Mechanical Behavior of Energetic Materials During High Acceleration in An Ultracentrifuge

The mechanical behavior of explosives subjected to high acceleration (high g) has been studied in an ultracentrifuge. The experiments reported here reveal new information on the mechanical behavior of such materials and the influence of grain size on the fracture process. Through measurement and analysis of fracture surfaces, we have found that predominately intergranular failure occurs when the shear or tensile strength of the explosive is exceeded. We have found that the mechanical strength of melt-cast polycrystalline TNT varies inversely with crystal size. That is, if the sample consists of large, homogeneous crystals, these are found to separate from the sample at lower g-levels due to the larger mass-to-binding surface area ratio of the crystals. Conversely, smaller original crystallites are found to separate at higher g-levets due to the smaller mass-to-binding surface area ratio. Our results show that single crystals of TNT fracture under a higher g-level at crystal defects. We have also found that the fracture acceleration of Octol decreases with increasing percent TNT and decreasing percent HMX. Hexanitrostilbene (HNS) has been shown by other investigators to be an effective additive to prevent growth of large TNT grains. We have found that the fracture acceleration increases when HNS is added to Octol.