Hot-spot ignition mechanisms for explosives and propellants

TLDR

Explosives respond to stress and impact by generating hot‑spot sites, whose production mechanisms are the focus of this study. The authors examined single crystals, powders, pellets, gels, PBXs, and propellants using drop‑weight impact, transparent anvils, high‑speed photography, instrumented drop‑weight, miniaturized Hopkinson bar, laser speckle, automated speckle analysis, heat‑sensitive film, and microstructural polishing to observe hot‑spot formation. Ignition occurred at local hot‑spot sites, with evidence supporting adiabatic shear, gas‑cavity collapse heating, viscous flow, friction, fracture, particle shear, and triboluminescent discharge as possible mechanisms.

Abstract

This paper describes the response of explosives to stress and impact and in particular the mechanisms of ‘ hot-spot production. Samples in the form of single crystals, powder layers, pressed pellets, gels, polymer bonded explosives (PBXS) and propellants have been studied. Techniques used include a drop-weight facility with transparent anvils which allows photography at microsecond framing intervals, an instrumented drop-weight machine, a miniaturized Hopkinson bar system for high strain rate property measurement, laser speckle for studying the deformation and fracture of PBXS, an automated system for analysing speckle patterns and heat sensitive film for recording the positions and temperatures of hot spots. Polishing and staining methods have been developed to observe the microstructure of PBXS and failure during quasi-static loading. Ignition, when it occurred, took place at local hot-spot sites. Evidence is discussed for a variety of ignition mechanisms including adiabatic shear of the explosive, adiabatic heating of trapped gases during cavity collapse, viscous flow, friction, fracture and shear of added particles and triboluminescent discharge.