Browsing by Author "Fitzpatrick, ME"
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- ItemApplication of the work of indentation approach for the characterization of aluminium 2024-T351 and Al cladding by nanoindentation(Springer, 2009-02) Khan, MK; Hainsworth, SV; Fitzpatrick, ME; Edwards, LNanoindentation has been used to characterize the mechanical properties of aerospace-grade Al2024-T351 with and without a clad layer of pure aluminium. The clad layer is introduced by means of a roll-bonding process which can cause significant work-hardening of the material in the clad layer. The hardness and Young’s modulus of the pure aluminium and the Al2024 have been determined by a number of methods, including the traditional Oliver and Pharr method, and a number of other methods, including direct measurement of the indentation by atomic force microscopy, and evaluation of the work of indentation. The Oliver and Pharr method was found to underestimate the area of contact as it did not include the area of piled-up material around the indentation periphery. This gave a corresponding overestimation of both hardness and modulus. The area of the indentation measured by atomic force microscopy was similarly found to underestimate the contact area owing to relaxation of material around the indent between indentation and imaging. The work of indentation approach was found to give good agreement between the hardness calculated by nanoindentation and those found in the literature. © 2009, Springer.
- ItemCombined experimental and finite element approach for determining mechanical properties of aluminium alloys by nanoindentation.(Elsevier, 2010-10) Khan, MK; Hainsworth, SV; Fitzpatrick, ME; Edwards, LAluminium alloys for the aerospace industry are often clad by roll-bonded aluminium to improve corrosion resistance. The clad layer is of the order of 100 μm in thickness and it is difficult to determine the mechanical properties of this layer by conventional mechanical testing techniques. Nanoindentation is ideally suited to determining the elastic and plastic properties of such layers and here we report on a combined approach using experimental nanoindentation and finite element analysis to extract yield stress and strain hardening exponent for an Al-clad system. The approach used was calibrated against results for an Al 2024-T351 alloy, where conventional mechanical testing data was available. For the Al 2024-T351, a forward analysis was used for extraction of load–displacement curves at different indentation depths with the help of elastic–plastic properties obtained from tensile testing. For a 100 μm clad layer of pure aluminium on Al 2024-T351, reverse analysis was used for extraction of elastic–plastic properties from a single indentation test. A yield stress of 110–120 MPa and a value of 0.075–0.1 for the work hardening exponent was obtained for the Al cladding. Nanoindentation properties including maximum load of indentation, contact depth, area of contact and pile-up obtained from the forward and reverse analyses showed excellent agreement with the experimental results. © 2010, Elsevier Ltd.
- ItemDetermination of the residual stress field around scratches using synchrotron x-rays and nanoindentation.(Trans Tech Publications, 2009-11-10) Khan, MK; Fitzpatrick, ME; Edwards, L; Hainsworth, SVThe residual strain field around the scratches of 125µm depth and 5µm root radius have been measured from the Synchrotron X-ray diffraction. Scratches were produced using different tools in fine-grained aluminium alloy AA 5091. Residual stresses up to +1700 micro-strains were measured at the scratch tip for one tool but remained up to only +1000 micro-strains for the other tool scratch. The load-displacement curves obtained from nanoindentation were used to determine the residual stresses around the scratches. It was found that the load-displacement curves are sensitive to any local residual stress field present and behave according to the type of residual stresses. This combination of nanoindentation and synchrotron X-rays has been proved highly effective for the study of small-scale residual stresses around the features such as scratches. © 2020 by Trans Tech Publications Ltd.
- ItemEffect of frequency on high-temperature fatigue crack growth in a silicon carbide reinforced silicon nitride composite(Elsevier, 2013-02-01) Moffatt, JE; Fitzpatrick, ME; Edwards, LA detailed study on a silicon nitride reinforced with silicon carbide whiskers, Si3N4SiCW, has been undertaken at elevated temperature during static and dynamic loading at increasing K and ΔK respectively. It is shown that cyclic sub-critical crack growth rates are lower than static crack growth rates. The increased crack growth rate during static far field loading is attributed to the stress relaxation of the inter-granular glass phase which allows time-dependent processes to occur ahead of the crack tip which lead to enhanced sub-critical crack growth rates. During cyclic fatigue the glass phase has insufficient time to relax and glassy ligaments are able to bridge the crack wake thereby shielding the crack tip from the full force of the applied load. Also, at particular temperatures, bridging between the surfaces of the crack wake by the inter-granular glass phase results in increased strength and fatigue retardation. The extent of ‘crack wake healing’ is shown to be time and temperature dependent. The viscosity of the glass phase is directly related to the temperature and the bonding force associated with glass phase bridging is observed to reduce with increasing temperature. The results from a previous study at room temperature are compared to those found during this investigation. © 2012, Elsevier Ltd.
