Experimental results from spall tests on Al revealed the presence of a dense dislocation structure in an annulus around a void that grew under the tensile pulse when a shock wave was reflected at the free surface of the specimen. The proposition was that dislocation emission from the void surface under load was a viable mechanism for void growth. To understand void growth in the absence of diffusive effects, the interstitial-loop emission mechanism under tensile hydrostatic stress was investigated. First, the micromechanics of pile-up formation when interstitial loops were emitted from a void under applied macroscopic loading was reviewed. Demand for surface energy expenditure upon void-surface change was taken into consideration. It was demonstrated that in face-centred cubic metals loop emission from voids with a radius of ~10nm was indeed energetically possible in the hydrostatic stress environment generated by shock loading. On the other hand, the levels of hydrostatic stress prevalent in common structural applications were not sufficient to drive loops at equilibrium positions above a ~10 nm void. However, for voids larger than about 100nm, the energetics of loop emission were easily met as a necessary condition even under the low stress environment prevalent in structural applications.

Void Growth by Dislocation-Loop Emission. D.C.Ahn, P.Sofronis, M.Kumar, J.Belak, R.Minich: Journal of Applied Physics, 2007, 101[6], 063514