Near CJ shock initiation of PBX 9502: modeling and experiments

The shock-to-detonation transition characteristics of the high explosive (HE) PBX 9502 are experimentally and computationally explored in extremely high input pressure conditions. 

The experiments were designed to respond to the subtle differences in two continuum detonation performance models typically employed to predict the initiation response of PBX 9502. The employed model variants mostly differ in their definition of the reaction rate functional form and flow variable dependencies. The present experiments provide a novel platform to evaluate the quantitative and qualitative consequences of utilizing a shock-pressure based versus a shock-temperature based reactive flow model in initiation conditions beyond the range of calibration of either model. In this case we investigate the region around the PBX 9502 CJ pressure, ~28 GPa.

 

The experiments capture the extremely fast transient build-up of shock-induced reaction via optical measurements of the interface particle velocity between the HE samples and PMMA windows. The necessarily thin HE samples were polished to thicknesses ranging from 0.2 to 3.5 mm. For each experiment, up to eight samples were mounted onto copper baseplates. Projectiles with 5 mm thick copper impactors were launched at velocities of 2.5 and 3.0 km/s, resulting in impact pressures of 25 and 31 GPa and run distances to detonation of 0.3 and 1 mm respectively. Multiple experiments were fired at the same impact conditions to allow the development of a highly diagnosed set of wave-profiles detailing the growth to detonation over these very short distances and time intervals; the sub-CJ experiment (25 GPa) resulted in a montage of twenty-five wave-profiles. These experiments provide evidence of reactive evolution in very high-pressure states along with evidence of reactive growth in an overdriven state. This new information adds to an improved physics understanding and will inform further model development for this well studied explosive.