Plastic deformation of helium bubble and void in aluminum under shock loading

The characteristic of microscopic plasticity associated with collapse of helium bubble and void in single-crystal aluminum under the same shock loading strength has been investigated by molecular dynamics (MD) simulations. The results show that both the helium bubble and the void collapse through the emission of shear dislocation loops, while prismatic dislocation loops are never observed in the simulations. The preferential dislocation nucleation sites are similar for the helium bubbles and the voids, but the number of dislocations emitted from the helium bubble outnumbers that from the voids, and the dislocation loops emitted from the helium bubbles move faster than that from the voids. Meanwhile, it is more difficult to emit dislocation loops from the leading side (the side which the shock hits first) of both the helium bubbles and the voids than from the trailing side. By analysing the resolved shear stress along the slip plane, we found that the internal pressure of the helium bubbles increase the resolved shear stress and make the dislocation emission from the helium bubbles much easier than from the voids. The curvature change from the leading side to the trailing side produced by the shock modifies the critical shear stress for dislocation nucleation, which explains the difference in the plasticity between the leading side and the tailing side of both the helium bubbles and the voids. The result will contribute to a better understanding of the microscopic mechanism through which irradiation damages affect the dynamic properties of metals.