The problems investigated in the project fall into three broad categories: (1) Modeling of twinning under high velocity impact (2) Constitutive equations for elasto-plastic response under large deformations with application to simple shear, and (3) variational approaches to the development of governing equations and boundary conditions for incorporating lattice curvature effects in plasticity with application to shear banding problems. Results and their significance: Using a novel multiconfigurational framework developed by us, we have developed models that account for deformation twinning under high velocity impact. The results show good agreement with experimental data. We found that the nonlinearity of the elastic response will lead to interesting softening behavior when the material undergoes simple shear deformations. We have developed a theory incorporating lattice curvature effects that can effectively simulate the formation of shear bands. We have also developed a new variational technique based on the maximization of the rate of energy dissipation that not only delivers the governing differential equations but also the accompanying boundary conditions. This work will allow for the development of computational codes that can delineate the relative influence of lattice curvature, twinning and strain softening on the formation of shear bands.