Study of shock initiation in pressed energetic materials using mesoscale simulations

Pressed energetic materials have complicated microstructure and contain various forms of heterogeneities such as voids, micro-cracks, binders, energetic crystals etc. Shock interaction with the heterogeneities leads to the formation of local heated regions known as hot spots. There are different mechanisms which can lead to the formation of hot spots. However, for pressed energetic materials viscoplastic deformation of voids leading to collapse has been considered to be the most important mechanism. The reaction and specifically its growth in the pressed energetic materials depends on the temperature and location of the hot spots. Hence, an accurate representation of the microstructure is desired for mesoscale study of shock initiation. In the present work, shock initiation on pressed HMX has been studied and ignition threshold for two types of HMX materials have been established. The microstructure geometry is accurately represented using image processing algorithms employed on SEM images of both explosives. The image processing framework is incorporated in a massively parallel Eulerian code SCIMITAR3D for the mesoscale simulations. The chemical decomposition of HMX has been modeled using Henson-Smilowitz multi-step mechanism. The ignition threshold obtained for pressed HMX is compared with experimental results.