Non-equilibrium molecular dynamics simulations of the spallation in Ni: Effect of vacancies

The effects of defects on the fracture resistance of materials have attracted considerable attention recently. In the present work, the vacancy effects on the spallation in single-crystalline Ni are studied by nonequilibrium molecular dynamics simulations. The vacancy concentration ranges from 0% to 2.0%, and the spallation in shock wave loading along three low-index directions ([0 0 1], [1 1 0], and [1 1 1]) is investigated. We found that vacancies provide the sites of nucleation for compression-induce plasticity, and tension stress-induced plasticity plays the key role in void nucleation. Along the [0 0 1] direction, the degree of spall damage does not increase with the increase in vacancy concentration; however, along the [1 1 0] and [1 1 1] directions, it decreases with the increase in vacancy concentration when the vacancy concentration is higher than the threshold value.