaxial stresses Lucy A. Valdez, Ricardo A.Casali Facultad de Ciencias Exactas y Naturales y Agrimensura, Universidad Nacional del Nordeste, Corrientes, Argentina ZnO is a semiconductor with a wide range of techno- composed by cells of 48 atoms with periodicity 1c and logical applications due to its physical advantages: di- 2c along [0001] direction and 108 atoms, with peri- rect wide band gap, large excitation binding energy, odicity 1c. We have chosen the hexagonal shape be- high thermal conductivity and piezoelectricity.[1] In cause it is the most stable in growth ZnO nanowires. addition, ZnO is very important in high-pressure phys- [5] Its total energies, solid pressure, stress tensor and ics where it has been probed experimentally that ZnO residual forces was compared and we choose the most transforms from hexagonal wurtzite (B4) to rocksalt stable cell for our studies. Then, a strain along the c (B1) under hydrostatic pressures.[1] Some of the ZnO vector was applied to determine the Young modulus properties are improved in the nanosize scale, special- and the break tensile of the nanowire into the cell. The ly its piezoelectric and semiconducting properties. For obtained values are in agreement with other DFT cal- this reason, we have been studying ZnO(B4) nanowire culation.[5,6] and bulk material in order to compare its properties By the application of uniaxial strains until 10 GPa, we due to confinement. have calculated the NW Poisson coefficient, variation In the present work, we have first analyzed ZnO using of lattice vectors with pressure and changes in a hexag- the SIESTA [2] and ABINIT codes [3] in the bulk materi- onal area bounded by Zn atoms. The more important al. Our calculations with SIESTA were performed using changes are seen around 6 GPa and 7 GPa, which cor- the generalized gradient approximation (GGA) and the respond to nanowires with 48 and 108 atoms, where local density approximation (LDA). layers of atoms move away from each other and we Then ZnO was subjected to hydrostatic pressures un- could device a possible phase transition under uniax- til 10 GPa. Nearby to 4 GPa, the system has presented ial stress. In the NW band structure we found a band an anomalous behavior. The same situation appeared gap (1.5 eV) larger than the calculated in bulk material when we employed the ABINIT code and it allowed us (0.9 eV), which is associated to quantum confinement to associate such behavior to a possible phase transi- effects. tion. The lattice parameters, equilibrium volumes, bulk modulus and its pressure derivate were close to exper- References imental results and other theoretical assessments. [1] [1] Zinc oxide: Fundamentals, Materials and Device The phonon modes, which were calculated with SIESTA Technology. H.Morkoç, Ü.Özgür. 2009. WILEY and ABINIT at the center of the Brillouin zone, are in ex- [2] User’s Guide SIESTA 3.1. Emilio Artacho et al. cellent agreement with other theoretical calculations (2011) and experiment results [1], specially the when using [3] X. Gonze et al., Comput. Mater. Sci. 25, 478 the LDA-GGA hybrid functional. On the other hand, our (2002); see website: http://www.abinit.org calculations with ABINIT code provide a lattice param- [4] P. Gopal and A. Spaldin. Polarization, piezoelectric eters, bulk modulus, elastic and piezoelectric constants constants and elastic constants of ZnO, MgO and close to experiments.[1,4] CdO. 2005. arXiv:cond-mat/0507217 In the case of ZnO nanowires using the SIESTA code, [5] S. Haffad et al. Energy Procedia 10 128 (2001) we have considered non-interacting hexagonal NWs [6] R. Agrawal et al. Nano Lett. 2010, 10, 3432-3438. 397 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 First-principles study on ferroelectricity and its coupling behavior with mechanical deformation of ultrathin PbTiO3 nanotube Xiaoyuan Wang1, Takahiro Shimada2, Takayuki Kitamura2 1Institute of Systems Engineering, China Academy of Engineering Physics, Mianyang, China 2Department of Mechanical Engineering and Science, Kyoto University, Japan In this study, the ferroelectric (FE) properties and its and axial strain has also been studied. The axial polar- coupling behavior with mechanical strain of ultrathin ization of nanotube is enhanced by the tensile strain. PbTiO3 nanotubes are investigated by first-principles On the other hand, with the increase of compressive calculations. Different from the thin films, the sponta- strain, the axial polarization becomes weak and disap- neous polarization still exists in the nanotube despite pears, and the nanotube structure becomes paraelec- their sidewalls being thinner than the critical thickness tric state. With the further increase of compressive at which the thin films lose ferroelectricity (Fong et al strain, a vortex type of polarization emerges along the 2004), which indicates the absence of an intrinsic crit- circumferential direction, and the nanotube structure ical size of ferroelectricity in the nanotube structure. becomes ferroelectric state again. These rich phase The total energy of nanotube is lower than that of the transitions in the nanotube structure are induced by thin film. This means that the nanotube structure is en- the change of covalent Pb-O bond due to the applied ergetically more stable than the thin film. Moreover, strain. Finally, the mechanical strength of PbTiO3 nano- the ground state of the nanotube is not purely FE since tube is evaluated, and the critical stresses under the it primary involves antiferrodistortive (AFD) rotation tension and compression states are obtained. of oxygen atoms due to compression in the inner tube wall. The emergence of the AFD displacement plays a Reference central role in stabilizing both the nanotubular struc- Fong, D. D., et al. (2004): Ferroelectricity in ultrathin ture and FE distortions due to direct AFD-FE coupling. perovskite films. Science, 304, 1650-1653. In addition, the coupling behavior of ferroelectricity Thickness-dependent tensile properties of PEDOT:PSS O Bae Woo, Ju-Young Kim School of Materials Science & Engineering, UNIST (Ulsan National Institute of Science and Technology), Korea Future electronic device will progress being trans- spin coated and annealed at 115 °C. Air dried sam- parent and flexible to apply human body. According- ples were pressed with die-cutting press to dog-bone ly researchs about wearable, stretchable devices are shape for tensile testing. Spin coated samples were studying actively. This leads increasing interest about fabricated to dog-bone shape using ion milling sys- PEDOT:PSS. PEDOT:PSS have high conductivity, high tem. Samples aligned with polypropylene jigs. PMMA transmittancy in visible light range among conducting scrifice layer was etched in acetone. Thickness of ten- polymers. So PEDOT:PSS has been researched various sile samples was 6 μm, 600nm, 60nm each. Different area like transparent electrode, solar cell, OLED fields. stress-strain curve was obtained by tensile tests de- Especially research about flexible transparent elec- pending on film thickness. We discuss about tensile trode using PEDOT:PSS is promising field. But to use properties depending on thickness of PEDOT:PSS. PEDOT:PSS to flexible transparent electrode, reliability test comes to the fore as using PEDOT:PSS on flexible References substrates. So in this study, tensile test was conducting Udo L. (2009): Mechanical characterization of PE- for reliablity estimation of PEDOT:PSS. We measured DOT:PSS thin films, Synthetic Metals 159 473-479 tensile properties of PEDOT:PSS and compared data Udo L. (2009): Microscopical investigations of PE- depending on thickness of PEDOT:PSS. DOT:PSS thin films, Adv. Funct. Mater. 19, 1215- Copper thin film was deposited polypropylene sub- 1220 strate for spin coating. PMMA funcion as scrifice layer Y. Y. Lee. (2013): Stretching-induced growth of PE- was spin coated on copper thin film. PEDOT:PSS was DOT-rich cores: A new mechanism for strain-de- prepared by two methods. Mico-scale samples were pendent resistivity change in PEDOT:PSS, Adv. Funct. air dried at ambient conditions more than 12 hours Mater. 23, 4020-2027 after spread on substrate. Nano-scale samples were 398 Poster Topic F: Advanced steels and steel composite materials Poster Topic F: Advanced steels and steel composite materials 399 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Effect of filler metal on micro-structural, mechanical and cor- rosion behavior of austenitic stainless steel weldment 316L A. Sriba1,2, K. M. Rehouma1, S.E. Amara2, N. Madaoui3 1Welding And N.D.T. Research Centre, Algiers, Algeria 2Laboratoire D’electrochimie-Corrosion Métallurgie et Chimie Minérale, Faculté De Chimie, Université Des Usthb, Alger, Algeria 3Division Milieux Ionisés, Centre de Développement des Technologies Avancées, Alger, Algeria Austenitic stainless steels in this case 316L grade are Rusitzka, E. & Jubitz, K.-B. (1968): Trias. – In: Grundriß widely used in fields and varied industrial sectors. They der Geologie der DDR, Bd. 1: 268-89; Berlin. are generally considered wieldable if proper precau- Wolburg, J. (1969): Die epirogenetischen Phasen der tions are followed, however, they present a number of Muschelkalk und KeuperEntwicklung Nordwest- problems during and after welding: hot cracking dur- Deutschlands, mit einem Rückblick auf den Bunts- ing welding, intergranular corrosion and precipitation andstein. – Geotekt. Forsch., 32: 165; Stuttgart. of embrittling phases during prolonged maintaining in P. Lacombe, G. Beranger. « Structures et diagrammes the temperature range from 400°C to 900°C [1]. The d’équilibre des diverses nuances des aciers inoxy- remaining deposit (called seam) in these alloys has dables. Conséquences sur les traitements thermi- austeno-ferritic structure. The essential factors gover- ques», édition de physique, les Ulis, 1990. ning the metallurgical embrittlement of these deposits J.A. Brooks, A.W. Thompson « Microstructural devel- are the ferrite[2,3,4] content and the carbon content opment and solidification cracking susceptibility of of the deposited metal. The ferrite within the molten austenitic stainless steel welds». International Ma- zone plays an important role in the embrittlement of terials Reviews. 1991, Vol.36, n°1, pp.16-44. the welded alloys, its content depends mainly on the Rajasekhar K., Harendranath C. S., Raman R., Kulkarni nature of the filler metal. For this reason, the choice of S. D. « Microstructural evolution during solidifica- filler metals is an important element in the manufac- tion of austenitic stainless steel weld metals: A color ture of articles of austenitic stainless steels and ensure metallographic and electron microprobe analysis good reliability for these welds service [5].The study re- study ». Materials characterization. 1997, Vol.38 (2), ported in this paper brings out and shows the influence p. 53-65. of the chemical composition of the filler metal (ER316L Elmer J.W., Allen S.M., Eagar T.W. « Microstructural and ER308L) on the microstructure resulting after wel- Development during Solidification of Stainless Steel ding by TIG process, mechanical and corrosion beha- Alloys ». Metallurgical and Transactions A. 1989, vior of austenitic stainless steel weldment 316L.The Vol.20A, p. 2117-2131. mechanical tests are: micro-hardness and charpy im- Rehouma K., Shabadi R.S, Taillard R., Bouabdallah M., pact strength, corrosion tests is carried out in sodium Imad A. « Effect of ageing at 700°C on Ferrite Trans- chloride 3.5%. formation in a 316L/308L weldments ». Materials and Manufacturing Processes. 2012, Vol.27, Issue References 12, p.1370-1375. Allegro, M. (2006): What does it mean? – In: Turm, P., Bauer, B. & Läufer, R. (eds.): Guess what. Springer, 16-44; Hintertux. 