Safety of industrial or military explosives is a major focus to prevent inadvertent ignition due to accidental loading as, for example, low-velocity impact. Our aim is to understand the dissipative mechanisms at work which could heat a pressed HMX-based PBX. A test based on the Split Hopkinson Pressure Bars system is proposed to carry out a dynamic triaxial compression test. This test simultaneously associates a high strain rate and a high pressure. Data have shown almost the same friction angle as during quasi-static experiments, but a higher cohesive stress. Then, A reversed edge-on impact test has been developed. This experiment enables the real-time observation of the deformation mechanisms at the microstructural scale. No relative displacement is observed between the biggest HMX grains and the matrix made of the smallest grains, the binder and the porosity. Plasticity has been observed into some HMX grains as well as damage by microcracking. Meanwhile, a biphasic (HMX grains and matrix) numerical representation of the material microstructure has been considered. A comparison between experimental observations and simulations is used to determine the yield stress of HMX. The behavior of the matrix has been determined to account for the influence of the strain rate and of the damage. Lastly, a comparison between tests and simulations has highlighted (1) that heating should rather be located in the matrix than in the biggest HMX grains and (2) that the most likely heating mechanism is the friction of microcracks lips.
Experimental and numerical study of deformation modes of a pressed HMX-based explosive composition