Meso-scale origins of the low-pressure equation of state and high rate mechanical properties of plastic bonded explosives

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Abstract
Most modern high explosives are formulated from a selection of energetic crystalline materials and plastics to create a material that accommodates the performance and sensitivity characteristic of the desired application. These materials are exposed to a variety of thermal-mechanical loads during their service life. Recent interest has focused research on safety and survivability under conditions that produce long duration, low amplitude loads as compared to the stimuli used to initiate detonation. The interest in the safety problem is on ignition of deflagration rather than initiation of detonation. A fully coupled thermal-mechanical-chemical kinetics representation of the problem is contained in a modified form of the Frank-Kamenetskii equations. Experimental techniques have been developed to characterize the low-pressure equation of state and the high-rate mechanical behavior of a representative material. This work addresses samples recovered from these experiments that have been subjected to extensive analysis using scanning electron microscopy (SEM). These data illustrate the presence of stress chains and stress bridging commonly observed in free particle beds among the high explosive particle embedded in the polymer. The mechanical and thermodynamic properties of the explosive crystal are quite different from those of the polymer. Significant inelastic response of the explosive crystal is apparent even in specimens that appear to have undergone only elastic deformation. The explosive crystals are clearly cleaved during the collapse of the stress bridges during the apparent elastic response of the bulk material.

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