400 Poster Topic G: Fracture mechanics Poster Topic G: Fracture mechanics 401 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Estimation of Fracture Toughness of Metallic Materials Using Instrumented Indentation Test Jun-Yeong Kim1, Woojoo Kim1, Seung-Hun Choi1, Dongil Kwon1 1Department of Materials Science & Engineering, Seoul National University, Seoul is no crack event during indentation for deformable Fracture toughness is one of the most important ma- terial properties required for Fitness For Service (FFS). metallic materials. We develop a simple and realistic In practice, however, it is usually unavailable for com- approach based on fracture mechanics and contact ponents of structures in the field since its testing can mechanics to estimate fracture toughness of metallic be difficult because of the specific specimen geometry materials. Models are developed for brittle and ductile and size requirement, the complex procedure, and the fracture. Different criteria are applied to each model to destructiveness of the method. The instrumented in- determine the critical fracture point during indentation dentation test (IIT) has been proposed as a unique solu- in terms of critical fracture stress/strain. In this study, tion to overcome these drawbacks and has been devel- fracture toughness was estimated for various metallic oped for nondestructive testing of in-field structures. materials from each model and compared with that Previous investigations, however, have encountered a measured from standard fracture-toughness test. In major problem: how to determine the critical fracture addition, we extend our models to low temperature point corresponding to crack propagation, since there tests as well. The experimental study of stress-strain states in stress con- centrators with the use of the method of digital image corre- lation Elena M. Spaskova, Evgeniy V. Lomakin Perm National Research Polytechnic University, Perm, Russia One of the important tasks in the field of solid mechan- and Instron 5989, together with the use of digital opti- ics is to study the effect of different types of stress con- cal system Vic-3D. centrators on the behavior of structural elements. As a result of the plates tensile test, transverse, lon- The aim of the work is an experimental study of the gitudinal, shear deformations, as well as the intensity stress-strain states in hubs using the method of digital deformation fields were constructed. image correlation. The use of video system made it possible to detect not In this work we consider the use of three-dimensional only changes in strain, but also to assess the impact digital optical system, Vic-3D, the mathematical appa- of stress concentrators that implement complex stress- ratus of which is based on the method of digital image strain state of the material. correlation. The system allowed to record the evolution of the The video system is designed for the analysis of dis- fields of displacements and strains to evaluate the na- placement fields and strain on the sample surface. ture of heterogeneity of fields to keep track of the ma- This article describes the technique of the experiment terial deformation processes occurring on the surface with the use of a digital optical system, its structure of the sample. The add-on software video „virtual ex- and working principle. tensometer“ was used in determining the mechanical The mathematical foundations of the computing de- properties of the material. vice system were formulated, and uniaxial compres- The high efficiency of the method of correlation of dig- sion „Brazilian test“ were done in order to develop the ital images in the study the behavior of the material in methodology of the experiment using a digital optical the event of non-uniform strain fields was shown. system. This work was carried out in the PNRPU with support The results of the uniaxial tensile tests on plates made of the Government of Russian Federation (the de- of plexiglass with concentrators of different geome- cree No. 220 on April 9, 2010) under the Contract No. tries, as well as the results of tests on a uniaxial tensile 14.B25.310006, on June 24, 2013, and Russian Fund carbon plate with a circular hole using a digital optical for Basic Research (grant № 13-08-00304, № 14-08- system, were presented. Mechanical uniaxial tensile 31387). test were performed on the test system Instron 5882 402 Poster Topic G: Fracture mechanics References al using correlation techniques digital images. PNR- Sutton M.A., Orteu J.-J., Schreier.H. (2009): Image Cor- PU Mechanics Bulletin, no. 2, pp. 186-198. relation for Shape, Motion and Deformation Measu- Tretyakova T.V., Wildemann V.E. (2014): Study of spa- rements. – University of South Carolina, Columbia, tial-time inhomogeneity of serrated plastic flow SC, USA – 364 p. Al-Mg alloy: using DICtechnique. Fracture and Struc- Tretyakova T.V., Spaskova E.M. (2013): Experimental tural Integrity, no. 27, pp. 83-97. study of limit stress-strain state quasi-brittle materi- Methods of Stochastic Mechanics for Characterisation of Microstructural Failure in Heterogeneous Materials Mikhail Tashkinov, Natalia Mikhailova Perm National Research Polytechnic University, Russia The problem of determination of mechanical and obtained by connecting the microstructural correlation physical properties of heterogeneous materials is high- functions with the SBVP solution (Tashkinov 2014). The ly topical. Replacing experimental testing with mul- material properties were defined as the constants in ti-scale simulations, when material’s properties are the integral-differential equations, while loading on obtained by modelling at the smaller scales, can save the volume’s boundaries was set as the boundary con- considerable efforts. One of the major barriers for ap- ditions of SBVP. plications of multi-scale methods is complexity of a The case studies of representative volumes of fibre-re- micro-scale structure of composites. Computational inforced composites as well as of multicomponent and experimental research has proved that random- composites with randomly distributed spherical and el- ness of the microstructural geometrical and physical lipsoidal inclusions were investigated. The micro-scale parameters plays an important role in behaviour of geometry of the samples was obtained both with mod- multicomponent materials (e.g. Kwon 2008, Rasool elling and experimental analysis. The numerical results 2012). Thus, the precision of their behaviour modelling were calculated for high order statistical moments and depends on ability to consider the peculiarities of the function and were used for characterisation for failure non-periodic heterogeneous microstructure. This work prediction in micro-scale constituents of the materials. offers a model, which combine several approaches of The work was carried out at the Perm National Re- stochastic mechanics to create a tool that can assess search Polytechnic University with support of the Gov- deformation and fracture processes in heterogeneous ernment of Russian Federation (The decree № 220 on materials on a micro-scale basing on the mechanical April 9, 2010) under the Contract № 14.В25.310006, and morphological properties of the components. on June 24, 2013. The approach based on correlation functions is used to formalize the heterogeneous materials’ microstruc- References ture. The set of correlation functions allows to charac- Jiao Y., Stillinger F.H., Torquato S. (2007): Modeling terize and quantify various microscopic properties of heterogeneous materials via two-point correla- the materials including dispersion, clustering and ori- tion functions: Basic principles. Physical Review, entation of inclusions. It is also used for reconstruction 76:031110. of the 3D structure of heterogeneous material in order Kwon YW, Allen DH and Talreja R (eds) (2008): Multi- to avoid repeating costly high resolution imaging tech- scale Modeling and Simulation of Composite Mate- niques during analysis of microstructure (Jiao 2007, Liu rials and Structures. Springer, New York. 2013). Liu Y., Steven Greene M., Chen W. et al. (2013): Com- The suggested methodology implies that mechanical putational microstructure characterization and properties of microstructural components are defined reconstruction for stochastic multiscale material with conventional phenomenological equations and design. Computer-Aided Design 45:65–76 criteria while the effective properties of composite Tashkinov, M. (2014): Statistical characteristics of and characteristics of microscopic deformation fields structural stochastic stress and strain fields in poly- are computed using the elastic and elastoplastic solu- disperse heterogeneous solid media. Computational tions of stochastic boundary value problems (SBVPs) Materials Science 94:44–50 with piecewise constant coefficients equations. The Rasool A, Böhm HJ (2012): Effects of particle shape on multipoint statistical moments and functions of the the macroscopic and microscopic linear behaviors of stochastic stress and strain fields are used as the char- particle reinforced composites. International Journal acteristics of the deformation processes in the compo- of Engineering Science 58:21–34. nents of the material. Their analytical expressions are 403 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 The complex experimental studies of the mechanical proper- ties of reinforcing elements Maria S. Temerova, Valeriy E. Vildeman, Evgeniy V. Lomakin Perm National Research Polytechnic University, Russia, Perm Optimization of properties of composite materials and References their products has brought about the demand for fun- Scardino F., J. Heerlen., S. Kawabata et al. Woven damental studies of properties of filaments and fibres, structural composites: Trans. from English. / Ed. T.- as well as fabrics, under different active external influ- W. And F. Chu Ko. - M .: Mir, 1991.-432 pp., pic. ences. The complexity of the design of such materials Lobanov D.S., Temerova M.S. Features quasi-static provided the basis for the development of questions test yarns and fabrics // Bulletin of Perm National about the mechanical behavior of textile structures Research Polytechnic University. Mechanics. 2013 that characterize the relationship between the struc- № 2. - P. 96-109. ture and properties of materials. Grushetsky I.V., Dimitrienko I.P., Ermolenko A.F. et al. In this paper we propose to study reinforcing materials, Destruction of structures made of composite mate- namely fibres and fabrics, in a complex test. We have rials. Ed. V.P. Tamuzs, V.D. Protasov. - Riga: Zinatne, conducted quasi-static tensile tests on strips of fabric 1986.-264 with. and fibres, impact tensile tests on belts, thread-pulling Vildeman V.E., Babushkin A.V., Tretyakov M.P. et al. tests on fabric, and breaking tests on fabric. Mechanics of materials. Methods and means of The aim of this work was to obtain new data reflect- experimental studies: a tutorial / VE Vildeman [et ing the basic laws of deformation and fracture mecha- al.]; Ed. VE Wildemann. - Perm: Publishing House nisms of woven materials. of Perm. nat. issled. Polytechnic. University Press, From these experiments and analysis of the data ob- 2011. - 165 p. - ISBN 978-5-398-00652-0 tained it can be concluded that the study of woven fab- Fedorov A.E., Samartsev V.A., Gavrilov V.A., Vildemann ric requires further investigation of additional solutions V.E., Slovicov S.V. Experimental study of mechanical and methodological issues. properties of modern surgical absorbable sutures // This work was conducted in Perm National Research Russian Journal of Biomechanics. - T. 13, № 4 (46). - Polytechnic University, with the financial support of 2009. - S. 78-84. the Russian Foundation for Basic Research (grant № 13-08-96016 r_ural_a) and the Government of the Russian Federation (Decree number 220 of April 9, 2010), contract number 14.V25.310006 24 June 2013. Shock loading direction effects on ejection mass and particle sizes of micro-jet from a grooved metal surface Shi Yi-na, Qin cheng-sen Institute of Applied Physics and Computational Mathematics, Beijing, China Metals under shock-loaded conditions can lead to condition and release melting et al. There inevitably complex phenomena depending on the properties of exist many grooves on metal surfaces in the form of the material and initial shock conditions. It has long pits, scratches and machine marks. The micro-jet from been known that the reflection of strong shock waves those grooves may become one kind of main ejection from metal surface can cause a fine spray of matter modes. Up to now, significant efforts have been dedi- particles(ejecta). The phenomenon has attracted much cated to studying on the micro-jet mechanism by ex- attention since being discovered by Walsh and Asay et perimentally and theoretically. Experiment techniques al, due to its importance in shock response of materi- include thin-foils, Asay windows, piezoelectric pins and al interface, and its application in inertial confinement pulsed x-rays. The effects of groove shape, shock wave fusion. rise-time and shock pressure on micro-jet are investi- Previous studies have shown that the formation of gated. Theoretical models and numerical simulations ejecta