Modeling of shock-induced plasticity of single-crystalline magnesium with a coupled dislocation and twinning constitutive model

Despite significant attention over recent decades, the dynamic plasticity of magnesium (Mg) under high pressure and high strain rates remains far from well understood owing to the complexity of deformation under such extreme conditions. In particular, dynamic twinning plasticity is still described by phenomenological models, which limits further understanding of the dynamic mechanical response of metals. In this work, a twinning substructure model, in which twinning nucleation, propagation, and growth are taken into account, is applied to address plastic deformation of single-crystalline Mg subjected to shock compression. The model is coupled with a dislocation plasticity model under the thermoelastic-viscoplastic framework. By utilizing this combined model, a quantitative connection between the evolution of defects, including dislocations and twins, and the experimentally measured wave profiles is established. Modeling the mechanical response of single-crystalline Mg under shock compression provides new insights into the twinning-related plasticity of Mg, revealing that the typical features of the wave profile of Mg are significantly influenced by twinning, especially those along the (10-10) direction. Notably, in contrast to the classical understanding predicted by the dislocation plasticity model that deformation on the elastic precursor wavefront is purely one-dimensional elastic, the new model indicates that twinning nucleation leads to considerable plastic deformation on the elastic precursor wavefront. Additionally, plasticity along the (10-10) direction at the plastic front is demonstrated to be governed by twinning and dislocation mechanisms acting together, while the power-scaling law appears to be almost independent of the twinning mechanisms.