| The objective of this research is to develop an understanding of the mechanical behavior and dislocation microstructure evolution of copper single and polycrystals, and to delineate the physical and mechanical origins of spatially-localized plastic deformation. Traditional approaches to the study of plastic instabilities have either been based on kinematic considerations, such as finite strain effects and geometric softening, or physics-based concepts. In this study, we develop a framework that combines both approaches. A rate-independent crystal plasticity model was developed to incorporate micromechanics, crystallinity and microstructure into a continuum description of finite strain plasticity. A comprehensive dislocation density model based on rate theory is employed to determine the strain hardening behavior within each plastic slip system for the fcc crystal structure. Finite strain effects and the kinematics of crystal plasticity are coupled with the dislocation-density based model via the hardening matrix in crystal plasticity.;ABAQUS/CAE is employed as a finite element method solver, and several user's subroutines were developed to model fcc crystals with 2 and 12 slip systems. The developed material models are applied to study single and polycrystal deformation behavior of copper. Interfaces between the ABAQUS user's subroutine Umat and the ABAQUS main code are developed to allow further extension of the current method.;The results of the model are first compared to earlier simulations of localized shear bands in a single copper crystal showing the association of the shear band with defects, as illustrated by Asaro. Current simulations for bicrystals indicate that shear band localization initiates at the triple point junction between the two crystals and the free surface. Simulations carried out for polycrystals clearly illustrate the heterogeneous nature of plastic strain, and the corresponding spatial heterogeneity of the mobile dislocation density. The origins of the spatial heterogeneities are essentially geometric, as a result of constraints on grain rotation (finite strain effects), geometric softening due to plastic, unloading of neighboring crystals. The physical origins of plastic instabilities manifest themselves in the coupling between the dislocation densities and the localized kinematically-induced softening. |
