Characterizing the propensity of hypervelocity metal fragments to initiate plastic bonded explosives

The off-normal detonation behavior of two plastic-bonded explosive (PBX) formulations was studied using explosively-driven aluminum fragments created by two types of detonators. A generic aluminum-cupped detonator contained 100 mg of PETN which was sufficient to fragment the aluminum into hundreds of sub-mm particles moving at hypersonic velocity; for comparison, a Teledyne RISI® RP-80 was also tested which generated a more substantial flyer plate of aluminum. Low-density polystyrene foam was used as a witness material with subsequent computed tomography analysis to characterize the distribution of particles post-test. Precise digital in-line holography experiments were conducted in situ to measure three-dimensional shape and size of the fastest-moving fragments as they impacted PBXs. Fragments showed significant variability in size, shape and distribution or clustering. Depending on the shot, single or multiple shock impacts could be imparted to the PBX from the generic detonator fragments, or clusters, ranging in size between 100 and 1100 microns and velocities up to 3.5 km/s. The generic detonator fragments were sufficient to initiate PBX 9407 up to 115 mm away, but PBX 9501 was only initiable up to 6 mm. When an RP-80 detonator was used, the more substantial flyer plate initiated PBX 9407 up to 457 mm, while PBX 9501 was only initiable up to 149 mm. This type of data is critical for safety experiments and enables comparison between detonators with different fragment patterns.