Localized deformation modes and non-Schmid effects in crystalline solids .2. Deformation patterns

A rate-dependent multiple slip model incorporating non-Schmid effects and thermal deformation, developed by Dao and Asaro (1993), is implemented into finite element codes to study deformation patterns before and after the shear band initiation in single crystals. Simulations using different hardening rates and different non-Schmid effects show that non-Schmid effects provide a consistent explanation for the formation of coarse slip bands (CSB), and that high hardening rates, typical of single crystals, can cause localization to not persist. Serrated flow is found accompanying the development of CSB's even with significant strain hardening. Elastic anisotropy has important influences on the onset of shear bands that form in single slip. Whether macroscopic shear bands (MSB) form first on directions that are close to what would be the primary slip plane or conjugate slip plane in a single crystal test, depends on the slip system geometry with respect to the loading orientation and the hardening function (self hardening and latent hardening). The transition from coarse slip bands to macroscopic shear bands is simulated and analyzed in detail, showing the importance of non-Schmid effects and the hardening function. Geometric effects, especially non-uniform lattice rotations, play important roles in the formation of both coarse slip bands and macroscopic shear bands. Consistency between the calculations and the theory predictions of the critical conditions of localization in Part I of this series (Dao and Asaro, 1996) as well as the existing experimental evidences are found.