A dislocation-based constitutive description of strain-rate effect on the deformation resistance of metals

A dislocation-based model is presented to study the strain-rate effect on the deformation resistance of metals over a wide range of strain rates. The model is able to take into account the multi-mechanisms, such as dislocation generation, viscous drag, and thermal activation. The results reveal that at high temperatures, the mechanism of viscous drag may play a more significant role than the thermal activation mechanism; whereas at lower temperatures, the viscous drag may be important only under high strain-rate loadings. The cause of deformation instability is also probed. At small plastic strains, deformation instability may be induced by the decrease of the thermally activated stress with increasing deformation. When plastic strains are large, the decreasing of the resistance for dislocation generation with increasing deformation may be the cause.