Shock response of pre-existing spall damage in copper

We perform molecular dynamics simulations to investigate second-shock-induced recompaction and the subsequent re-spallation process in Cu with pre-existing spall damage. Compared with the conventional spalling of pristine Cu free of damage, a clear disturbance is observed in the free-surface velocity under the second shock of a pre-spalled Cu sample. This is due to the complex interactions of shock waves during the collapse of existing voids. Full recompaction accompanied by local melting of residual damage is also observed in our second-shock simulations. Secondary spallation occurs after the recompaction process, and the effect of secondary loading conditions, including different values of the peak shock pressure and different flat-top widths of the shock wave, on second spallation is taken into account. The findings clearly show that the spall strength of pre-spalled Cu is lower than that of pristine Cu under the same loading conditions when the loading time is sufficiently long. This result is evidence of the locally disordered state of the recovered sample. Re-solidification accompanied by atomic rearrangement is observed in the disordered region after second-shock compression.