is very complicated, and ejecta is often caused by on micro-jet have also been carried out, including con- various factors, such as surface microstructure, shock tinuum level and molecular dynamics simulations. Re- 404 Poster Topic G: Fracture mechanics cently, some measured results on ejecta particle sizes for the case of head-on colliding shock loading. The are given, which are also predicted by percolation the- cause may be that the micro-jet have melted or release ory. Some MD simulations investigated nano-scale jet melted. In addition, we discuss the evolution proper- breakup and particle size distribution. However, due to ties of micro-jet matter with time to different groove the complexities, developing a model that predicts the angles. It is valuable for the study on the mechanism amount and particle size of ejecta based on the above of metallic surface fragmentation under shock-loaded micromechanical processe is a difficult problem. condition. In this work, we investigate the dynamic properties of shock-induced surface micro-jet from grooved alu- References minum as regards shock direction and groove angle Asay J.R. (1976): Material ejection from shock-loaded effects. The grooves of 20 µm depth are set on metal free surfaces of aluminum and lead. -Report No. surface. Different loading directions are discussed in SAND-76-0542. detail, with the same impact velocity. One is the case Sorenson D.S., Minich R.W., et al. (2002): Ejecta par- that shock loading is generated along the direction per- ticle size distributions for shock loaded Sn and Al pendicular to metal surface, and another is the case of metals. -J. Appl. Phys., 92(10): 5830. head-on colliding shock loading parallel to the surface. Shi Y.N. & Qin C.S. (2009): The instability and breakup The formation processes of micro-jet from AL surface of stretching metallic Jets. –Chin. J. Theor. Appl. under the above shock conditions are simulated by Mech., 41(3): 361-369. using the code MEPH, which is an independent-devel- Durand O. & Soulard, L. (2012): Large-scale molecular oped multi-material Eulerian hydrocode with a VOF ap- dynamics study of jet breakup and ejecta produc- proach to capture the interface. A new model for the tion from shock-loaded copper with a hybrid meth- particulate spray is developed to study the instability od. -J.Appl.Phys., 111:044901. evolution and fragmentation of micro-jets. Ejecta parti- Dimonte, G. Terrones, G.,et al. (2013):Ejecta source cle diameter is micron, and the particle size distribution model based on the nonlinear Richtmyer-Meshkov of micro-jet is predicted to exhibit a power-law scaling instability., -J. Appl. Phys., 113: 024905. with exponents, in good agreement with Sorenson ex- Li B., Zhao F.P., Wu H.A. & Luo. S.N. (2014): Micro- periment. The results indicate that the total ejected structure effects on shock-induced surface jetting. mass increases significantly, and the ejecta size is less -J. Appl. Phys., 115: 073504. 405 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Poster Topic H: Materials for fission and fusion 406 Poster Topic H: Materials for fission and fusion XRD examination of oxide dispersion strengthened steels ir- radiated by swift heavy ions Andrei Benediktovitch1, Vladimir Uglov1, Svetlana Vlasenko1, Tatiana Ulyanenkova2, Alexander Sohatsky3, Jacques O’Connell4, Vladimir Skuratov4 1Belarusian State University, Minsk, Belarus 2Rigaku Europe SE, Ettlingen, Germany 3Joint Institute for Nuclear Research, Flerov Laboratory of Nuclear Reactions, Dubna, Moscow region, Russia 4Centre for HRTEM, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa Oxide dispersion strengthened (ODS) steels are prom- pole figure measurements and q-2q scans. The q-2q ising functional materials for the IV-th generation nu- scans were measured with Ge(220)x2 monchromator clear reactors. Oxide nanoparticles incorporated into at diffractometer equipped with 9kW rotating anode Fe matrix are expected to improve the swelling and source. The aim of the q-2q measurement was to col- high temperature creep resistance of these alloys ex- lect high quality data for whole profile analysis (Ribarik posed to high radiation damage doses. & Ungar, 2010). The method of convolutive whole One of the source of radiation, which effects remain profile analysis was extended to account for the peak much less studied in comparison with others, are fis- broadening due to distortions of the Fe matrix caused sion fragments, because corresponding structural by oxide nanoparticle. changes can be simulated using dedicated high ener- TEM analysis have revealed that Bi ions induce com- gy heavy ion accelerators only. In this work we have plete amorphization of Y2Ti2O7 pyrochlores composing studied radiation damages in 15CRA-3: Fe-15Cr-2W- nanoparticle population in studied ODS material as a 0.2Ti-0.35Y2O3 ODS steel irradiated by 700 MeV Bi ions. result of multiple latent track overlapping. The room temperature irradiation up to a fluence of 6.15·1012 cm-2 was done at U400 FLNR JINR cyclotron, Reference Dubna. Swift heavy ion induced radiation damages Ribarik, G. & Ungar, T. (2010): Characterization of were characterized using transmission electron mi- the microstructure in random and single crystals by croscopy (TEM) and X-ray diffraction techniques. The diffraction line profile analysis . – Material Science XRD examination included the residual stess analysis, and Engineering A., 528: 112121. Creep and anelasticity of ferritic ODS steel MA956 José Rodolpho de Oliveira Leo1, Amir Shirzadi1, Jan Kowal1, Michael E. Fitzpatrick2 1Materials Engineering Group, The Open University, Milton Keynes, UK 2Faculty of Engineering and Computing, Coventry University, Coventry, UK ODS steels are still regarded as promising materials for its ability of resisting the severe operational environ- advanced nuclear power plants, given the presence, in ment for extended periods of time. the microstructure, of homogeneously distributed ox- During a plant’s lifecycle, variations in demand and ide nanoparticles, which impart high temperature me- stops for maintenance, refuelling or emergencies are chanical strength and resistance against irradiation-in- expected. These conditions impose transients of load duced damage [1]. However, performance of the mate- (or load and temperature), which trigger anelasticity in rial is subjacent to the operational conditions as well as preiously crept materials. It was seen before that ane- to microstructural features, which result from compo- lasticity, characterizad as time-dependent plastic strain sition and fabrication history. recovery, is benefitial to a material, since it increases MA956 is a commercial grade of ferritic ODS steel clas- the creep-rupture life and decreases the creep ductility sified as FeCrAl alloy, due to the 20%Cr and 4.5%Al in [4]. its composition. It is known for its excellent corrosion The work being developed aims at studying to what ex- and creep resistance at high temperature and high an- tent anelasticity takes place in a creep-resistent steel, isotropy of properties, as a consequence of its strongly such as the ferritic ODS MA956. Anelastic response of textured columnar grains [2], [3]. However, the suita- a material is related to intergranular and intragranular bility of this class of steel composites to advanced pow- back stresses, whose origins are associated with dis- er plant components and structures would depend on location motion and interactions in grains and grain 407 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 boundaries. The natural creep strength of this steel, tron diffraction will study the intergranular stress com- then, may be enhanced by recovery phenomena dur- ponent between the textured fibres. ing transients. The characterization of anelastic reponse was found to References be a multidisciplinary approach, envolving comprehen- [1] A. Alamo, V. Lambard, X. Averty, and M. H. Ma- n of dislocation motion through the lattice system and thon, “Assessment of ODS-14%Cr ferritic alloy for investigation of microstructural relevant features. For high temperature applications,” J. Nucl. Mater., vol. this reason, techniques such as EBSD, TEM and netron 329–333, pp. 333–337, 2004. diffraction are employed here, on materials tested for [2] K. Turba, R. C. Hurst, and P. Hähner, “Anisotropic a transient manifested as a full unloading stage during mechanical properties of the MA956 ODS steel creep deformation. characterized by the small punch testing technique,” Preliminary results show that the MA956 is character- J. Nucl. Mater., vol. 428, no. 1–3, pp. 76–81, Sep. ized by {111}<110> and {001}<110> texture systems, 2012. which appear to exert influence on its room temper- [3] T. S. Chou and H. K. D. H. Bhadeshia, “Recrystalliza- ature mechanical response, while high temperature tion temperatures in mechanically alloyed oxide-dis- behaviour seems less affected by its microstructures. persion-strengthened MA956 and MA957 steels,” Samples for anelastic reponse are being tested in the Mater. Sci. Eng. A, vol. 189, no. 1–2, pp. 229–233, longitudinal direction, that is, parallel to the extrusion Dec. 1994. direction, along which the columnar grains are elongat- [4] D. G. Morris, “Anelasticity and creep transients ed, due to its higher strength. Quantitative and quali- in an austenitic steel,” J. Mater. Sci., vol. 13, pp. tative TEM will determine magnitudes of intragranular 1849–1854, 1978. back stresses, associated with dislocations, while neu- Application of Automated Ball Indentation Innovative Tech- nique on the Determination of Mechanical Properties of Nu- clear Structural Materials Jan Štefan1, 2, Radim Kopřiva1, Jan Siegl2 1ÚJV Řež, a. s., Husinec, Czech Republic 2KMAT-FJFI-ČVUT, Prague, Czech Republic Nuclear reactor pressure vessel safety assessment implement innovative testing methods with low re- and lifetime extension are important topics of nuclear quirements on the the necessary volume of the testing power plant management. Through the operation, the material, capable of testing irradiated materials. reactor pressure vessel and its inner components are Automated Ball Indentation (ABI) test is a fully com- subject to high temperature, high pressure, and main- puter-controlled test based on the indentation of a ly the intensive flux of fast neutrons. Microstructural metallic material of a thickness greater than 0.5 mm. changes, proceeding in neutron-irradiated materials, Its purpose is to determine the yield strength and the result in substantial degradation of their mechanical tensile strength of materials in a non-destructive and properties, namely the radiation hardening, the ra- localized fashion. ABI is a simple method since it re- diation embrittlement etc. Therefore, solution of the quires no special device (standard tensile testing ma- nuclear power plant safety assessment requires pre- chine is sufficient). ABI test appears to be a prospective cise information on the degradation of the mechanical mechanical testing method for the irradiated structural properties of the components structural materials. materials’ mechanical properties evaluation. Employ- Mechanical properties of the nuclear power plant ment of the method would contribute to the improve- components’ structural materials are evaluated by ment of mechanical properties evaluation by enlarging testing methods, comprising of surveillance programs. the present data base. Strength properties are evaluated from tensile tests The paper is focused on the description of the employ- results, fracture properties are evaluated either from ment of the ABI technique in the process of reactor Charpy impact tests, or from fracture toughness tests. pressure vessel components structural materials test- However, all the above mentioned methods of me- ing and evaluation at the accredited semi-hot cell test- chanical testing are based on the employment of large ing laboratory of the Mechanical Testing Department specimens. This is connected with high consumption in ÚJV Řež, a. s. The research was done in cooperation of testing material, availability and volume of which is with the Department of Materials, Faculty of Nucle- often limited. Therefore, demand arose to develop and ar Sciences and Physical Engineering, Czech Technical 408 Poster Topic H: Materials for fission and fusion University in Prague (KMAT-FJFI-ČVUT). Comparison of ed in 2013, and the completion of the last stage of the the results of the ABI tests with the results, collected by project is planned