RESPONSE OF EXPLOSIVES TO HYPERVELOCITY IMPACT AND SHEARING
Authors: J.P. Curtis, J.T. Mills, P.R. Lee, Department of Mathematics, University College London, London, United Kingdom, and others
Abstract: When an explosive is hit by a body at a speed of the order of km/s, a shock is transmitted into it. As the speed of the impact increases the reaction of the explosive becomes more violent. Reactions can range from no effect, to minor burning, deflagration, or deflagration to detonation transition (DDT). Detonation can have catastrophic consequences if similarly fast fragments are projected from the site of the first event to impact cased or uncased energetic materials in proximity, causing their sympathetic detonation. It is less easy to explain why detonation may also occur after impact and penetration of cased or uncased explosives under shearing conditions by rod or spigot-like objects at impact speeds of a few tens of m/s. We show how a new analytical method based upon shock physics and the critical rate of supply of energy has been applied to create a simple but very effective empirical model for the hypervelocity impact of cylinders. This model seems to capture well the correct relationship between projectile diameter and the critical speed below which detonation does not occur, and above which it does. We then discuss recent progress towards finding an analogous analytical method able to treat shear initiation. Qualitative results emerge from the analysis of an incompressible explosive, which appear to be broadly consistent with our experience of explosive events resulting from shear. Finally, potential further developments and augmentations of these ideas are discussed.