An adaptive mesoscale ignition model for polymer bonded explosive under low velocity impact

Polymer bonded explosives (PBXs) are susceptible to unintended ignition under low velocity impact loading due to localized heating from crack friction and viscoplastic flow. Accurate modeling of this behavior requires resolving thermal processes at the micrometer scale while maintaining computational efficiency. This paper presents an adaptive mesoscale ignition model that addresses two critical challenges: the excessive computational cost of fixed large domains and the lack of physical basis for fixed-width heat source assumptions. The model features an adaptive computational domain that expands dynamically based on a temperature rise threshold, and an adaptive thermal loading scheme that automatically transitions from surface heat flux during solid friction to a volumetric heat source within the expanding molten region upon melting. Numerical examples demonstrate that employing a fixed heat load width results in significant deviations in ignition time, and the magnitude of the heat load significantly affects the equivalent width of the load region. Therefore, there is no universal optimal fixed value, which validates the superiority of the physics-based adaptive heat load strategy in this model. The proposed adaptive model offers a computationally efficient and physically consistent framework for predicting the mesoscale thermal ignition response once the local mechanical dissipation is provided, enabling robust integration into multi-scale safety assessments.