Modeling uniaxial ratchetting of magnesium alloys by a new crystal plasticity considering dislocation slipping, twinning and detwinning mechanisms

摘要

A crystal plasticity model considering dislocation slipping, twinning and detwinning mechanisms is constructed to model the uniaxial ratchetting of polycrystalline extruded magnesium (Mg) alloys. The dislocation slipping on the basal , prismatic and pyramidal slip systems in both the parent and twinned regions, the twinning on the extension twinning systems, and the detwinning, an inverse process of twinning, are considered simultaneously. Two different linear kinematic hardening rules are proposed, which characterize the evolutions of back stresses driving the twinning and detwinning processes, respectively. An explicit beta-rule is adopted to acquire the response of polycrystalline aggregates. The developed constitutive model is validated by comparing the predictions with the corresponding experiments for the uniaxial ratchetting of AZ31 Mg alloys with various stress levels, where the dislocation slipping, twinning and detwinning are activated simultaneously or individually.