Computational Examination of Deformation Wave-boundary Interaction for Granular Explosive

Experiments have shown that the interaction of deformation waves propagating through heterogeneous energetic solids with confining boundaries can result in combustion of these materials. Wilson, et al. [1], observed ignition at an anvil-explosive interface while loading an explosive with shock levels below the plane shock initiation threshold. These observations are of practical significance since most explosive hazards and accident scenarios involve inadvertent loading of the material and complex waveboundary interactions. Though the loading of granular explosives by planar deformation waves has been studied extensively, the analysis of complex wave-boundary interactions has received comparatively little attention. To this end, we numerically investigate the interaction of an initially planar deformation wave with a curved boundary. The bulk hydrodynamic compaction model studied here is based on a continuum mixture theory and accounts for energy dissipation due to volumetric deformation [2]. Material properties chosen for the study are representative of the well characterized granular high explosive HMX (C4H8N8O8). Figure 1: Schematic of the domain and Boundary Conditions (BCs) used in the numerical study. The model problem is depicted in Fig. 1. A planar incident wave travels through the domain from left to right and collides with the rigid anvil surface. The wave is initialized in the domain by using spatial variation of density, pressure, velocity, and volume fraction, obtained from the solution of the steady state form of the governing equations in one dimension. Boundary conditions imposed are indicated in the figure. Unnecessary computational effort has been avoided by taking advantage of the symmetry of the problem. The hyperbolic system of governing equations is solved using a Total Variation Diminishing (TVD) high-resolution shock capturing method formulated by Kurganov and Tadmor [3]. The numerical code used in the study has been verified with standard gas dynamics problems and steady solutions for hydrodynamic compaction waves. Representative predictions are given here for a particular case where the initial solid volume fraction of Figure 2: Contours of the (a) solid pressure and the (b) grain scale heat flux at t = 4.85 μs.