A time-resolved thermodynamic model for shock-induced chemical reactions in energetic structural materials

Abstract

Energetic structural materials (ESMs) have garnered considerable interest owing to their combination of structural strength and ability to release chemical energy. The energy release of ESMs under shock loading is primarily attributed to shock-induced chemical reactions (SICRs), which can cause significant deviations in the shock compression data from the Hugoniot curves predicted for inert counterparts. In this study, a time-resolved thermodynamic model was established to characterize the SICRs in ESMs. By decoupling the chemical reaction zone from the shock-wave front, the model resolves the transient thermomechanical states of the shock front and reaction zone. A reaction rate equation incorporating Arrhenius kinetics quantifies the energy release process, while a novel termination criterion based on the energy dissipation balance replaces the empirical thresholds. Validated against experimental Hugoniot data for porous Al/Ni and dense Al/CuO, the model successfully predicted reaction-induced shock-wave velocity enhancements and volume expansions. Based on the proposed model, the analysis revealed the following key findings: (1) elevated porosity lowers the reaction-onset pressure but attenuates detectable shock-wave velocity differences between reactive and inert responses, (2) for Johnson–Mehl–Avrami kinetics, activation energy Ea and mechanism exponent n are both governing factors, leading to different responses of reaction extent to shock temperature, (3) reaction zone width exhibits non-monotonic pressure dependence. The initial increase in the reaction zone width is followed by a decline beyond a critical pressure, with the dominant factors transitioning from the reaction extent to temperature. This theoretical framework enables modeling based on time-dependent physical quantities, further establishing a viable approach for determining reaction kinetic parameters using Hugoniot data, thereby creating opportunities for advancing research on ESMs and SICRs.