Dynamic fracture characteristics of nanocrystalline Al containing He bubbles

This Letter reports the individual and combined effects of He bubbles and grain boundaries on the spallation of aluminum at different strain rates. Molecular dynamics simulations show that both He bubbles and grain boundaries reduce the spall strength, with the effect of He bubbles being reduced by about 50% when a grain boundary is present. Furthermore, it is found that He bubbles inhibit void nucleation and growth, while grain boundaries determine the location and mechanism of void or He bubble nucleation and growth, leading to a more rapid reduction in the spall strength of polycrystals than single crystals as the strain rate decreases. Additionally, a linear relationship is found between the spall strength of polycrystalline Al and the fraction of He atoms when He concentration is below 0.4 at.%.