Méthode de couplage entre expérimentations et simulations numériques en vue de l'identification de lois de comportement intracristallin. Application aux alliages de zirconium

This thesis presents a methodology for multiscale coupling between the morphology and texture of a microstructure as has been characterised experimentally, and the results of mechanical strain field analysis. This methodology is based on a coupling between experimental characterisation of the microstructure, ex-situ mechanical tests, local strain field measurements performed at the grain scale, and finite element simulations. Then, a definition of a cost function is proposed in order to optimise the parameters of the crystallographic constitutive law. This method is applied to the studies of zirconium alloys in order to improve the understanding of their mechanical behaviour in relation with their microstructures, which is a key requirement for their use in the nuclear industrie. This work was funded by the joint research program SMIRN between EDF, CEA and CNRS.Cette thèse présente la mise en place d'une méthodologie pour un dialogue multi-échelle entre la caractérisation microstructurale, consistant en une étude de la morphologie et de la texture cristallographique du matériau, et celle des champs mécaniques associés, notamment de déformation. Cette méthode est basée sur un couplage entre la caractérisation expérimentale de la microstructure, des essais mécaniques macroscopiques, des mesures de champs de déformation déterminées à l'échelle intragranulaire, et des simulations numériques par éléments finis. Enfin une définition d'une fonction coût est proposée dans le but d'optimiser les paramètres de la loi de comportement cristallographique retenue. Cette méthode a été appliquée à l'étude des alliages de zirconium dans le but d'améliorer la compréhension de leur comportement mécanique en relation avec leur microstructure. Compréhension qui est un point clef de leur utilisation dans le domaine de l'industrie nucléaire. Cette thèse a été réalisée dans le cadre du CPR SMIRN, regroupant des laboratoires du CNRS, du CEA et d'EDF

EBSD : a major device for mechanical characterization of polycrystalline materials

This paper presents a coupling methodology between microstructure characterization, mechanical tests and numerical simulations for polycrystalline materials that has been developed in order to compare directly and simultaneously numerical results to experimental ones at different length scales. This methodology is based on Orientation Imaging Microscopy that is used to obtain a crystallographic orientations field (X, Y, & & &) of the zone of interest of the polycrystalline sample. Then these data can be analyzed to yield statistical information about the microstructure as the size of the Representative Volume Element, based on texture analysis, and also about the location of grain boundaries that is used to generate automatically a Finite Element mesh from a subsection of this investigated microstructure. Secondly, Digital Imaging Correlation technique, performed during mechanical test, is used to characterize the in plane strain field associated with the microstructure. This field quantifies the local in-plane strain heterogeneities and their spatial distribution with respect to the microstructure. From this intragranular in-plane field, different kinds of averages can be obtained as grain averages, phase averages (where a phase could be defined as the sum of grains with the same crystallographic orientation) and of course the macroscopic strain. Finally, a Finite Element simulation can be carried out on the mesh that was generated. This FE simulation uses crystallographic constitutive laws and the grain orientations as measured thanks to EBSD. The in-plane experimental displacements obtained by the DIC technique are then applied as boundary conditions at the mesh edges. This allows a comparison of the intragranular strain or displacement fields in the whole mesh without artefacts generated by homogeneous or periodic boundary conditions, as is typically the case in conventional approaches

3D simulations of microstructure and comparison with experimental microstructure coming from O.I.M analysis

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