Spall damage in single crystal Al with helium bubbles under decaying shock loading via molecular dynamics study

The mechanism and characteristics of spall damage in single crystal Al with randomly distributed helium bubbles under decaying shock loading are studied by molecular dynamics simulations. We find that He bubble plays important role in the dynamic process. The mechanism of spall damage is dominated by He bubble expansion-merging-absorption, followed by void nucleation-growth-coalescence. During spalling process, He bubbles impede the nucleation of surrounding voids, they expand at a higher rate than that for void growth, adjacent He bubbles merge together, and small voids are absorbed by nearby large He bubble. These behaviors finally lead to a very different morphology of the damaged zone from that for the perfect crystal, whose spall damage mechanism is void nucleation-growth-coalescence. Obvious differences in temperature profile are observed between the crystal with He bubbles and the perfect crystal because the compression of surrounding atoms induced by He bubble expansion results in higher local temperature, especially in solid state. In melted state, the contribution of He bubbles becomes comparatively small since more voids are nucleated followed by faster voids growth and coalescence that lead to higher temperature rising. Additionally, He bubble significantly reduces the spall strength of Al in solid state, but this effect becomes negligible when the crystal is melted.