Browsing by Author "Braham, C"

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    Elastoplastic deformation and damage process in duplex steel studied using synchrotron and neutron diffraction
    (Scientific.Net, 2017-08-22) Zhao, YC; Joncour, LL; Baczmański, A; François, M; Wroński, S; Panicaud, B; Gadalińska, E; Braham, C; Buslaps, T; Paradowska, AM
    In the present work, the mechanical behavior of phases in duplex steel during tensile test was studied. Special interest was taken in the analysis of damage process just before failure. In this aim two diffraction methods: in-situ time of flight neutron diffraction and X-ray synchrotron diffraction were applied. Using diffraction data, the slip mechanism on crystallographic planes during plastic deformation was investigated. In the case of aged UR45N steel, it was found that significant softening caused by damage process was initiated in the ferritic phase. The lattice strains measured in situ by two above mentioned diffraction methods were compared with prediction of the self-consistent model. © 2021 by Trans Tech Publications Ltd.
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    The influence of constitutive material models on accumulated plastic strain in finite element weld analyses
    (Elsevier, 2015-09-01) Muránsky, O; Hamelin, CJ; Patel, VI; Braham, C
    Recent studies in computational weld mechanics have revealed the importance of the material plasticity model when predicting weld residual stresses. The present work seeks to extend this level of understanding to include the effects of the assumed material annealing behaviour, particularly when modelling multi-pass welds that comprise several thermo-mechanical loading cycles. A series of numerical analyses are performed to examine the variability in predicted residual stress profiles for different material models, using a validated finite element model for a three-pass slot weld in AISI 316LN austenitic steel. The material models consider both the work hardening and annealing assumptions for the chosen material. Model sensitivity is established not only from a weld residual stress perspective, but also from an assessment of the post-weld plastic strain accumulated in the weldment. Predictions are compared with indirect measurements acquired using cross-weld micro-hardness maps taken from benchmark specimens. Sensitivity studies reveal that the choice of annealing behaviour will have a significant impact on plastic flow predictions, which is dependent on the annealing temperature specified. Annealing assumptions will have a varying impact on the weld residual stress predictions, such that the extent of sensitivity is dependent on the plasticity model chosen. In contrast, the choice of plasticity model will have a significant effect on the predicted weld residual stresses, but relatively little effect on predictions of equivalent plastic strain. © 2015 Elsevier Ltd.
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    Neutron time-of-flight diffraction used to study aged duplex stainless steel at small and large deformation until sample fracture
    (Wiley Blackwell, 2011-10-01) Baczmański, A; Le Joncour, L; Panicaud, B; François, M; Braham, C; Paradowska, AM; Wronski, S; Amara, S; Chiron, R
    Owing to its selectivity, diffraction is a powerful tool for analysing the mechanical behaviour of polycrystalline materials at the mesoscale (phase and/or grain scale). In situ neutron diffraction during tensile tests and elastoplastic self-consistent modelling were used to study slip phenomena occurring on crystallographic planes at small and large deformation. The critical resolved shear stresses in both phases of duplex stainless steel were found for samples subjected to different thermal treatments. The evolution of grain loading was also determined by showing the large differences between stress concentration for grains in ferritic and austenitic phases. It was found that, for small loads applied to the sample, linear elastic deformation occurs in both phases. When the load increases, austenite starts to deform plastically, while ferrite remains in the elastic range. Finally, both phases undergo plastic deformation until sample fracture. By using an original calibration of diffraction data, the range of the study was extended to large sample deformation. As a result, mechanical effects that can be attributed to damage processes initiated in ferrite were observed. © 2011, Wiley-Blackwell.
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    Study of stress localisation in polycrystalline grains using self-consistent modelling and neutron diffraction
    (Taylor & Francis Ltd, 2012-05-14) Baczmański, A; Gaj, A; Le Joncour, L; Wroński, S; François, M; Panicaud, B; Braham, C; Paradowska, AM
    The time-of-flight neutron diffraction technique and the elastoplastic self-consistent model were used to study the behaviour of single and multi-phase materials. Critical resolved shear stresses and hardening parameters in austenitic and austenitic?ferritic steels were found by analysing the evolution of the lattice strains measured during tensile tests. Special attention was paid to the changes of the grain stresses occurring due to transition from elastic to plastic deformation. Using a new method of data analysis, the variation of the stress localisation tensor as a function of macrostress was measured. The experimental results were successfully compared with model predictions for both phases of the duplex steel and also for the austenitic sample. © 2012, Taylor & Francis Group, an Informa Business.
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    Study of stresses in texture components using neutron diffraction
    (Trans Tech Publications, 2013-09-01) Baczmański, A; Gadalińska, E; Wroński, S; Joncour, LL; Panicaud, B; François, M; Braham, C; Klosek, V; Paradowska, AM
    In this work a new method for analysis of neutron diffraction results obtained during “in situ” tensile load is proposed and tested. The methodology is based on the measurements of lattice strains during “in situ” tensile test for several hkl reflections and for different orientations of the sample with respect to the scattering vector. As the result the full stress tensor for preferred texture orientations in function of applied stress can be determined with help of crystallite group method. The experimental data are presented and compared with self-consistent model calculations performed for groups of grains corresponding to the measured hkl reflections. © 2014, Trans Tech Publications.