Effect of geometrically necessary dislocations on inelastic strain rate for torsion stress relaxation of polycrystalline copper in micro scale

To characterize the torsion stress relaxation in micro scale, the relation between the inelastic strain rate and the geometrically necessary dislocations (GNDs) is proposed. Based on the Orowan equation, which provides the description for strain rate evolution with the influence of density and velocity of mobile dislocation, the effect of GNDs is considered when materials exhibit non-uniform deformation at small scale. Additionally, the inelastic strain rate is presented as a power form of stress. Consequently, from the analysis about the test results for polycrystalline copper, the parameters for the evolution of inelastic strain rate are determined. Moreover, a time-independent plasticity model is introduced to describe the plastic hardening during the repeated stress relaxation. Finally, the activated volume from simulation and experiments are discussed in detail to interpret the underlying mechanism.