Enhancement of metal surface micro-jet by nanoscale helium bubbles under supported and unsupported shocks

By using molecular dynamics, we have investigated the effect of nanoscale helium (He) bubbles on the formation of micro-jets and the various physical mechanisms under supported and unsupported shock wave loading. Our simulations suggest that the micro-jet is primarily influenced by the local dynamics of the nano-He bubbles, as the velocity of the shock wave in copper-helium (Cu-He) system is slightly slower than in pure Cu. The expansion of He bubbles can accelerate the velocity of the jet head, but this effect disappears during the released tensile stage. We categorize the behavior of nano-He bubbles into three types: Type A bubbles are in the micro-jet forming region, and their expansion increases the velocity and rupture of the jet. Type B bubbles are located between the micro-jets, and their compression and rapid bursting accelerate the free surface. Type C bubbles are situated far from the free surface and mainly affect the propagation of the shock wave and the released damage process. The global effects of the He bubble are similar under both supported and unsupported shock wave loading. However, the evolution of Type C He bubbles is significantly different under unsupported shock wave loading, with pressure-atom volume and density attenuated to zero and temperature reduced to the initial temperature due to the strong tensile effect. Overall, our study has revealed the differences in the evolution process of He bubbles and their dynamic effects during the formation of micro-jets under different compressed and released paths.