On the effects of hardening models and lattice rotations in strain gradient crystal plasticity simulations

This work presents numerical simulations considering two hardening models for higher order strain gradient crystal plasticity: energetic and dissipative. These models are defined as a function of plastic slip gradients. Energetic hardening, in particular, is defined based on a quadratic uncoupled defect energy. Considering wedge indentation simulations, it is observed that the effect of the hardening models depends on the indenter angle, with the energetic hardening effect being less relevant for flatter indenters. Comparisons with discrete dislocation simulations suggest also a link between the presence of dislocation obstacles and energetic hardening. Microstructures obtained with each hardening model are different, with the dissipative case presenting a geometrically necessary dislocation distribution that exhibits some of the characteristics seen in “cell-wall” structures. Changes in the geometrically necessary dislocations with lattice rotations are also influenced by hardening definition. This work shows that these changes are important to determine the evolution of plastic slip distributions.