Threshold and violence of reaction in explosives containing cavities or adjacent gaps were determined for compressive loads ranging from setback in a gun projectile to supersonic penetration into a hardened target. Cylindrical samples were heavily confined except for a moveable piston on one end. Piston and sample pressures were always measured, along with piston motion in several experiments to follow cavity collapse. With a 12.7-mm diameter by 6.3-mm deep cylindrical cavity in the sample, few of the 38 explosives examined survived at the higher loading rates. Usually a cast-cure or softer pressed explosive would deform without internal damage, and the reaction was mild and extinguished before consuming much of the sample. Melt-cast and the harder pressed explosives fracture suddenly and more vigorously react because of the additional surface area, sometimes even exploding. Reaction threshold and violence depended on the energetic ingredients and their particle size but also on mechanical properties related to the type of binder and fill density.
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