Atomistic study of shock Hugoniot in columnar nanocrystalline copper

Understanding the shock behavior of polycrystals is challenging due to the effects of grain size, defect, and orientation. In this study, we focus on the grain size and defect effects on the shock Hugoniot of polycrystals using columnar nanocrystalline copper. The dominant deformation mechanism is clarified under the impact velocities ranging from 300 m/s to 1200 m/s. The main findings from this study are as follows. The shock Hugoniot relation between pressure and specific volume has no clear dependence on the grain size, whereas the corresponding Hugoniot shear stress exhibits a grain size dependence. The primary defects of shock plasticity change from dislocation to stacking fault and finally twinning with the increase of impact velocity. As the impact velocity exceeds 1000 m/s, the shielding effect becomes prominent as a result of the defect formation on the parallel slip planes within a grain.