Porosity-controlled gas transport and ignition in slow cookoff of a polymer-bonded explosive

To investigate the effects of gas transport on ignition response of polymer-bonded explosives (PBXs) during slow cookoff, this study develops a thermo-mechanically coupled pyrolytic gas transport porous model. The model resolves dynamically coupled physical fields across thermal, mechanical, gas transport, and chemical reaction throughout the slow cook-off. Results are consistent with Sandia Instrumented Thermal Ignition (SITI) experiments for PBX 9501 in sealed and vented systems. It is revealed that porosity evolves in two stages: the first stage is dominated by thermal expansion, while the second is governed by decomposition. Gas transport pathways are controlled by the coupled evolution of porosity and temperature. Convective heat transfer from gas products contributes less of the total thermal transport, while the concentration effect of gas product within pores is identified as the dominant factor in ignition delay. This study provides a foundational framework for understanding gas transport in the slow cookoff of polymer-bonded explosives.