Constitutive modeling of multiscale polycrystals considering grain structures and orientations

Abstract

Traditional macro-scaled plasticity theories may not be fully valid and accurate in study of meso-/micro-scaled deformation due to the existence of size effects (SEs). In meso/microforming, there are only several to ten grains in the deformation zone. The anisotropy of individual grains significantly affects the mechanical responses and deformation behaviors of polycrystalline metallic materials. Meanwhile, grain boundaries are isotropic and generally considered as barriers to plastic deformation. In this research, the constitutive modeling considering the orientation and boundary-interior difference of grains was developed and validated by the SE-based experiments and simulations with different specimens and grain sizes. In compression tests, discontinuous shear bands are found to be generated with a zig-zag distribution in the coarse-grained specimen, but long and continuous shear bands appear in the fine-grained specimen. In tensile and meso-heading tests, microcracks initiate at grain boundary regions and grow along grain boundaries. More and smaller microcracks exist in the fine-grained material, while coarse grains facilitate the formation of larger cracks. Furthermore, compared with the crystal plasticity simulation, the simulation using the proposed modeling loses a little accuracy in prediction of freeform geometry in compression but has the advantages of high simulation efficiency and accurate prediction of flow stress. This modeling is thus suitable for addressing the meso-/micro-scaled engineering deformation problems of polycrystalline materials.