Numerical and experimental study of the plasticity of HMX during a reverse edge-on impact test

Abstract

The initiation mechanisms of mechanically stressed explosive compositions are largely dependent on the behaviour of the constituents, and the formation of hot spots is linked to the location of anelastic strains. This study takes a first step towards understanding the behaviour of HMX crystals (cyclotetramethylenetetranitramine, C4H8N8O8, octogen) when these are subjected to quasi-static stress. Our analysis couples the numerical simulation of the composite material at the mesoscopic scale with observations made at this same scale during weakly confined quasi-static tests. For the simulation, we have chosen a biphasic description of the composite by separating the large particles from the matrix otherwise assumed to be homogeneous. The matrix is, in fact, composed of smaller particles, binder and porosities. The behaviour of the HMX particles is determined from data in the literature: this opens up three possibilities with respect to its plastic behaviour. Based on triaxial tests and given the macroscopic response of the composite, the behaviour of the matrix is identified for each possibility with regard to the behaviour of the HMX particles. Real time observations made at a mesostructural scale firstly enable the plastification of the HMX particles to be demonstrated and secondly, by comparison with numerical simulations, enable a model to be attributed to these particles.