for December 2015 with evaluation conventional mechanical testing methods, is depicted. of suitability of the method for the quantification of The results were created within the project mechanical properties of irradiated materials. TA03011266: “Development of innovative semi-de- structive method of high active material evaluation Reference for nuclear reactor components lifetime assessment”. Eliášová, I. – Kopřiva, R. – Falcník, M. (2014): “Hodno- The project is focused on preparation of a certified cení mechanických vlastností strukturních materiálů procedure for quantification of mechanical properties komponent JE využitím semidestruktivních metod.” of structural materials of WWER type reactor compo- (in Czech language) In: All for Power (periodical). nents using miniaturized specimens. The project start- 109-110, ISSN: 1802-8535, Czech Republic Radiation stability of ZrSiN system under the Xe ions irradiation Vladimir Uglov1,2, Vitali Shymanski1, Gregory Abadias3, Gennagy Remnev2, Andrey Suvalov1 1Belarusian State University, Minsk, Belarus 3Institut P’, Poitiers, France Active research in recent years in the study of the struc- nanocrystalline (10 – 30 nm) particles of zirconium ni- ture and properties of nanocrystalline materials have tride ZrN. shown particular promise of composite coatings on the RBS results allowed to determine the concentration basis of ZrSiN, which is characterized by the thermal profiles of the xenon distributed in the ZrSiN coatings, stability of the structure at temperatures up to 1300 °C according to which the maximum concentration of xe- and high mechanical properties [1]. However, there are non increases from 8 to 17 at. % with the dose increas- no any reliable data on the radiation stability of such ing from 5·1016 to 1017 cm-2 (at T=20 ºC). According to structures, which is particularly relevant for their op- the XRD data the lattice parameter of zirconium nitride eration in conditions of high radiation exposure. These ZrN is equal to 0.4572 nm, which corresponds to the materials can be considered as protective materials in lattice parameter of ZrN in the unirradiated system. reactor system of fission. The aim of the present work The implantation of xenon ions at T=800 ºC results in was to study the radiation stability of the ZrSiN system displacement of the maximum concentration to the implanted with Xe ions. depth of about 200 nm that is accompanied by broad- ZrSiN system was formed as a thin film coating on sili- ening of the concentration profile. The lattice param- con substrate by reactive magnetron sputtering of zir- eter of the zirconium nitride ZrN is not changed after conium and silicon target in Ar+N2 (pN = 8.8 mPa) at- xenon ions implantation that can indicate on the stabil- mosphere at temperature of 650 ºC. The power on the ity of the structure for this type of radiation exposure. Zr and Si cathodes was 300 and 250 W, respectively. In The reason for such behavior can be associated with the formed ZrSiN coating the ions of Xe+2 with ener- nanocrystalline particles of zirconium nitride, which gy of 180 keV and the doses 5·1016 and 1017 cm-2 were promotes the migration of radiation-induced defects implanted. The implantation was carried out at room to the interface [2]. (T=20 ºC) and higher (T=800 ºC) temperatures. Thus, it was shown that the structure of coatings ZrSiN, The elemental composition of the ZrSiN system was formed by reactive magnetron sputtering, character- determined on the basis of Rutherford back-scattering ized by the radiation resistance under the xenon ions (RBS), The phase composition was studied by means of (180 keV) irradiation. X-ray diffraction (XRD). The ZrSiN coatings are characterized by uniform distri- References bution of elements across the thickness (600 nm) coat- 1. Musil J., Daniel R., Zeman P., Takai O., Structure and ing, the concentrations being equal to 34 at. % (Zr), 22 properties of magnetron sputtered Zr-Si-N films at. % (Si) and 44 at. % (N). The phase composition of with a high ≥ 25 at.%) Si content // Thin Solid Films. the coating represents by the cubic zirconium nitride 2005. V.478 P.238 ZrN, the lattice parameter of which equals to 0.4572 2. V.V. Uglov, G.E. Remnev, N.T. Kvasov, I.V. Safronov. nm. Diffraction reflections, indicating the presence of Dynamic processes in metal nanoparticles under phases based on silicon have no been identified, how- irradiation. Journal of surface investigation. X-ray, ever, the relation of the concentrations N/Si, being ap- synchrotron and neutron techniques. – 2014. – Vol. proximately equal to 2, allows to suppose [1] an amor- 8, № 4. – P. 703-707. phous matrix of Si3N4 formation with included therein 409 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Poster Topic I: High temperature materials 410 Poster Topic I: High temperature materials Atomistic Simulations of Dislocation-Interface Interactions in the γ/γ’ Microstructure in Ni-base Superalloys Frederic Houlle, Juan Wang, Julien Guenole, Johannes J. Möller, Aruna Prakash, Erik Bitzek Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Department of Materials Science and Engineering, Institute I, Erlangen, Germany The superior strength of single crystalline Ni-base su- with potential properties like the stable and unstable peralloys is mainly caused by the high volume fraction stacking fault energies. In addition to the determina- of the cuboidal L12 ordered γ’ hardening phase which is tion of τc in a pure Ni/Ni3Al system, the influence of Al precipitated in a disordered face-centered cubic γ ma- concentration gradients across the coherent IPB on τc trix. The strengthening effect is rooted in the difficulty as well as the role of Re atoms on dislocation-IPB in- of channel dislocations in the γ-phase to cut into the teractions was investigated. These results can be di- γ’-precipitate. The interaction of dislocations with the rectly used to parameterize e.g. dislocation dynamics γ/γ’ interphase boundary (IPB) is an inherently atom- (DD) simulations. The simulations are compared to 3D istic problem related to the dislocation core structure simulations of the deposition of dislocation segments and energy within the different phases. A quantitative by threading channel dislocations and to the situation determination of the critical resolved shear stress τc in the presence of a misfit dislocation network. The required for dislocations in the γ matrix to penetrate results are discussed in the context of a recent multi into the γ’-phase is therefore difficult to obtain directly scale modeling approach for single crystalline Ni-base from experiments. Although atomistic simulations are superalloys. ideally suited to study this process, only very few, qual- itative studies exist in the literature (Yashiro et al. 2002, References Zhu et al. 2013). Du, J. P., Wang, C. Y. & Yu, T. (2013): Construction and Here we report on a quantitative atomistic study on application of multi-element EAM potential (Ni–Al– dislocation cutting into the γ’ phase. τc is determined Re) in γ/γ′ Ni-based single crystal superalloys. Mod- from quasi-static simulations on infinitely long, straight el. Simul. Mater. Sci. Eng. 21, 015007. dislocation lines interacting with a coherent planar Mishin, Y. (2004): Atomistic modeling of the gamma (100) IPB in a quasi-2D simulation setup using period- and gamma’-phases of the Ni-Al system. Acta Met. ic boundary conditions in line and propagation direc- 52, 1451–1467. tion and 2D boundary conditions with applied forces Yashiro, K., Naito, M. & Tomita, Y. (2002): Molecular in the direction of the glide plane normal. This setup dynamics simulation of dislocation nucleation and allows one to incorporate screw dislocations as well as motion at gamma/gamma’ interface in Ni-based 60° mixed dislocations. The atomic interaction is mod- superalloy. Int. J. Mech. Sci. 44, 1845–1860. eled by two different embedded atom method (EAM) Zhu, Y., Li, Z. & Huang, M. (2013): Atomistic modeling type potentials (Du et al. 2013, Mishin 2004). Studying of the interaction between matrix dislocation and different types of dislocations and using different po- interfacial misfit dislocation networks in Ni-based tentials allows one to evaluate the influence of lattice single crystal superalloy. Comput. Mater. Sci. 70, misfit on the critical cutting stress, and to correlate τc 178–186. 411 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Internal Friction and Shear Modulus Temperature Depend- ence of 9%Cr Ferritic Steel P92 in 25 ÷750°C Temperature Range Elguja Kutelia1 , George Darsavelidze1, Tengiz Kukava1, Temur Dzigrashvili1, Ia Kurashvili1, Fran- cisco J. Perez Trujillo2 1 Georgian Technical University, Tbilisi, Georgia 2 Universidad Complutense de Madrid, Spain The creep rate in practical steels, especially in ferritic machined to a size (1x1x50)mm3 out of bulk coupons, 9%Cr steels (P92), is controlled by the diffusion of sol- previously normalized at 1060°C/20min + tempered at ute atoms rather than vacancies. Chromium is an ex- 770°C/60min. Additional heat treatment after the first ceptional solute because the size difference of Cr ver- measurement was conducted directly in the relaxom- sus α-Fe is very small. Consequently, its diffusion plays eter via annealing at 950°C/20min, after which Q-1(t) an important role in the formation of precipitates in and ƒ2(t) were measured repeatedly. Two maxima of the steel matrix at early stages as well as in the final internal friction were revealed at temperatures 570°C formation of stable phases during a long-term ther- and 650°C, accompanied by shear modulus defects. In mo-mechanical impact. It is also important that the the temperature range 300-750°C reduction of shear above steel contains many minor alloying elements, modulus occur with different rates, depending on pre- and therefore, actual estimation of the diffusion pa- vious heat treatment of the sample. The first maximum rameters and mechanical properties at service tem- is determined to be of relaxation nature, and is char- peratures is not easy in heat-resistant steels. Devel- acterized by the activation energy of ~52000 cal/mol opment of methods of substructural strengthening of and the relaxation time constant equal to 10-14sec. alloys requires a deep insight of the processes of for- According to its activation features, the maximum at mation and stabilization of substructure. The latter ne- 570°C may be attributed to the relaxation rearrange- cessitates use of structure-sensitive methods, among ment of couples of chromium atoms during diffusion which the method of internal friction is most efficient. in α-phase through a Zenner mechanism of relaxation The temperature dependences of Q-1(t) and ƒ2(t) were in the bcc substitution alloys. The temperature of the measured in the relaxometer with the reverse tor- second maximum does not depend on the oscillation sion pendulum at frequencies ~1Hz and amplitudes frequency. Its shape, intensity and temperature con- of deformation 10-5÷10-3 in the temperature range siderably changes in accordance to cooling/heating 25 ÷750°C, with the rate of heating/cooling 2°C/min. rate, amplitude of deformation and annealing time at For the first measurement the samples were cut and temperatures lower than α-γ transformation point. 