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A micromechanics pressurization (MMP) model has been derived for explosive decomposition models that are pressure‐dependent. The model includes volumetric thermal strain and internal pressurization using well‐known solutions of elastic equations that include displacement of the condensed phase. The model is based on observations of a heated, high‐density, plastic bonded explosive (PBX) containing 95 wt% triaminotrinitrobenzene (TATB) with 5 wt% chlorotrifluoroethylene/vinylidene fluoride binder (Kel‐F). The model was developed for explosives that are either permeable or impermeable to decomposition gases. The MMP model is based on pore mechanics which describe reaction nucleation, decomposition chemistry, and elastic volumetric expansion. The model accounts for the expansion or swelling of the explosive into the surrounding gas‐filled ullage space. The pressurization model was used in conjunction with a simple decomposition model to determine ignition time and internal temperatures for the TATB‐based explosive at 1881 kg/m3. The MMP model was used to predict pressure, specific surface area, and gas volume fraction. A Latin hypercube sensitivity analysis showed that prediction of ignition time was most sensitive to the maximum pore pressure which defines the threshold between permeable and impermeable explosive layers. The MMP model coupled to a pressure‐dependent chemistry model can predict accurate ignition times for high‐density PBX's exposed to high temperatures and may be useful for more general application scenarios.

Ignition experiments from various sources, including our own laboratory, have been used to develop a simple four-step, pressure-dependent ignition model for PBX 9502, which is composed of 95% by mass triaminotrinitrobenzene (TATB) and a 5% by mass chlorotrifluoroethylene/vinylidine fluoride binder. The four-steps include drying, mono-furazan formation, and decomposition of mono-furazan and TATB into equilibrium products. Our experiments were both sealed and vented and included various ullage percentages ranging from 18% to 75% of unfilled confinement volume. Our sample densities ranged from 38% of the theoretical maximum density (TMD) to 98% TMD. We observed a decrease in ignition times with the higher density samples, an increase in ignition times with increased venting, and an increase in ignition times with increased ullage. From our experiments, we conclude that decomposition of PBX 9502 is pressure dependent, open pore decomposition occurs in low-density experiments, and that closed pore decomposition occurs when the samples are pressed to near full density. In some of our confined high-density experiments we have observed for the first time, multiple temperature excursions prior to ignition caused by internal pressure generation.

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A 2,4,6-trinitrotoluene (TNT) ignition model was developed using data from multiple sources. The one-step, first-order, pressure-dependent mechanism was used to predict ignition behavior from small- and large-scale experiments involving significant fluid motion. Bubbles created from decomposition gases were shown to cause vigorous boiling. The forced mixing caused by these bubbles was not modeled adequately using only free liquid convection. Thorough mixing and ample contact of the reactive species indicated that the TNT decomposition products were in equilibrium. The effect of impurities on the reaction rate was the primary uncertainty in the decomposition model.