Spall fracture in aluminum monocrystals: a dislocation-dynamics approach

Abstract

High-purity monocrystalline aluminum disks of three crystallographic orientations were subjected to carefully controlled planar impact producing low levels of spall damage. This damage was observed by optical and scanning electron microscopy of sections through the recovered disks, and was found to consist of voids of essentially octahedral form having {111} planes as faces. To describe the growth of these voids we propose a kinematical model based on the motion of edge dislocations. Dynamical equations describing the rate of growth of an individual void are obtained by applying established concepts of dislocation mechanics to the kinematical model. Finally, the dynamical void growth model is combined with an empirically established nucleation model to yield equations for calculating the total volume growth rate in a spalling sample. Extension of these results to other ductile fracture phenomena is suggested.

HotQC simulation of nanovoid growth under tension in copper

“…8. This finding is in keeping with observations of void evolution in FCC metals during spall experiments (Stevens et al 1972). …”

Molecular dynamics modeling and simulation of void growth in two dimensions

“…Further dislocation nucleation events lead to the formation of kinks and the initial stepped perimeter (with atomic steps) of the circular void is transformed into a polygonal perimeter with ledges (multiple atomic steps), as shown in figure 3. It should be noted that stepped surfaces have been reported as preferential sites for dislocation nucleation during nanoindentation of gold surfaces and the results were confirmed by atomistic simulations [47,48], In addition, void growth by heterogeneous nucleation of dislocations at the void surface has been observed experimentally under very high strain rate deformation [4,5], For the sake of comparison, the dislocation nucleation in the cylindrical void simulated in 3D is shown in figure 3(d). Dislocation nucleation in 3D occurs by the formation of a loop, instead of a straight dislocation.…”

“…The typical size of the voids found in metallic materials encompasses various orders of magnitude, from nm (as those associated with He bubbles created by neutron irradiation [1]) to [xm (as those nucleated by the fracture or decohesion of brittle inclusions [2]) and the physical mechanisms of void growth depend on the size. For nm-sized voids, there is experimental evidence that void growth occurs by the emission of shear dislocation loops from the void surface, which evolve by cross slip to prismatic loops, leading to an increase in the void dimensions [3][4][5][6][7], The critical stress to generate dislocation loops from the void surface is, however, very high and this mechanism is restricted to very high strain rates or low temperatures [8],…”

Growth and collapse of nanovoids in tantalum monocrystals

“…Stevens et al [7] proposed a dislocation-based model for growth of voids, in which the void is a sink of dislocations. In the model proposed by Meyers and Aimone [8], intersecting dislocations diverging from a point were considered.…”