Hot Spot Formation in Mock Materials in Impact Sensitivity Testing by Drop Hammer

Powder and granulated sugars were exposed to the drop hammer impact test configured with 120- and 180-grit Si/C sandpapers. The sugars were selected as mock materials for HMX (Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine). The drop heights ranged from 24.2 to 40.7 cm. Samples were examined by visible microscopy before and after testing and the appearance of yellow and brown discolorations in the spent samples were assigned as hot spots. These discolorations were divided into two types; those collocated with grit particles and those that were not. Hot spots are found in the spent samples in almost every test condition. Powder sugar appears to be more active in producing hot spots than the granulated sugar based on comparisons at identical conditions. Drop height, within this specific range, has little effect on the formation of hot spots, except for 40.7 cm high-end limit, which causes a dramatic increase in spot formation. The predominant hot spot type formed is collocated with grit particles, suggesting association of hot spot formation due to grit, something that has been discussed in previous treaties. Foreign objects were also observed, some imbedded and some not imbedded. Discoloration was not observed around these sites, suggesting these types of foreign materials are not responsible for hot spot formation, at least under these conditions. Grit associated with a visible tail was observed in some instances, suggesting that grit can be quite mobile through the sample when the pressure is applied by the drop weight (through the striker).