Evolution of perturbations of temperature and dislocation density at high-rate shear deformation of pure metals and alloys

We have investigated numerically an evolution of initial perturbations of temperature or dislocation density in metals at high-rate deformation and its influence on the localization of plastic flow. A high-rate simple shear of micro-samples of pure metals and alloys, coarse-grained as well as nano-crystalline, has been simulated in two-dimensional geometry with use of the continuum mechanics supplemented by the dislocation plasticity and the grain-boundary sliding models. Perturbations of the temperature or dislocation density lead to restricted localization of the plastic deformation, but they can not initiate instability of the plastic flow as a self-sustained and increasing process. A more effective reason of the localization is the stress concentration, caused, for example, by boundary conditions. Rate of the plastic deformation is maximal in areas of the shear stress localization and it can be close to zero outside these areas. Heterogeneity of the grain sizes distribution through the sample can also lead to substantial localization of the plastic flow due to the grain size dependence of the dynamic yield strength.