Shock initiation sensitivity studies of low-density pressed and thermally damaged polymer bonded explosive (PBX) 9501

Understanding the initiation sensitivity of high explosives that have been damaged through mechanical or thermal insults is important to safely handling the material. The shock initiation sensitivity of polymer bonded explosive (PBX) 9501 has been extensively studied at ambient and non-ambient temperatures. However, changes in morphology that result from inefficient pressing of the material or applied heat to the high explosive have not been explored for PBX 9501. PBX 9501 was purposely pressed at low densities, resulting in initial densities of 1.81 and 1.50 g/cm3. The resultant morphology of the low-density pressed PBX 9501 was spherical-like voids. PBX 9501 was also thermally damaged by heating to 120, 150, and 170 °C, resulting in initial densities of 1.77, 1.73, and 1.56 g/cm3, respectfully. This method resulted in fractal-like damage to the material. We tested the shock initiation sensitivity by performing gas gun driven planar impact experiments with embedded electromagnetic gauges that allow for both the calculation of the input pressure, along with the direct measurement of the shock-to-detonation transition. At initial densities around ∼1.8 g/cm3, more similar to the initial pressing density of PBX 9501 at 1.83 g/cm3, both materials showed an increase in sensitivity with shorter shock-to-detonation transitions than pristine PBX 9501. It appears that the spherical-like voids resulted in the more sensitive high explosive. The lowest initial densities, ∼1.5 g/cm3, showed a significant shift in the shock-to-detonation distances. It appears that the two morphologies at these lower initial densities resulted in similar initiation sensitivities.