Scale dependence of thermal hardening of fcc metals under shock loading

Abstract

A dislocation-based constitutive model is applied to revisit the anomalous thermal hardening behavior of fcc metals under shock loading. Two scale-dependent dislocation motion mechanisms are found to dominate the thermal hardening behavior of fcc metals under shock loading. In particular, because of the shear stress decay with the propagation of the shock wave, the relativistic effect of dislocation motion is only significant near the impact surface, whereas the phonon drag mechanism dominates dislocation motion in a macroscopic fcc metal. Furthermore, we provide a detailed picture of the thermal hardening behavior on the continuum scale, in which the role of the newly generated stress wave from plastic deformation in the dynamic deformation process is highlighted. We show that the mechanical response at the elastic precursor is mainly controlled by the stress wave emanating from the plastic front.