412 Poster Topic K: Polymer based composites Poster Topic K: Polymer based composites 413 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Research of the Processing Parameters of Three-dimentional Printer and the Product Kunihiro Araki, Goshi Hamabe, Tatsuya Tanaka, Yoshihiko Arao Applied Materials Engineering Laboratory, Faculty of Engineering, Kyoto, Japan “Additive Manufacturing (AM)”, which started from FDM type 3D printer by changing six process parame- the 1980s, is the third manufacturing technology had ters. The parameters such as heat cover, layer height, been gotten by humans, neither the first manufactur- mesh grade, correction of joint, fill density, and speed ing technology: “Removal Processing” nor the second for print moves were studied. Their influences were in- technology: “Forming Processing”, AM is the shaping vestigated by the tensile properties of products and the method of stacking materials in layers. As a result, warpage of products. Five test specimens were made the product can be made, in this way, even though it in each condition. The orders of the experimental were has a too difficult shape to be made by the conven- random sampling because of reducing a constant error. tional methods such as a porous morphology. “Optical In order to reduce the amount of experimental condi- Shaping Method” was the only AM technology when tions, the experiments were carried out using design of the earliest stage of AM. For the past three decades, experiments. And also, the cross sections of specimen the types of AM have dramatically increased. Among after tests were observed by a light microscope, and them, “Fused Deposition Modelling (FDM)” type has their cross section areas were calculated. The investi- been used by anyone in a general office and at home. gation material isn’t only poly lactic acid (PLA), but also The reasons are mainly as follows: first of all, FDM’s PLA/cellulose composite. basic principles are relatively easy to make; secondly, the FDM’s costs are low because expensive parts aren’t References used (e. g. such as laser); and thirdly, the major patents Sood, A. K., R. K. Ohdar, R. K., & Mahapatra, S. S. of FDM had been finished. FDM type of printers can (2010): Parametric Appraisal of Mechanical Property easily make a 3D product with thermoplastic resins and of Fused Deposition Modelling Processed Parts – In: the 3D-CAD data. However, mechanical property of the Materials and Design, 31: 287-295; Elsevier product has a close relationship with process param- Bagsik, A. & Schoppner, V. (2011): Mechanical Proper- eters. So, the suitable parameters should be found in ties of Fused Deposition Modeling Parts Manufac- order to increase mechanical properties of FDM type tured with Ultem*9085 – In: ANTEC 2011; Boston products. Therefore, the purpose of this study is re- Huang, B. & Singamneni, S. (2014): Raster Angle Me- searching of the processing parameters to achieve the chanics in Fused Deposition Modelling – In: Journal product with high mechanical properties and less in of Composite Materials, 0: 1-21; USA deformation. Hayano, S. (2014): Hikari Zoukei kara AM Gijyutsu In this study, tensile test specimens were made using madeno 25 Nen – In: Seikei-Kakou, 26: 141; Japan Supervised Estimation of the Local Glass Fiber Content from 2D X-ray Imaging of Plate-like Parts made from Sheet Mold- ing Compounds Benjamin Bertram, Kay André Weidenmann KIT, Institute for Applied Materials - WK, Karlsruhe, Germany Mechanical Properties of glass fiber reinforced plastics tion of fiber bundles during molding and is likely affect- specifically sheet molding compounds (SMC) is largely ed by the large variety of SMC process parameters in affected by the local fiber architecture which describes use. Therefore the fiber propagation in the flow of the how many fibers occur at some position within the part SMC semi-finished material during molding and the and their orientations. The SMC process is applied in mechanical properties of the cured solid parts are hard the automotive industry to form a discontinuous fib- to predict. Micro computed tomography (µCT) can be er-reinforced polymer. The complex microstructure applied to recover fiber orientations within discontin- of SMC encompasses pores, filler particles and fibers, uous GFRP (Garesci 2013) but only if there is a good whose random orientation is caused by the disaggrega- fiber-matrix contrast. Therefor Al(OH)3 has been used 414 Poster Topic K: Polymer based composites as the filler material. One further implication of µCT is The ground truth is then obtained by incineration of that samples are restricted to a small subsamples on the sample. A prediction model is obtained by line- the millimeter scale that have to be cut out from the ar regression of the known fiber content from image part in order to resolve single fibers. features and local through-thickness. Cross-validation We propose a supervised, X-ray based and non-de- has been used to estimate the prediction error of the structive method to retrieve local fiber volume content model on samples that were unknown in the learning from plate-like parts which is the typical geometry for phase. SMC applications. In (Schipp 1992) the absorption of At the second stage the model can be applied to any X-rays was measured to determine fiber content but no field of vision of the SMC part at coarsely the same fo- locally resolved content map was created and no min- cus-object-distance as the learning samples as long as eral filler deteriorated the fiber-matrix contrast. Un- the local through-thickness can be provided. like in (Schipp 1992) non-linear deviations from Lam- The method has been applied to sections of flat SMC bert-Beer’s law are taken into account by using poly- plate samples (800 mm x 250 mm x 3 mm) and inho- nomial regression and by selecting the image features mogeneities in local fiber content and the influence of which minimize the test error prediction. It is a two the process parameters, i.e. fiber length fiber content step approach that is very common in the context of and layout of the semi-finished mats within the mold. machine learning. At the first stage (“learning phase”) a stochastic estimator is trained from known data pairs References that consist of X-ray image features and some refer- Schipp, C. & Röber, S. & Zachamann, H. G. & Seferis, ence or “ground truth” of the value to be predicted J. C. (1992): Determination of the Fiber Content in i.e. the average fiber content of the specimen. In this Polymer Composites by Means of X-Ray Absorption case image features are computed from radiographs of Measurements. – In: Journal of Applied Polymer flat SMC samples captured with an industry scale cone Science, 44 (9): 1631–1634 beam µCT system. The image features depend not only Garesci, F. & Fliegener, S. (2013): Young’s Modulus on the local fiber content but also on the part thickness Prediction of Long Fiber Reinforced Thermoplas- along the X-ray beams that cover one detector pixel. tics. – In: Composites Science and Technology, 85: Therefore a map of the local through-thickness of each 142–147; pixel had to be computed from the part geometry and the camera parameters of the CT setup. Deformation and fracture of aircraft fibrous polymer com- posites in external actuating factors and high temperature mechanical tests Dmitrii S. Lobanov, Valeriy E. Wildeman, Evgeniy V. Lomakin The Centre of Experimental Mechanics, Perm National Research Polytechnic University, Perm, Russia The aim of this work is investigation of mechanical were carried out on the universal electromechanical properties of fiberglass and carbon fiber reinforced test system Instron 5882 with temperature camber plastics (CFRP) standard plain specimens under shear (-100ᵒC - +350ᵒC) and advanced video extensometer. and bend loading before and after external actuating The work presents results of mechanical tests of fiber- factors and high temperatures were applied. Research glass and CFRP specimens: transverse bending and of physical-mechanical properties of sandwich panels interlaminar shear (short beam method), sandwich pa- with a tubular filler made from fiberglass and CFRP un- nels under tension and compression loading. The effect der tension and compression loading before and after of external polluting operating and high temperature special environments and high temperatures (100ᵒC, on mechanical properties of polymer fiber composite 150ᵒC) were applied too. materials and structures was estimated. Stress-strain Groups of fiberglass and CFRP specimens were soaked diagrams were obtained in tests. in water, oil, gas, hydraulic fluid and petroleum solvent. This work contains analysis of impact contaminants en- This work was carried out in the PNRPU with support vironments and high temperatures on the mechanical of the Government of Russian Federation (the decree properties of polymer fiber composite materials and No. 220 on April 9, 2010) under the Contract No. structures. The methodological issues of using modern 14.B25.310006, on June 24, 2013 and Russian Fund for test equipment for studying the properties of compo- Basic Research (grant No. 13-08-96016 r_ural_a). site materials and structures were considered. Tests 415 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 References estimation of external actuating factors and opera- Babushkin A.V., Wildemann V.E., Lobanov D.S., Tensile tional contamination on operational capability of tests of unidirectional high-filled fiberglass compos- polymer fibrous composite materials // Seventeenth ite at normal and high temperatures, Factory labo- international conference «Mechanics of composite ratory. Materials’ diagnostics, V.76, №7, pp. 57-59, materials»: book of abstracts, Riga, 28 May-01 June 2010. 2012. — Riga, Latvia, 2012. — P. 139. Babushkin A.V., Lobanov D.S., Kozlova A.V., Morev I.D., Lobanov D.S., Babushkin A.V. Deformation and frac- Research of the effectiveness of mechanical testing ture of fibrous polymer composites in thermo-me- methods with analysis of features of destructions chanical impact conditions // Proc. of ECCM15: and temperature effects, Frattura ed Integrita Strut- European Conference on Composite Materials, Ven- turale, Vol.24, pp. 89-95, 2013. ice, Italy, 24-28 June 2012. – Paper ID: 1224. – ISBN Lobanov D., Vildeman V., Babin A., Grinev M. Impact 978-88-88785-33-2. Numerical simulation for developing grounds in support of application of fiber optic sensors for monitoring of compos- ite materials Valery P. Matveenko1, Grigoriy S. Serovaev1,*, Valery, V. Korepanov1, Nataliia A. Yurlova1, Aleksandr N. Anoshkin2, Anatoliy A. Tashkinov2, Gleb S. Shipunov2, Valeriy Y. Zuyko2 1ICMM UB of RAS, Perm, Russia 2PNIPU, Perm, Russia One of the most promising ways of developing intel- it possible to calculate numerically the stress-strain lectual systems which can provide online monitoring fields. of the mechanical state of structures is application Calculations and experiments were conducted on six of sensors embedded into the host structural mate- twelve layered specimens made from glass-reinfor- rial. Due to several advantages, the most valuable of ced plastic with epoxy matrix. Panda optical fiber with which is their small size, optical fiber sensors are the cross-sectional diameter of 0,16 mm was used. most commonly used sensors. In addition, optical fiber The influence of different distribution patterns of op- sensors are highly sensitive, resistant to vibrations and tical fibers through the cross section of specimen and impacts, and are able to work under high temperatures defect known in literature as “resin pocket” was stud- and interact with other smart materials like piezoelec- ied (Jensen 1992). “Resin pocket” is a widely spread tric ones (Udd 2011). type of defect in composite materials with inclusions. The small size of optical fibers makes them easy to The technology of optical fiber inclusion into the com- embed into composite materials at the stage of man- posite structure consists in successive stacking of lay- ufacture. However, differences in their mechanical ers: an optical fiber is put after each resin impregnated characteristics and larger sizes compared to reinforc- layer. Due to this procedure, composite fibers begin to ing composite fibers can have a negative effect on the bend around the optical fiber surrounded by resin mechanical characteristics of the object and may cause The results of numerical and mechanical experiments different defects. have shown that embedded optical fibers do not have Optical fiber is modeled as an inclusion of cylindrical a significant influence on stiffness during tensile tests form. The optical fiber cross-sectional distribution cor- but have a stronger (5 %) effect on stiffness during responds to the real coordinates in the test specimen. bending tests. Besides, the stress-strain field distribu- The coordinates were obtained by special processing tion around optical fiber in the case of resin pocket was of the photographs. The coordinates of optical fiber calculated. through the width of the cross section are distribut- Examples of numerical experiments have been pre- ed randomly during the packaging process. To assess sented to illustrate the process of finding the most ap- the influence of this random distribution on the me- propriate schemes for incorporation of fiber optic sen- chanical characteristics of the specimen, calculations sors allowing registration of the required mechanical were performed, in which the coordinates through the characteristics under static and dynamic loads. width of the model specimen were taken using a ran- The reported study was supported by RFBR, research dom-number generator. projects (No. 14-01-96003, 14-01-96029). Application of the commercial software ANSYS made 416 Poster Topic K: Polymer based composites References Jensen, D.W., Pascual, J., & August, J.A. (1992): Per- Udd, E. & Spillman, W.B.,Jr. (2011): Fiber Optic Sen- formance of graphite/bismaleimide laminates with sors: An Introduction for Engineers and Scientists – embedded optical fibers. I. Uniaxial tension – Smart Udd, E. & Spillman, W.B.,Jr. (eds) 2nd Edition, Wiley, Materials and Structures, 1. 