EBSD : a major device for mechanical characterization of polycrystalline materials
Résumé
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.