Mechanisms of shock-induced initiation at micro-scale defects in energetic crystal-binder systems

TL;DR

This study uses high-resolution simulations to analyze how microstructural features in energetic crystal-binder systems contribute to shock-induced initiation, providing insights for safer and more reliable explosive design.

Contribution

The paper identifies and compares four key mechanisms of hotspot formation in PBXs through detailed numerical simulations, advancing understanding of initiation sensitivity.

Findings

Shock-focusing depends on crystal shape and shock strength.

Debonding at crystal-binder interfaces contributes to hotspot formation.

Void collapse within crystals and binders influences ignition.

Abstract

Crystals of energetic materials, such as HMX, embedded in plastic binders are the building blocks of plastic-bonded explosives. Such heterogeneous energetic materials contain microstructural features such as sharp corners, interfaces between crystal and binder, intra- and extra-granular voids, and other defects. Energy localization or hotspots arise during shock interaction with the microstructural heterogeneities, leading to the initiation of PBXs. In this paper, high-resolution numerical simulations are performed to elucidate the mechanistic details of shock-induced initiation in a PBX; we examine four different mechanisms: Shock-focusing at sharp corners or edges and its dependency on the shape of the crystal, and the strength of the applied shock; debonding between crystal and binder interfaces; collapse of voids in the binder located near an HMX crystal; and the collapse of voids within HMX crystals. Insights are obtained into the relative contributions of these mechanisms to the ignition and growth of hotspots. Understanding these mechanisms of energy localization and their relative importance for hotspot formation and initiation sensitivity of PBXs will aid in the design of energetic material-driven systems with controlled sensitivity, to prevent accidental initiation and ensure reliable performance.