Shock compression of porous copper containing helium: Molecular dynamics simulations and theoretical model

Shock compression of porous copper containing helium is studied via non-equilibrium molecular dynamic simulations. The results show that the shock propagation exhibits an elastic-plastic double-shockwave structure at low shock velocity. The shock Hugoniot elastic limit increases with higher gas concentration, and decreases with larger porosity, while almost independent of the shock velocity. The back-and-forth propagation of elastic shockwave between plastic shockwave and free surface leads to the occurrence of the special structure of "surface cap", which can protect the porous metal in the vicinity of the free surface from collapse. The plastic shock propagates faster with higher gas concentration and gradually catches up with the elastic shockwave as shock intensity increases. Compared with porous copper without gas, the presence of helium significantly inhibits the post-shock temperature rising and the shock melting behavior. A new theoretical model was proposed to quantify the shock Hugoniot of porous materials containing gas. The model's predictions align well with MD simulations across a wide pressure range up to 100 GPa with different gas concentrations and porosities.