Nanovoid deformation in aluminum under simple shear

We analyze the mechanisms underlying the deformation of a nanovoid in an Al crystal subjected to cyclic shear deformation using numerical simulations. Boundary and cell-size effects have been minimized by means of the quasicontinuum method. The deformation of the void entails a noticeable reduction in volume. During the loading phase, our analysis reveals several stages of stress buildup separated by yield points. The main mechanisms underlying the deformation of the crystal are: glide of primary and secondary partial dislocation loops with mixed edge-screw character; intersection of primary and secondary loops to form jogs and junctions; cross-slip; and dislocation multiplication and annihilation. Cross-slip occurs by the Fleischer mechanism and not by the more commonly assumed Friedel-Escaig mechanism. During unloading, most of the dislocation population and void volume reduction is recovered by re-absorption of dislocation loops and annihilation mediated by cross slip. However, a residual dislocation density remains around the void at the end of the unloading process.