Void growth by dislocation emission

Laser shock experiments conducted at an energy density of 61 MJ/m revealed void initiation and growth at stress application times of approximately 10 ns. It is shown that void growth cannot be accomplished by vacancy diffusion under these conditions, even taking into account shock heating. An alternative, dislocation-emission-based mechanism, is proposed for void growth. The shear stresses are highest at 45 to the void surface and decay with increasing distance from the surface. Two mechanisms accounting for the generation of geometrically necessary dislocations required for void growth are proposed: prismatic and shear loops. A criterion for the emission of a dislocation from the surface of a void under remote tension is formulated, analogous to Rice and Thomson s criterion for crack blunting by dislocation emission from the crack tip. The critical stress is calculated for the emission of a single dislocation and a dislocation pair for any size of initial void. It is shown that the critical stress for dislocation emission decreases with increasing void size. Dislocations with a wider core are more easily emitted than dislocations with a narrow core. 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.