Shock response and damage evolution of cyclotetramethylene tetranitramine (HMX) single crystals through finite element simulations

Energetic materials are substances with considerable amounts of energy that can detonate under shock, pressure, or high temperature conditions, making them acceptable candidates for applications such as explosives, propellants, and fuels. One example of an energetic material is the explosive known as cyclotetramethylene tetranitramine (HMX). When subjected to impact, HMX can undergo thermo-mechanical responses that may lead to deflagration or, in the most severe cases, detonation. Due to the multiscale nature of these phenomena and the varying impact velocity magnitudes, replicating such responses can be challenging or even unattainable in an experimental setting. Consequently, computational models capable of predicting real-world conditions beyond experimental reach are highly valuable to the explosives research community.

This study continues the work from previous analyses (Duarte 2021) by developing a finite element model of HMX combined with an aluminum rod, predicting damage evolution and dynamic response under shock compression. The impact velocities applied in the model ranged from 0.1 km/s to 0.6 km/s using three different crystal orientations to investigate their corresponding effects. The results indicate that impacting in the direction normal to the HMX plane [110], which exhibited high levels of plastic energy, had the most resistant to cracking near the HMX-aluminum interface. Furthermore, these findings show that elastic energy accumulation is the primary driver in this analysis of crack propagation and bulk damage in HMX crystals.

Additionally, the HMX and aluminum results were compared against two additional models: a homogeneous HMX sample without discontinuities and an HMX sample with a void in place of the aluminum rod. Comparisons of the models show that the most severe damage field occurs in the void model, while the shock wave accelerated through the aluminum rod but also decelerated significantly in the presence of a void due to wave refraction at traction free boundaries. These results provide another level of understanding into the role of material interfaces and voids in the dynamic response of HMX under shock loading. Experimental validation of these findings is recommended for future studies, assuming the conditions are feasible for testing.