Continuum modeling predictions of nonlinear specific heat in phase transition of energetic materials

We propose a chemo-thermal-mechanical model that considers phase transition phenomena, heat generation due to chemical reactions and mechanical deformations, and finite strain elasto-plastic behavior. We implement this highly nonlinear model in a state-of-the-art finite element solver. We study the chemical, thermal, and mechanical processes in the phase change of heterogeneous reactive materials at the microstructural level. The model is calibrated and applied to the HMX β→δ phase transition within plastic-bonded explosives. We present computational results such as chemical heating extrema, highly nonlinear and non-equilibrium specific heat, and accumulated plastic strain in representative unit cells for several volume fractions and heating histories. We show that particle volume fraction and sample heating rate are highly relevant for the pre-ignition response of plastic-bonded explosives to thermo-mechanical loads. We predict highly nonlinear specific heats for a finite system at the continuum level. Moreover, we utilize an analytic expression that estimates with a high degree of accuracy the critical temperature at which the maximum chemical heat release occurs.