An evaluation of higher-order single crystal strength models for constrained thin films subjected to simple shear

An evaluation of different dislocation density-based strength models for a theory of micropolar single crystal plasticity is presented through detailed comparison with discrete dislocation dynamics simulations of a constrained thin film subjected to simple shear. The principal component of the evaluation is determining the most appropriate way to incorporate scale-dependent strengthening due to geometrically necessary dislocations (GNDs) within the model. We find that some models give results consistent with the discrete dislocation simulations, yet it is shown that models based on a generalized Taylor relation do not. Additionally, we briefly discuss the differences between models derived from unified (single) and independent (multiple) flow criteria, and demonstrate that single criterion models provide comparable predictive capability while introducing fewer nonlocal constitutive parameters.