- ItemEffect of tool profile and fatigue loading on the local hardness around scratches in clad and unclad aluminium alloy 2024.(Elsevier, 2009-12-15) Khan, MK; Fitzpatrick, ME; Hainsworth, SV; Edwards, LNanoindentation has been used to study the hardness changes produced by scratching of aluminium alloy AA2024, with and without a clad layer of pure aluminium. The hardness was mapped around scratches made with diamond tools of different profiles. One tool produced significant plastic damage with associated hardening at the scratch root, whilst the other produced a ‘cleaner’ cut with no hardening. The different behaviours are attributed to whether the tool makes the scratch by a ‘cutting’ or a ‘ploughing’ mechanism. The degree of plastic damage around the scratches has been correlated with peak broadening data obtained using synchrotron X-ray diffraction. There was no change observed in the local hardness around the scratch with fatigue loading. © 2009, Elsevier Ltd.
- ItemEffect of weld residual stresses and their re-distribution with crack growth during fatigue under constant amplitude loading(Elsevier, 2010-04) Liljedahl, CDM; Zanellato, O; Fitzpatrick, ME; Lin, J; Edwards, LIn this work the evolution of the residual stresses in a MIG-welded 2024-T3 aluminium alloy M(T) specimen during in situ fatigue crack growth at constant load amplitude has been measured with neutron diffraction. The plastic relaxation and plasticity-induced residual stresses associated with the fatigue loading were found to be small compared with the stresses arising due to elastic re-distribution of the initial residual stress field. The elastic re-distribution was modelled with a finite element simulation and a good correlation between the experimentally-determined and the modelled stresses was found. A significant mean stress effect on the fatigue crack growth rate was seen and this was also accurately predicted using the measured initial residual stresses. © 2010, Elsevier Ltd.
- ItemEnergy-resolved neutron imaging for reconstruction of strain introduced by cold working(MDPI, 2018-02-28) Tremsin, AS; Kockelmann, W; Kelleher, JF; Paradowska, AM; Ramadhan, RS; Fitzpatrick, MEEnergy-resolved neutron transmission imaging is used to reconstruct maps of residual strains in drilled and cold-expanded holes in 5-mm and 6.4-mm-thick aluminum plates. The possibility of measuring the positions of Bragg edges in the transmission spectrum in each 55 × 55 µm2 pixel is utilized in the reconstruction of the strain distribution within the entire imaged area of the sample, all from a single measurement. Although the reconstructed strain is averaged through the sample thickness, this technique reveals strain asymmetries within the sample and thus provides information complementary to other well-established non-destructive testing methods. © 1996-2021 MDPI
- ItemEvolution of crack-tip stresses during a fatigue overload event.(Elsevier, 2010-06) Steuwer, A; Rahman, M; Shterenlikht, A; Fitzpatrick, ME; Edwards, L; Withers, PJThe mechanisms responsible for the transient retardation or acceleration of fatigue crack growth subsequent to overloading are a matter of intense debate. Plasticity-induced closure and residual stresses have often been invoked to explain these phenomena, but closure mechanisms are disputed, especially under conditions approximating to generalised plane strain. In this paper we exploit synchrotron radiation to report very high spatial resolution two-dimensional elastic strain and stress maps at maximum and minimum loading measured under plane strain during a normal fatigue cycle, as well as during and after a 100% overload event, in ultra-fine grained AA5091 aluminium alloy. These observations provide direct evidence of the material stress state in the vicinity of the crack-tip in thick samples. Significant compressive residual stresses were found both in front of and behind the crack-tip immediately following the overload event. The effective stress intensity at the crack-tip was determined directly from the local stress field measured deep within the bulk (plane strain) by comparison with linear elastic fracture mechanical theory. This agrees well with that nominally applied at maximum load and 100% overload. After overload, however, the stress fields were not well described by classical K fields due to closure-related residual stresses. Little evidence of overload closure was observed sometime after the overload event, in our case possibly because the overload plastic zone was very small. © 2010, Elsevier Ltd.
