High-velocity Impact Fragmentation of Brittle, Granular Aluminum Spheres

We present ballistic and fragmentation data for brittle, granular aluminum spheres following high- velocity impact (0.5-2.0 km/s) on thin steel plates. These spheres, formed from isostatically pressed alu- minum powder, are representative of a wide variety of metallic reactive materials currently being studied. Simple analytic theories are introduced which provide a reasonable description of the residual velocity and hole diameter following impact. With increasing velocity there is an intriguing transition to a power-law fragment distribution, which we have interpreted as arising from extensive microbranching of fast-running cracks. The key equations of an analytic theory describing the fragment distributions are also presented.