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The decomposition of ,unconfined rigid polyurethane foam has been modeled by a kinetic bond-breaking scheme describing degradation of a primary polymer and formation of a thermally stable secondary polymer. The bond-breaking scheme is resolved using percolation theory to describe evolving polymer fragments. The polymer fragments vaporize according to individual vapor pressures. Kinetic parameters for the model were obtained from Thermal Gravimetric Analysis (TGA). The chemical structure of the foam was determined from the preparation techniques and ingredients used to synthesize the foam. Scale-up effects were investigated by simulating the response of an incident heat flux of 25 W/cm2 on a partially confined 8.8-cm diameter by 15-cm long right circular cylinder of foam that contained an encapsulated component. Predictions of center, midradial, and component temperatures, as well as regression of the foam surface, were in agreement with measurements using thermocouples and X-ray imaging.

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.