- ItemEvolution of residual stresses with fatigue crack growth in integral structures with crack retarders(Elsevier, 2009-10-15) Liljedahl, CDM; Fitzpatrick, ME; Edwards, LBonded straps are investigated for their ability to retard a growing fatigue crack in metallic structures. The evolution of the residual stresses in the vicinity of the strap with fatigue crack growth has been studied. Cracks were grown in single edge-notched tension (SEN(T)) specimens reinforced with either a titanium or a carbon fibre reinforced plastics (CFRP) strap. The residual stress evolution has been measured in situ during crack growth using neutron diffraction, and modelled with a finite element approach. The peak residual stresses induced by the mismatch of the coefficient of thermal expansion between the strap and plate materials were seen to be fairly constant with crack growth. Good correlation between the experimental and the modelling results was found, except at very long crack lengths for a specimen that exhibited considerable fracture surface roughness at long crack lengths. The difference was attributed to wedging of the fracture surface changing the expected stress state, rather than any effect of the strap. © 2009, Elsevier Ltd.
- ItemFatigue and fracture of a 316 stainless steel metal matrix composite reinforced with 25% titanium diboride(Elsevier, 2013-03-01) Bacon, DH; Edwards, L; Moffatt, JE; Fitzpatrick, MEFatigue and fracture mechanisms have been studied in a steel-based metal matrix composite (MMC),comprising a 316L austenitic matrix reinforced with 25 wt.% particulate titanium diboride (TiB2). The fracture toughness was determined in the as-HIPped condition as being slightly below 30 MPapm. Fatigue crack growth rates have been determined, and corrected for the effects of crack closure. The fracture surfaces have been studied to determine the mechanisms of damage during crack advance, which are determined as matrix fatigue, reinforcement particle fracture, and ductile rupture of the matrix. We show that the occurrence of damage mechanisms during fatigue of the material is linked to Kmax, rather than to DK. This is rationalised in terms of a semi-cohesive process zone within the monotonic plastic zone ahead of the crack tip. © 2012, Elsevier Ltd.
- ItemFull field measurement of plastic flow properties in a multi-pass austenitic stainless steel weld specimen.(American Society of Mechanical Engineers (ASME), 2008-07-27) Ganguly, S; Turski, M; Fitzpatrick, ME; Edwards, L; Smith, MC; Bouchard, PJKnowledge of constitutive material stress strain properties is important for reliable prediction of weld residual stress fields using analytical stress simulation techniques. The present work investigates the surface stress strain behaviour of a 3-pass groove-welded austenitic stainless steel disc. A relatively novel electronic speckled pattern interferometry (ESPI) technique was employed to monitor the surface deformation pattern across the weld, HAZ and parent metal of the specimens with very high spatial resolution. The deformation data was then analysed to determine the constitutive stress-strain property across the welded specimen. The analyses show very different patterns of proof stress variation across the pass I and pass III weld metal. The accumulated plastic strain in the pass I weld metal resulted in an increase of the 0.2% PS value by 175 MPa. © 2008 ASME
- ItemIncorporation of Yttria particles into 410L stainless steel by a power metallurgy route(Springer, 2014-04-11) Zeybek, A; Pirfo Barroso, S; Chong, KB; Edwards, L; Fitzpatrick, MEAddition of yttria to steels has been proposed for the fabrication of oxide-dispersion-strengthened materials for nuclear power applications. We have investigated materials prepared from 12 Cr martensitic stainless steel, AISI 410L, produced by powder metallurgy. Materials were produced with and without yttria addition, and two different sizes of yttria were used, 0.9 µm and 50 nm. Tensile and mini-creep tests were performed to determine mechanical properties. Optical microscopy, SEM, TEM, and EDX analysis were used to investigate the microstructures and deformation mechanisms and to obtain information about non-metallic inclusion particles. SiO2, MnS, and Y2Si2O7 inclusion particles were observed. An SiO2 and Y2O3 interaction was seen to have occurred during the ball milling, which impaired the final mechanical properties. Small-angle neutron scattering experiments showed that the matrix chemistry prevented effective dissolution of the yttria. © The Author(s) 2014
