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 impleme nted into finite element codes to study deformation patterns before an d after the shear band initiation in single crystals. Simulations usin g 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 o nset of shear bands that form in single slip. Whether macroscopic shea r 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 te st, depends on the slip system geometry with respect to the loading or ientation and the hardening function (self hardening and latent harden ing). The transition from coarse slip bands to macroscopic shear bands is simulated and analyzed in detail, showing the importance of non-Sc hmid 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 bet ween the calculations and the theory predictions of the critical condi tions of localization in Part I of this series (Dao and Asaro, 1996) a s well as the existing experimental evidences are found.