Mesoscale Numerical Analysis of Thermal-mechanical-chemical Responses of Polymer-bonded Explosives under Impact Loading

We developed a mesoscopic reactive model for cyclotetramethylene tetranitramine (HMX) single crystal, which incorporates nonlinear anisotropic elasticity, crystal plasticity, and temperature-dependent chemical reaction. Together with a viscoelasticity model for the polymer binder - Estane 5703, the proposed models were implemented in the finite element code ABAQUS by the user subroutine VUMAT. Mesoscale heterogeneous PBX 9501 samples were constructed and loaded under low-strength impact scenarios from 100 m/s to 600 m/s. Mesoscale thermal-mechanical-chemical responses (stress, temperature, and extent of reaction) are analyzed and homogenized across the microstructure to obtain the response at the macroscale. Results show that crystal anisotropy and microstructural heterogeneity are responsible for the nonuniform stress field and fluctuations of the stress wave front. At a critical impact velocity (> 300 m/s), a chemical reaction is triggered because the temperature contributed by the volumetric and dislocation-based plastic works is sufficiently high, which may lead to the ignition or detonation. By comparing with the macroscale experimental measurements, the results presented here can help to develop a more accurate physical-related continuum model in the future. Moreover, this framework has important implications in understanding hot spot ignition processes and improving predictive capabilities in energetic materials.