Effect of plastic incompatibility on non-linear deformation mechanism during unloading in HCP crystals

Abstract

In polycrystalline materials with strong plastic anisotropy such as HCP metals, significant nonlinear deformation during unloading is frequently observed. One possible mechanism for nonlinear unloading behavior is activation of slip system with the help of the internal stress which is developed during preloading. As an effective internal stress for nonlinear unloading behavior, a number of researcher have pointed out the effect of the intergranular stress which is induced by difference in flow stress for each grain. Alternatively, in polycrystals, significantly non-uniform stress field within each grain could be developed during plastic deformation because of plastic incompatibility between neighboring grains. While this non-uniform stress field would contribute to non-linear unloading behavior, the influence of non-uniform stress field on non-linear unloading behavior is not easily estimated by experiments. In this study, we numerically investigate the effect of non-uniform stress field induced by plastic incompatibility on non-linear unloading behavior in HCP crystals by a crystal plasticity finite element method.