24-30. New York. 417 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Poster Topic L: Lightweight alloys and structures 418 Poster Topic L: Lightweight alloys and structures Ab-initio coarse-grained approach for modeling the two-di- mensional packing structure of solute nanoclusters in Mg- based LPSO phases Hajime Kimizuka1, Shigenobu Ogata1,2 1Department of Mechanical Science and Bioengineering, Osaka University, Osaka, Japan 2Center for Elements Strategy Initiative for Structural Materials, Kyoto University, Kyoto, Japan Mg-based nanolamellar phases of the (hmcn)k type (here, from first-principles calculations based on the densi- h and c represent hexagonal and cubic close-packed ty functional theory. Using the results of the ab-initio motifs, respectively; m, n, and k are integers) formed in CG Monte Carlo calculations, we characterized the ternary Mg-TM (transition metal)-RE (rare-earth met- positional and orientational orders of the attractively al) alloys have recently attracted significant attention or repulsively interacting solute clusters in two dimen- owing to their use in the strengthening of Mg alloys sions, in particular the transformation of the possible and as promising components for designing advanced local ordering patterns of clusters, considering them lightweight structural materials. In such phases (often analogous to two-dimensional colloidal hard-sphere called “long-period stacking ordered (LPSO) phases”), system. The CG model indicated that the Zn-Y clusters the two-dimensional stacking-fault (SF)-type interfaces are arranged in multiple (i.e., at least two) kinds of containing solute atoms can play a significant role in six-fold domain structures with intercluster distances the formation of a nanostructured state with low-en- of 2√3aMg and √19~√21aMg, respectively, in a manner ergy boundaries. As a result, the phases are allowed to consistent with recent scanning tunneling microscopy contain a high density of SFs and exhibit continuously measurements (Kimizuka et al. 2014). The increase in regular nanolamellar structures formed by SF bounda- volume fraction of solute clusters results in close pack- ries, which are an inherent part of their crystal lattice. ing transition of solute clusters, which explains the To understand the fundamental mechanism of the for- steady reduction of radial correlation length between mation of Mg-based LPSO phases, it is important to clusters that was observed in small-angle X-ray scatter- elucidate the essential natures of heterogeneities and ing measurements for Mg85Zn6Y9 LPSO alloys during the medium-range orders in two-dimensional solute-clus- annealing at high temperature (Okuda et al. 2013). ter packing at SF-type interfaces. In this study, we pro- This study was supported by Grant-in-Aid for Scientific posed and established a coarse-grained (CG) modeling Research on Innovative Area (No. 23109004) and the approach based on ab initio calculations for predicting Elements Strategy Initiative for Structural Materials. the equilibrium superlattice structures of solute nano- clusters confined in an atomically close-packed SF. The References approach was used to exploit the intriguing solute-en- Kimizuka, H., Kurokawa, S., Yamaguchi, A., Sakai, A. & riched layers observed in Mg-M-Y (M = Al or Zn) LPSO Ogata, S. (2014): Two-Dimensional Ordering of Sol- phases as examples of multicomponent SF complex- ute Nanoclusters at a Close-Packed Stacking Fault: ions (i.e., interfacial phases). Modeling and Experimental Analysis, Sci. Rep. 4: We investigated the energetic stability and two-di- 7318. mensional ordering with varying packing density of Okuda, H. et al. (2013): Evolution of long-period stack- L12- and E21-type core-shell-like M-Y clusters in the SF, ing order structures on annealing as-cast Mg85Y9Zn6 depending on the temperature and composition, by alloy ingot observed by synchrotron radiation considering effective intercluster interactions derived small-angle scattering, Scr. Mater. 68:575-578. 419 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Surface Nitriding of Titanium Using Atmospheric-controlled IH-FPP Treatment Ota Shumpei1, MURAI Kazue2, OMIYA Msaki2, KOMOTORI Jun2, FUKAZAWA Kengo3,MISAKA Yoshita- ka3, KAWASAKI Kazuhiro3 1Graduate School of Science and Technology, Keio University, Japan 2Department of Mechanical Engineering, Keio University, Japan 3Technical Headquarters, Neturen Co., Ltd., Japan Titanium is superior in corrosion resistance and specific gold. The XRD surface analysis of each kind of the treat- strength, but inferior in wear resistance. Surface hard- ed specimen showed the presence of TiN. TiN peak in- ening by nitriding, for example, gas nitriding1-2), plasma tensity increased as gas flow rate increased. As a result nitriding3-4), laser nitriding5-6) and surface nitriding using of Vickers hardness measurement at cross section, the friction stir processing (FSP) method 7), is effective to value of highest hardness near the surface and the improve wear resistance. The problem of gas nitriding thickness of hardened layer depended on nitrogen gas and plasma nitriding is a longer processing time. Sur- flow rate. In the treatment that nitrogen gas flow rate face nitriding using laser or FSP method is possible to was 130 L/min, the value of highest hardness near the form nitrided layer on titanium surface relatively in a surface was 500HV and the thickness of hardened layer short time, however there are limits on shape and size was 100 µm. These results suggest that the formation of substrate. of nitrided layer on titanium surface is accelerated by In order to form surface nitrided layer in a short time nitrogen gas blow. This means that nitrogen gas blow is without limits on shape or size, we tried nitriding by effective for surface nitriding of titanium. Atmospheric-controlled Induction Heating Fine Particle The surface color of the specimens which were treated Peening (IH-FPP) treatment. Atmospheric-controlled by IH-FPP were not gold. As a result of Vickers hard- IH-FPP treatment system is able to shoot particles at ness measurement at cross section, the value of high- high speed in a controlled atmosphere. In the treat- est hardness near the surface and the thickness of ment, the substrate is heated to higher temperature hardened layer decreased as peening time was longer. by high frequency induction heating. These results suggest that IH-FPP treatment inhibits In this study, pure titanium was nitrided by Atmospher- formation of nitrided layer on titanium surface. ic-controlled IH-FPP treatment. The treatment was performed under nitrogen atmosphere at 900 °C for 3 References minutes. Two types of processes were carried out; one 1) A. Zhecheva et.al., Surface & Coating Technology, is that nitrogen gas flow rate was set 10, 70 or 130 L/ No.201, (2006), pp.2467-2474. min without supplying particles, the other is that peen- 2) Hideki Shibata et. al., Fatigue, Vol.16, (1994), ing time was set 0, 1 or 3min when nitrogen gas flow pp.370-376. was 130 L/min. In the latter, high speed steel particles 3) V. Foquet et.al., Applied Suface Science, No.221, (<45 µm in diameter) was used to FPP. We discussed (2004), pp.248-258. the effects of nitrogen gas flow rate and IH-FPP treat- 4) P. Saillard et.al., Surface & Coating Technology, ment on the formation of the surface nitrided layer. No.45, (1991), pp.201-207. The layer was characterized by macroscopic observa- 5) H.C.Man et.al., Applied Suface Science, No.258, tion, X-ray diffraction analysis (XRD) and Vickers hard- (2011), pp.436-411. ness measurement at cross section. 6) Naofumi Ohtu, Surface & Coating Technology, The surface color of the specimen which was treated No.244, (2014), pp.57-62. at nitrogen gas flow rate of 10 L/min was silver, but the 7) Bo Li et.al., Applied Suface Science, No.274, (2013), color of the specimens treated at 70 or 130 L/min were pp.356-364. 420 Poster Topic X: General mechanical behavior Poster Topic X: General mechanical behavior 421 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Thermal ageing effect on mechanical behavior of polycar- bonate Hamid Bbabou1, Ferhoum Rabah1, Meziane Aberkane1 Laboratory of LEMM, University Mouloud MAMMERI of Tizi-Ouzou, Algeria This work is devoted to the experimental study of ther- R. FERHOUM (2012): Etude expérimental et modéli- mal ageingeffects, with different temperature and du- sation numérique du comportement mécanique du ration, on microstructure and mechanical properties of PEHD à l’état vierge et après vieillissement thermi- amorphous polycarbonate (PC). que. Ph.D, UMMTO. Thetemperature of treatment is fixed at 100 and 150°C, R. FERHOUM, K. HACHOUR, M. ABERKANE, M. HABAK and for three duration 72, 144 and 216 hours; uniaxial- (2014): ANALYSIS OF ANNEALING EFFECT AND MAC- compression tests are conducted at 25 °C, in order to ROSCOPIC TRIAXIALITY ON HIGH DENSITY POLYETH- characterize the mechanical behavior of PC before and YLENE. U.P.B. Sci. Bull., Series B, Vol. 76, Iss. 2. after ageing;the influence of the thermal ageing on the J. M. Hutchinson (1995):Progress in polymer Science material microstructure is characterized using spectra 20, 703-760, 1995. IRTF and micro-hardness analyses. B. Fayolle, L. Audouin and J (2000): Verdu, Polymer It is found that the thermal annealing causes the in- Degradation and Stability 70, 333-340. crease of all properties of material, including Young Steeve COLLIN (2013):Etude du vieillissement des Modulus and yield stress, plastic flow stress, etc. disques optiques numériques recherche de cor- Moreover, the superposition of spectra IRTF shows rélations entre évolution des constituants et perte that the material microstructureinfluenced by increas- de l’information.Ph.D, Blaise Pascal, 2013. ing ofintensity of the bands of vibration of connections V. A. Soloukhin, J. C. M. Brokken-Zijp; O. L. J. Van As- C=C,C-O and C-H; in addition, anincrease of 30% of mi- selen and G. de With (2003): Macromolecules36, cro-hardness was detected after 216 hour of ageing at 7585-7597. 100°C. J. Lu, Y. Wang and D. Shen (2000): Polymer Journal 32, 610-615. References E. L. Cussler (1997):Diffusion Mass Transfer in fluid J Rösler, H Harders, M Bäker (2006):Mechanical be- Systems Second Edition, Cambridge University Press havior of engineering materials. German edition ISBN 0 521 56477 8. published by the Teubner Verlag Wiesbaden, ISBN G. Montaudo, S. Carroccio and C. Puglisi (2002): Jour- 978-3-8351-0008-4. nal of Analytical and Applied Pyrolysis 64, 229-247. Effect of Ultra-violet radiation on the mechanical behavior of PMMA (polymethyl methacrylate) Amirat Boukhalfa, Ferhoum Rabah Department of Mechanical Engineering, Mouloud Mammeri Tizi-Ouzou University, Algeria The investigation we conducted the profile of the me- parameters of aging and to provide elements for un- chanical behavior of polymethyl methacrylate (PMMA) derstanding the mechanism of degradation. the virgin state and what have you exposed to UV ra- Indeed uniaxial compression tests on specimens prac- diation is motivated by what this amorphous polymers tice PMMA has the UV radiation virgin state and after in its good mechanical characteristics and appearance exposure approved the influence of UV irradiation on exile visual make him one of the most industrialized PMMA, for that there was an evolution and plastic used in various application [1], but it has a of the all mechanical material properties (elastic limit, weakness tends to UV radiation, one of the main fac- Young’s modulus ...). tors behind the degradation of the polymer [2]. IR spectroscopy was our use for diagnosis of micro- In this context, our work is based on the validation of structural variations; it has revealed that this degrada- accelerated aging tests acute laboratory correlated tion is caused by damage at the chains cutting effect with the natural exposure to derive the potential of the linkages functions. material in question in terms of the mechanical behav- ior vis-a-vis UV radiation and characterize the critical 422 Poster Topic X: General mechanical behavior References [2] Mercier Jean Pierre., Maréchal Ernest. Traité des [1] OKHAY Nidhal, « synthèse de réseaux polymères matériaux. Chimie des polymères. Synthèse Réac- thermoréversibles par Diels-Alder », Thèse de doc- tions, Dégradation. Tome 13. Chapitre 10. EPFL-édi- torat de l’université Jean Monnet, 2012, p224. teur-Lausane-Suisse. 