Plastic Dissipation and Hot‐Spot Formation in HMX‐Based PBXs Subjected to Low Velocity Impact

Abstract

Low-velocity, shock-free impact is one of the accidental loads that can lead to a thermal explosion, the latter being the consequence of a chain of mechanisms depending on the microstructure of the material. To investigate the causes, the predictive capability of numerical tools depends on the physics embedded in the models. While a consensus has developed around the concept of hot spots, the exact nature of the thermo-mechanical heat-generating processes that preceded them remains to be clarified. We are studying a composition similar to the PBX 9501. HMX crystals are mixed with a few percent of a polymer binder. Recent experiments (reverse edge-on impact test) have revealed the influence of the plasticity of HMX grains even at low strain rates and low confinement. The heat released by the plastic dissipation has been identified as a potential candidate for the formation of hot spots. In this study, a numerical representation based on a polycrystalline β-HMX material subjected to intense shear is presented. Due to the high pressure generated by the impact, the intergranular slip is ignored. Emphasis is placed on the heterogeneity resulting from the micro-structural characteristics and the interaction between the anisotropic single crystals. The behavior of the binder and the influence of other heterogeneities such as friction or micro cracks are set aside. Finally, the mechanical dissipation is calculated in the models and the maximum temperature is deduced.

Elastic Coefficients of β-HMX as Functions of Pressure and Temperature from Molecular Dynamics

“…In the present study, we use MD to obtain elastic coefficients of β-HMX for wide intervals of temperature and hydrostatic pressure. The results obtained herein can be used both as a general reference and as input data for mesoscale continuum models of shock propagation and detonation initiation in β-HMX [11,12].…”

Pressure‐Dependent Chemical Decomposition of an HMX‐Based PBX During Low‐Velocity Impacts

“…This value does not reflect the vertical gradient of macroscopic pressure in the mold because neither the forces taken up at the wall by friction, nor the heterogeneity of the pressure at the microstructure level due to the anisotropy of the HMX crystals and their arrangement are taken into account. Although recent work suggests a future possibility of determining the pressure field in polycrystals [37–39], a simple method to evaluate this quantity is not available. On the other hand, the influence of friction can be evaluated from the static equilibrium of a slice of material using the following relationship: $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr p_{\left( z \right)} = p_{top\, } e^{{2 \over r}\mu {\nu \over {1 - \nu }}\left( {z - h} \right)} \hfill\cr}}$$$ …”

Peridynamic modeling of damage and non-shock ignition behavior of confined polymer bonded explosives under impact loading

“…It is often possible that the PBXs can be subjected to an unplanned stimulus such as impact with low velocity but sufficiently long durations during the handling, transport, and assembly of structures containing explosives. Therefore, a fundamental understanding of non-shock ignition response of PBX is important in safety assessments and it has received an increasing attention in the research community in recent years [3][4][5][6][7].…”