- ItemModern and historical engineering components investigated by neutron diffractionon ENGIN-X(Japan Society of Mechanical Engineers, 2012-06-29) Paradowska, AM; Tremsin, A; Kelleher, JF; Zhang, SY; Paddea, S; Burca, G; James, JA; Ahmed, R; Faisal, NH; Festa, G; Andreani, C; Civita, F; Bouchard, PJ; Krockelman, W; Fitzpatrick, ME; Grazzi, FThe ENGIN-X beamline is mainly used to determine residual strains/stresses deep within the interior of bulk engineering components. It is mainly used by scientists and engineers for the development of modern engineering processes and structural integrity investigations. ENGIN-X diffraction and transmission mode can be a very useful tool to measure strain, phase transitions, texture and material composition in spatial resolution in historical or archaeological artifacts and modern materials. The complexity of the shapes and sizes of the samples measured on ENGIN-X varies significantly between experiments, and this required the development of better planning, simulation and control software, SScanSS. In this paper an overview of recent developments in strain scanning on ENGIN-X and a highlight of current scientific research are presented. © 2012 The Japan Society of Mechanical Engineers
- ItemNeutron diffraction residual strain measurements in nanostructured hydroxyapatite coatings for orthopaedic implants(Elsevir, 2011-11-01) Ahmed, R; Faisal, NH; Paradowska, AM; Fitzpatrick, ME; Khor, KAThe failure of an orthopaedic implant can be initiated by residual strain inherent to the hydroxyapatite coating (HAC). Knowledge of the through-thickness residual strain profile in the thermally sprayed hydroxyapatite coating/substrate system is therefore important in the development of a new generation of orthopaedic implants. As the coating microstructure is complex, non-destructive characterization of residual strain, e.g. using neutron diffraction, provides a useful measure of through thickness strain profile without altering the stress field. This first detailed study using a neutron diffraction technique, non-destructively evaluates the through thickness strain measurement in nanostructured hydroxyapatite plasma sprayed coatings on a titanium alloy substrate (as-sprayed, heat treated, and heat treated then soaked in simulated body fluid (SBF)). The influence of crystallographic plane orientation on the residual strain measurement is shown to indicate texturing in the coating. This texturing is expected to influence both the biological and fracture response of HA coatings. Results are discussed in terms of the influence of heat-treatment and SBF on the residual stress profile for these biomedical coatings. The results show that the through thickness residual strain in all three coatings was different for different crystallographic planes but was on average tensile. It is also concluded that the heat-treatment and simulated body fluid exposure had a significant effect on the residual strain profile in the top layers of HAC.(C) 2011 Elsevier Ltd.
- ItemWeld residual stress effects on fatigue crack growth behaviour of aluminium alloy 2024-T351(Elsevier, 2009-06) Liljedahl, CDM; Brouard, J; Zanellato, O; Lin, J; Tan, ML; Ganguly, S; Irving, PE; Fitzpatrick, ME; Zhang, X; Edwards, LThe interaction between residual stress and fatigue crack growth rate has been investigated in middle tension and compact tension specimens machined from a variable polarity plasma arc welded aluminium alloy 2024-T351 plate. The specimens were tested at three levels of applied constant stress intensity factor range. Crack closure was continuously monitored using an eddy current transducer and the residual stresses were measured with neutron diffraction. The effect of the residual stresses on the fatigue crack behaviour was modelled for both specimen geometries using two approaches: a crack closure approach where the effective stress intensity factor was computed; and a residual stress approach where the effect of the residual stresses on the stress ratio was considered. Good correlation between the experimental results and the predictions were found for the effective stress intensity factor approach at a high stress intensity factor range whereas the residual stress approach yielded good predictions at low and moderate stress intensity factor ranges. In particular, the residual stresses accelerated the fatigue crack growth rate in the middle tension specimen whereas they decelerated the growth rate in the compact tension sample, demonstrating the importance of accurately evaluating the residual stresses in welded specimens which will be used to produce damage tolerance design data. © 2009, Elsevier Ltd.