1996. Dynamic Mechanical Properties of Cortical Bone Depend on Bone Mineral Content Zude Feng, Ting Wang College of Materials, Xiamen University, China Bone is a natural composite material primarily consist- ed that EDTA treatment did not induce a significant ing of an organic phase (mostly Type I collagen) as ma- change to the collagen structure. The results of DSC trix and a mineral phase (hydroxyapatite crystal) as re- measurements indicated that the denaturation tem- inforcement. From the theory of composite materials, peratures of bone were influenced by degree of de- the mineral phase imparts the strength and stiffness to mineralization. The higher denaturation temperature bone, whereas the organic phase the toughness and (239.2 °C) was obtained from the bone specimens in viscoelasticity. Therefore, a better understanding of control group. The results of DMTA revealed that stor- the biomechanical properties of bone and its mecha- age modulus (E´) and loss modulus (E´´) were strongly nism will contribute to further development of novel influenced by mineral content. Higher values of E´ and bone substitute. In this study, the effect of mineral E´´ were observed in control group compared to that content on the visoelastic behavior, collagen structure, demineralized. However, lower values of tan d were and denaturation temperature of cortical bone was in- observed in control group compared to that deminer- vestigated. alized groups. The tan d peak broadened and splitted Fresh bovine cortical bone was used in this investi- into two peaks with the decreasing mineral content. A gation. Forty specimens, 25.0×6.0×0.6 mm (length × shift of peak temperature of tan d to lower tempera- width × thickness) in dimensions, were machined from ture with decreasing mineral content could be ob- the lateral and medial cortices of the midshaft of fresh served. The results were approximately coincidental bovine femora (within 24 hours after slaughter) under with that obtained from DSC assessment. physiological saline irrigation. The specimens were The results of this investigation reveal that the bone randomly divided into four groups: each containing ten mineral content plays an important role on the visco- specimens. The specimens in one group served as the elastic property of bone (i.e. E´ and E´´). The structure control without any treatment. The specimens in the of Type I collagen in bone is long-chained and cross- remaining three groups were immersed in a buffered linked to neighboring collagen molecules. Type I col- (pH 7.3) 0.2 M EDTA solution at 2 °C for 12 hours，24 lagen plays a major role in the viscoelastic nature of hours，and 48 hours, respectively. The solution was bone. In addition, research indicated that the effect of continuously agitated and changed every 24 hours. interaction between matrix and reinforcement in com- Among each group three specimens were used to posite on its viscoelasticity was significant. Due to the conducted DMT analysis, four specimens for apparent intimate combination and interaction between mineral density and mineral content (BMC) measurement, and crystal and collagen fibers in sub-nanometer scale, the three specimens for collagen structure characterization mineral crystal has a significant effect on bone’s visco- and thermal analysis. The dynamic-mechanical-ther- elasticity. The presence of mineral phase will reduce mal analysis was carried out under a single cantilever the movability of collagen chains. Besides, since the load scheme. Temperature was scanned from 20 °C to higher E´´ value means improvement of bone’s ability 300 °C at 2 °C min-1 under a loading frequency of 1 Hz. to absorb impact energy in accident, the result of this The collagen structure was characterized by infrared investigation suggests that dynamic mechanical prop- spectrometer (FTIR). The denaturation temperature of erty is the same important parameter as elastic modu- intact and demineralized bone was assessed by a dif- lus and ultimate strength in evaluating bone’s quality. ferential scanning calorimeter (DSC). However, the underlying mechanism is not very clear The statistical analysis revealed that there were statis- because the complicate interaction between mineral tically significant differences in apparent density and crystal and collagen fibers. Further study will be re- mineral content of bone between the different test quired to explore this issue. groups (P < 0.01). The results of FTIR analysis indicat- 423 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 Study of concretes and mortars made with metallic fibers Souad Kherbache, Karim Moussaceb, Nedjima Bouzidi, A. kader Tahakourt University A. Mira, Departement of Civil Engineering, Bejaia, Laboratory of Genius of the Building and of Archi- tecture, Aleria The use of fibers in building materials; particularly in With the intention of highlighting the influence of the mortar and concretes a more and more used technol- metallic fibers on the properties of concretes and of ogy, for several reasons, is ecological, either economic, mortar, cement was substituted by different percent- or to improve some properties in the hardened or cool ages. state. Indeed, the use of the metallic fibers in substitu- Purpose aimed in the present job is to search optimum tion of cement allows a reduction of the consumption in rate of substitution of the cement by the metallic of the clinker by contributing, in a considerable way, fibers which will give at the same time a good resist- to reduce the energy price and to regulate problems ance to compression and to inflexion, and acceptable linked to the pollution of environment by the CO2. shrinking and inflation. As generally known, the sector of building materials is the third biggest sector issuing CO2 in industry, world- References wide (Yu, Spiesz & Brouwers 2014). They say that the R.Yu, P. Spiesz, H.J.H. Brouwers (2014): Mix design and production of cement represents 7 % of all programs properties assessment of Ultra-High Performance of anthropogenic CO2 (Capros, Kouvaritakis, Mantzos Fiber Reinforced Concrete (UHPFRC), Cement and 2001). concrete Research, Volume 56, Pages 29-39. The concrete is a composite material with a low resist- P. Capros, N. Kouvaritakis, L. Mantzos (2001): Eco- ance to traction and low tension (Uygunoglu 2008). nomic evaluation of sectorial emission reduction Generally the addendum of fibers in the concrete mix- objectives for climate change top-down analysis ture can considerably improve the properties of engi- of greenhouse gas emission possibilities in the EU, neering of the concrete such as; inflexion, tiredness Contribution to a study for DG environment. Euro- and force of abrasion, the capacity of distortion, hard- pean commission. ness and capacity holder after cracking (Mohammadi, Uygunoglu T. (2008): Investigation of microstructure Singh , Kaushik 2008) & (Yazıcı, Inan, Tabak V 2007) and flexural behavior of steel fiber reinforced con- Although the concrete is the material of building most crete. Mater Struct; 41(8):1441–9. used on earth, this material always has some prob- Mohammadi Y, Singh SP, Kaushik SK. (2008): Proper- lems; he has a good resistance against efforts of com- ties of steel fibrous concrete containing mixed fibers pression, but a resistance to very low traction. Under in fresh and hardened state Construct Build Mater, duress of traction, the concrete cracks easily and al- 22(5):956–65. most any ductility. Medium classic to resolve this prob- Yazıcı S, Inan G, Tabak V. (2007): Effect of aspect lem can be the application of strengthening by fibers. ratio and volume fraction of steel fiber on the me- The other solution is the application of different types chanical properties of SFRC. Construct Build Mater fibers in the concrete, this material is then called «the 21(6):1250–3. concrete of fibers». Effect of Strain-Rate on Tensile Properties of Nuclear Piping Materials at RT and 316oC Jin Weon Kim, Myung Rak Choi Dept. of Nuclear Eng., Chosun Univ., Gwangju, Korea The integrity of piping components in nuclear power at quasi-static monotonic loading condition (DeGras- plants (NPPs) should be maintained under seismic con- si,2008). However, the seismic loading has random, dition as well as normal operating condition. Thus, it dynamic, and cyclic characteristics. Some studies re- is important to reliably evaluate the integrity of piping ported that the deformation and fracture behaviors of components under seismic loading condition. In the material under dynamic and cyclic loading were much existing evaluation procedure, the integrity is evaluat- different from those under quasi-static monoton- ed based on the magnitude of seismic load given by lin- ic loading and the dynamic and cyclic loading effects ear-elastic analysis and mechanical properties tested depended on type of materials (Hopper, 1996; Boyce, 424 Poster Topic X: General mechanical behavior 2009). Thus, it is necessary to investigate the effects of stainless steel. It is concluded that at operating tem- dynamic and cyclic loads on the mechanical properties perature of NPPs tensile properties of SA508 Gr.1a low of nuclear piping materials to ensure the reliability of alloy steel are sensitive to strain-rate and show abnor- integrity evaluation under seismic loading conditions. mal strain-rate dependence. But the tensile properties Therefore, this study conducted a series of tensile of SA312 TP316 stainless steel are less sensitive to tests on SA508 Gr.1a low alloy steel and SA312 TP316 strain-rate at 316oC. stainless steel piping materials under various strain- rates ranging from 3.95x10-4 to 10s-1. The tests were Acknowledgments conducted at RT and operating temperature of NPPs This research was supported by National Research Foun- (316oC). SA508 Gr.1a low alloy steel and SA312 TP316 dation of Korea(NRF) funded by the Ministry of Science, stainless steel are materials commonly used in prima- ICT and Future Planning(NRF-2013M2A8A1040924) ry piping system of NPPs. From the results of tensile and the Nuclear Power Core Technology Development test, the effect of strain-rate on tensile properties of Program of the Korea Institute of Energy Technology nuclear piping materials was investigated for each pipe Evaluation and Planning (KETEP), granted financial re- material. source from the Ministry of Trade, Industry & Energy, The results showed that the tensile properties for both Republic of Korea(20141520100860). pipe materials were compliant with typical strain-rate dependence at RT; i.e., the strength increased and the References ductility decreased as strain-rate increased. At 316oC, DeGrassi, G., Nie, J., Hofmayer, C. (2008): Seismic however, the dependence was different from the typi- Analysis of Large-Scale Piping Systems for the cal strain-rate dependence. Tensile strength as well as JNES-NUPEC Ultimate Strength Piping Test Program, elongation of SA508 Gr.1a low alloy steel decreased as NUREG/CR-6983. strain-rate increased. Reduction of area was non-lin- Hopper, A., Wilkowski, G., Scott, P., Olson, R., Rud- early varied with strain-rate; it decreased initially and land, D., Kilinski, T., Mohan, R., Ghadiali, N., Paul, then increased with increase in strain-rate. Thus, re- D. (1996): The Second International Piping Integrity duction of area at 10s-1 was almost the same as that at Research Group (IPIRG-2) Program – Final Report, 3.95x10-4s-1. These characteristics are associated with NUREG/CR-6452, BMI-2195. dynamic strain aging phenomenon appeared in ferrit- Boyce, B.L., Dilmore, M.F. (2009): The dynamic tensile ic steels at 200-300oC (Baird, 1971). For SA312 TP316 behavior of tough, ultra-strength steels at strain- stainless steel, the variations of strength, elongation, rates from 0.0002s-1 to 200s-1, Int. J. Impact Eng., 36, and reduction of area with strain-rate were negligi- 263-271. ble at 316oC. Regardless test temperatures, the strain Baird, J.D, (1971): The effects of strain aging due to hardening rate was nearly independent of strain-rate interstitial solutes on the mechanical properties of for SA508 Gr.1a low alloy steel, while it gradually de- metals, Metall. Reviews, 