Gas-induced defect evolution and ignition modeling of polymer-bonded explosives in slow cookoff

Understanding defect evolution and ignition in polymer-bonded explosives (PBXs) during slow cookoff is critical for thermal safety. This study develops a predictive model coupling gas transport with a micromechanics-based pressurization framework. A key innovation is the explicit distinction between pre-existing micropores and gas-induced opening-mode microcracks. We demonstrate that microcrack tip propagation dictates the onset of permeability, while the crack opening displacement regulates subsequent gas flow. The model successfully captures the localized pressure accumulation — a phenomenon driven by transport resistance — which significantly accelerates thermal decomposition. Validation against SITI and ODTX experimental data confirms the model's predictive accuracy and physical consistency. Furthermore, uncertainty quantification reveals high numerical robustness, showing that ignition time is minimally sensitive to microcrack parameters. Finally, statistical analysis of mesoscopic heterogeneity indicates that increased structural non-uniformity not only delays the median ignition time but also markedly amplifies its stochastic dispersion. This work provides a novel theoretical framework for gas-induced defect evolution, offering a robust tool for the thermal safety assessment of energetic materials.