Thermomechanically coupled microstructural evolution in polymer-bonded explosives: A 3D imaging and artificial intelligence-driven quantitative analysis

Abstract

Thermal-driven microstructural evolution in pressed polymer-bonded explosives (PBXs) critically impacts safety predictability. This study investigates the thermal decomposition characteristics of hexogen (RDX)-based pressed PBXs and the thermomechanical response of the binder through simultaneous thermal analysis and thermomechanical analysis. By integrating submicrometer-resolution 3D reconstructions obtained via x-ray microscopy (XRM), this study analyzes the temperature-dependent evolution of pore volume, sphericity, tortuosity, and pore-throat angles. The results reveal that pore evolution is controlled by the interplay between the softening-flow behavior of the binder and the reactivity of energetic crystals. The viscous flow of the binder at 160 °C minimizes both porosity (3.26%) and the average pore-throat angle of three-edge nodes (104.1°). At this temperature, the average pore volume is minimized with the most concentrated distribution, while sphericity peaks—microstructural features associated with enhanced safety potential based on reduced gas permeability and stress concentration mitigation. Beyond 160 °C, rising thermal stresses induce interfacial debonding, enhancing pore connectivity and degrading safety. The evolution of pore networks can be categorized into three phases: Isolated Closed-Pore Dominance Phase (T ≤ 160 °C), Pore Network Formation Phase (180 °C ≤ T ≤ 200 °C), and Structural Collapse Phase (T ≥ 210 °C). This study provides critical insights for the safety design and modeling of pressed PBXs under thermal loads, bridging microstructural dynamics to macroscopic risk assessment.