Deformation twinning at aluminum crack tips

Recent experimental evidence has shown that even fcc materials that are not normally associated with deformation twinning, such as aluminum, will twin given a sufficiently high stress concentration such as at a crack tip. In this paper we present a computational study of the atomic structures that form at the tips of atomically sharp cracks in aluminum single crystals under loading. The simulations were carried out using the quasicontinuum method - a mixed continuum and atomistic approach. A variety of loading modes and orientations were examined. It was found that for certain combinations of loading mode and orientation, deformation twinning does occur at aluminum crack tips in agreement with experimental observation. For other configurations, either dislocation emission or in one case the formation of an intrinsic-extrinsic fault pair was observed. It was also found that the response at the crack tip can depend on the crack-tip morphology in addition to the applied loading and crystallographic orientation.