Étude multi-échelle des mécanismes de déformation ductile de polycristaux synthétiques de chlorure de sodium.

Abstract : There is a renewed interest in the study of the rheology of halite since salt cavities are considered for waste repositories or energy storage. This research benefits from the development of observation techniques at the micro-scale which allow precise characterizations of microstructures, deformation mechanisms and strain fields. A procedure to make synthetic halite samples of different grains sizes has been devised. Macroscopic tests have been made to compare the behavior of synthetic samples with the one of natural salt. Uniaxial compression tests have been performed with a conventional press and with a specific rig fitted inside a scanning electron microscope. Digital images of the surface of the sample have been recorded at several loading stages. Surface markers allow the measure of displacements by means of Digital Image Correlation (DIC) techniques. Global and local strain fields are then computed using DIC and ad hoc data processing. Analysis of these results provides a measure of heterogeneity at various scales, an estimate of the size of the representative volume element and most importantly an identification of the deformation mechanisms, namely crystal slip plasticity (CSP) and grain boundary sliding (GBS) which are shown to be in a complex local interaction. The applied macroscopic loadings give rise locally to complex stress states owing to relative crystallographic orientations, density and orientation of interfaces, local deformation history. We have quantitatively estimated the relative importance of CSP and GBS for different microstructures and evidenced a marked grain size effect. We have also done some finite element simulations based on crystal plasticity which are in good agreement with the experimental results in terms of identification of active slip systems. Finally some 3D experimental developments using Xray tomography and preliminary results are shown.
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Mathieu Bourcier. Étude multi-échelle des mécanismes de déformation ductile de polycristaux synthétiques de chlorure de sodium.. Mécanique des solides [physics.class-ph]. Ecole Polytechnique X, 2012. Français. ⟨tel-00841209⟩

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