Explosive Impulse Response Two-dimensional Micro-discrete Element Simulation

Mesoscopic structures significantly affect the shock response of explosives. Presently this problem is mostly investigated through grain scale numerical simulations. In this thesis, the discrete element method has been used to simulate the formation and development of hot spots in shock loaded granular and plastic bonded explosives.The geometrical part of the discrete element model that mimics the mesoscopic structure of explosives was created based on the Voronoi tessellation. Correspondingly, the discrete element code DM2 was modified to satisfy the special needs of this study. Improvements were also made on the original normal force model. That is, the central force was replaced by a modified Hugoniot relation, and the artificial damping was replaced by the physical volumetric viscosity. In addition, the idea of representative volume element has been used to redefine both the volumetric and the shear strains.Based on the above efforts, two dimensional mesoscale discrete element simulation of shock response of explosives has been performed. Reasonable results were obtained by using the physical parameters from the literature. The temperature scale of hot spots is comparable to that in other works. In this study, viscoplastic deformation is the main cause for temperature localization, whereas the effects of friction and volumetric viscosity are very small. By comparing the granular and the plastic bonded explosives, it was found that the cushioning effect of the binder can reduce the temperatures of hot spots. Simulations of explosives of different shapes impacting on a rigid wall showed that the loading method and boundary condition affected the temperatures of hot spots more than affecting their spatial distribution. For explosive sample with a void inside, it was found that void collapse can significantly raise the local temperature. The reason for this is the severe viscoplastic deformation in materials surrounding the void due to loading, unloading, and reloading of the stress wave.