Dynamics simulations of RDX-based explosive materials during impact: role of the microstructure

Abstract

The present work is a numerical investigation of the influence of different microstructural characteristics on the sensitivity to shock of energetic materials. We study three energetic materials that have the same composition in terms of weight fractions of their individual constituents (RDX and wax) but markedly different microstructures and shock sensitivity. Namely, the materials are made of grains with (i) smooth grain boundaries and intra-granular defects, (ii) sharp edges and few defects, and (iii) smooth grain boundaries and very few intra-granular defects. Making use of X-ray micro-computed tomography images of the materials, we first identify and quantify morphological differences in terms of grain size distribution, grain spatial distribution, grain shape, and contact points between grains. Second, we generate representative synthetic microstructures with realistic grain shapes and controlled morphological parameters based on the segmented images. We generate virtual granular materials in two and three dimensions, with and without pores, and with different grain shapes. Third, we carry out dynamic numerical simulations of shock wave propagation on various microstructure models. In all models, points of elevated temperature (hot spots) are observed along intra-granular defects and near contact points between grains. The histograms of the computed pressure field and temperature field (albeit to a lesser extent) show differences in the tails depending on the microstructure models representing the different materials. Numerical predictions are found to be in good agreement with experimental results: the VI-RDX-based material, which is the least sensitive to shock, has the fewest hot spots, while the RS-RDX-based and RVI-RDX-based materials have similar shock sensitivities and hot spot densities. The simulations emphasize a strong influence of intra-granular defects and contact points on the sensitivity to shock for these materials.