16, 1-18. creased with increasing strain-rate for SA312 TP316 Variation of Mechanical Properties in the Pipe Bends Fabri- cated by High-frequency Induction Bending Jin Weon Kim1, Mi Yeon Lee1, Young Jin Oh2, Heung Bae Park2, Kyung Su Kim2, Tae Soon Kim3 1Dept. of Nuclear Eng., Chosun Univ., Gwangju, Korea 2Power Engineering Research Institute, KEPCO E&C, Kyoungki, Korea 3Center for Research Institute, KHNP, Daejon, Korea The use of pipe bends fabricated by high-frequency in- of the pipe bend would be different from those of duction bending gradually increases in piping systems original pipe and show spatial variation within pipe of power plants and shipbuilding plants because of bend. Therefore, it is necessary to investigate the lo- several advantages such as eliminating welds between cal mechanical properties of pipe bend fabricated by elbow and pipes, improving flexiblility of pipe rout- high-frequency induction bending. In particular, the ing, and less costs (Lee 2011, Lee 2012). Recently, it investigation is important for piping systems applying is attempted to use the pipe bends for piping systems leak-before-break (LBB) concept because the lower of nuclear power plants. However, high-frequency in- bound mechanical properties should be used for LBB duction bending could locally change microstructure evaluation (USNRC 1984). of pipe material induced by local heating and rapid This study carried out a series of tensile tests to inves- cooling (Lee 2012). Thus, the mechanical properties tigate the local mechanical properties of SA312 TP316 425 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 stainless and SA335 P22 ferritic steel pipe bends fabri- much different from those of original straight pipe. The cated by high-frequency induction bending. The tests observation of microstructures revealed that the me- were conducted at both ambient temperature and op- chanical properties of TP316 stainless steel pipe bend erating temperature of piping systems (316oC for TP316 were strongly affected by dynamic recrystallization stainless steel pipe bend and 292oC for P22 ferrtic steel followed by plastic strain. However, the properties of pipe bend). The specimens were machined from the P22 ferritic steel pipe bend were affected by heating various locations in the pipe bend, including intrados, and cooling process rather than plastic strain applied extrados, and crown regions of bend, start and end of by bending process. bend, and straight pipe. Also, microstructures were ob- served at different locations for both pipe bends using Acknowledgments optical microscope (OM) and scanning electron micro- This work was supported by the Nuclear Power Core scope (SEM). Technology Development Program of the Korea Insti- For both pipe materials, the pipe bends always showed tute of Energy Technology Evaluation and Planning higher strength and lower ductility than original (KETEP), granted financial resource from the Ministry straight pipe. This means that the strength was in- of Trade, Industry & Energy, Republic of Korea. creased and the ductility was decreased by high-fre- quency induction bending for both pipe materials. For References TP316 stainless pipe bend, the change in the strength Lee, H., Bae, J., Kim, M., and Kim, C., (2011): Optimal and ductility was almost proportional to the degree of Design of Pipe Bending Based on High-Frequency strain applied by bending process. Thus, the change of Induction Heating Using Dynamic Reverse Moment, mechanical properties was considerable at center of Int. J. Prec. Eng. & Manuf., 12, 1051-1058. bend than at start and end of bend region. Within the Lee, Y., Lim, J. & Moon, Y. (2012): Mechanical Char- center of bend region, the highest strength and low- acteristics of Low-Carbon-Steel Pipe Bent by Local est ductility appeared at intrados region rather than Induction Heating with Small Bending Radii, Mat. extrados. For P22 ferritic pipe bend, however, the me- Trans., 53, 847-852. chanical properties were nearly independent of loca- USNRC (1984): Evaluation of Potential for Pipe Breaks, tions within pipe bend, although the properties were NUREG-1061, Vol.3 Modeling and observation of compressive behaviors of ani- sotropic aluminum cellular structures based on the Voronoi tessellation concept Sang-Youn Park1, Byoung-Ho Choi1 Seung Ki Moon2, Il-Hyuk Ahn 2 1 School of Mechanical Engineering, Korea University, Seoul, Republic of Korea 2 School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore In these days, foams have been used in many industri- facotrs, plastic collapse, elastic and/or plastic buckling, al applications due to many mechacnical and physical brittle fracture can occur as a major failure mechanism. benefis comparing with conventional solid structure. Ragrading the cell structure of foams, many artifical Especially, it has been known that foams have a wide shapes, such as hexagon honeycomb, triangle, square range of applications such as noise and vibration ab- and so on., have been introduced and commercially sorption, impact and static energy absorption, thermal produced. However, these models are usually ideal, so insulation and so on. Foams are usually having a high foams with random celluallar structures can not ana- stiffness-weight ratio, so they can be a good alternative lyzed by those models. for oversigned heavy structures. Because of their appli- In this paper, Voronoi tessellation concept was adapt- cations, compressive loads can be a major loading con- ed too make a mathematical model to describe radom ditions, so the understanding of compressive load-dis- structures of foams. Originally, Voronoi theory was placement of foams is practically important. Gibson used to divide the jurisdiction. For engineering re- and Ahsby insist that foam`s compressive behavior searches of random cellular structures, this model can is depending on many physical and material factors be very useful. Here is the brief description of generat- such as base material, shape and size of their cellular ing Voronoi cells : First, seeds are randomly scattered. structure, the homogeneity of cells and so on. Depend- Based on this seeds, perpendicular bisector can be pro- ing on the combination of such physical and material duced. Then Voronoi cell is produced. 426 Poster Topic X: General mechanical behavior Hoever, the method for scattering seed based on con- and compared. The relationship between key physical ventional Voronoi theory may bring another problems. properties and relative density is also discussed. In ad- Seed`s distribution is too irregular, the geometric sig- dition, the anisotropy of cellular structures can be an nificance of produced cells can be weak. So, in this important factor to determine mechanical properties paper, the concept of centroidal Voronoi tessellation of the cellular structures. So, various anisotropic cell (CVT) is adopted. CVT is a scattering method which structures are generated, the variation of compressive uses cell`s center of mass. When iterations of gener- behaviors is discussed. ating Voronoi cells is progressed, cell sizes becomes Finally, experiments of selected cell structures which uniform asympotically. In this paper, the number of are generated by a 3-D printer using alluminum alloy iterations are 1,5,10 and 30 to generate the various are performed. The experimental results are com- random cell structures. At the same time, conventional pared and discussed with the results obtained from cell strucrures such as hexagon, square and triangle are numerical analysis. also generated. After making various 2-D cells using a commercial References program, i.e. Matlab, the cells are extruded to mim- Lorna J. Gibson and Michael F.Ashby. (1997):Celluar ic common Honeycomb-like structures. Elasto-plastic solids:structures and properties – second edition, ; compressive behaviors of various aluminum foams are CAMBRIDGE. numerically analyzed by Abaqus, one of popular com- Wolburg, J. (1969): Uniaxial stress–strain behavior mercial programs for finite element analysis (FEA). Fail- of aluminium alloy foams. – Acta Materialia 47,8 ure mechanisms as well as load-displacement behav- :2323-2330;Cambridge. iors of various structures are discussed are discussed Influence of the addition of cooked and crushed clay on the mechanical strength of a self-compacting concrete Fatiha Soudi, Nasser Chelouah, Tiziri Bezzi Laboratoire Génie de Construction et Architecture (LGCA) Self-compacting concrete (SCC) are very fluid concretes References that are taking place under the effect of gravity with- R. D. Toledo Filho et al. Potental for use of crushed out addition of vibration. waste calcined-clay brick as a supplementary Cement production, essential for the production of cementitious in Brazil. Cement and Concrete concrete in general, is accompanied by a release of Research, Vol 37; pp 1357-1365, 2007. a large amount of CO2 (greenhouse gas). The aware- B.B. Sabir, S. Wild, J. Bai, Metakaolin and calcined ness of the harmful effects of such emissions into clays as pozzolans for concrete: a review, the atmosphere favors more new environmental Cement and Concrete Composites. Vol 23; approaches to be taken into account in the formu- pp441-454; 2001. lation of concrete and more of the specifications. R. D. Toledo Filho, B.B. Americano, E.M.R. Our goal is to make “green” SCC based on miner- Fairbairn, J.S Rolim, J. Farias Filho, Potential of al additions. For this, we chose to use two miner- crushed waste calcined-clay brick as partial al additions: the Cooked and Crushed Clay (CCC) replacement for Portland cement, in : V.M. and the limestone filler tiles from sanding waste. Malhota(E.d), Third Intenational Symposium on The CCC is used in substitution for a certain Sustainable Development of Cement and amount of cement. Limestone fillers are used Concrete, ACI SP-202 (2001) 147-156. to obtain the required properties of fresh SCC. N. KAIDI et al. Un béton performant et durable a The choice of CCC as a mineral addition is very interesting base de la pouzzolane naturelle de Beni Saf. 3 because its production emit very little CO2 in the atmos- ème séminaire sur les technologies du béton ; phere and it has very good pozzolanic properties. The use 17 et 18 septembre 2006, Alger. of limestone fillers as to it leverages an industrial waste. E. Badogiannis, S. Tsivilis. Exploitation of poor Self-compacting concrete containing varying propor- Greek kaolins : Durability of metakaolin tions of CCC (0%, 5%, 10%, 15% and 20%), boiled for 1 concrete .Cement and Concrete Composites. hour at 750 ° C and limestone fillers rates were studied. Vol 31; pp128-133; 2009. The compressive strength results show that the optimum M. ABIB et. al. L’influence du métakaolin sur les pro- ratio is 10% CCC. Furthermore, it is found that the use of prié- tés du béton; 3 ème séminaire sur les technol- CCC and limestone fillers reduces shrinkage deformation. ogies du béton ; 17 et 18 septembre 2006, Alger. 427 ICM 12 – 12th International Conference on the Mechanical Behavior of Materials, Karlsruhe, 10–14 May 2015 E. Badogiannis, G. Kakali, G. Dimopoulou, E. Rafat Siddique, Juvas Klaus. Influence of Chaniotakis, S. Tsivilis, Metakaolin as a main metakaolin on the propreties of mortar and cement constituent: exploitation of poor Greek concrete: a review. Applied Clay Science, vol 43; kaolins. Cement and Concrete Composites. Vol pp 392-400; 2009. 27; pp197-203; 2005. Retained Austenite: Non Destructive Analysis by using X-Ray according to ASTM 975-03 M. Michiel van der Mey Managing Director of Greensilver Germany GMBH Retained austenite as a crucial parameter that affects tial for changes in the dimension of the part leading to the operating performances of mechanical parts, must crack initiation. be under control. Physical properties depend on different phases The X-Ray diffraction technique allows to measure it in amount, if phase transformation occurs also these a non destructive way. Standard practices to measure physical properties change. retained austenite are laid down in ASTM 975-03. The presentation‘s aim is to demonstrate how the ARE Retained Austenite affects fatigue strength, toughness, X can easily determine retained austenite by using X hardness, yield strength and machinability. Retained Ray and as a consequence to control and tune the pro- austenite can further transform during the service life duction steps. of the product into other phases, providing the poten- 428 Poster Topic X: General mechanical behavior 429