Hot-spot ignition mechanisms for explosives and propellants

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.

Compaction waves in granular HMX

“…Material strength is negligble and a hydrodynamic model, as used in the simulation by Mader [2], suffices. At low pressures, comparable to the yield strength, other dissipative mechanisms are possible [7], such as plastic work, viscous heating in shear bands, and frictional heating at grain boundaries or along closed cracks. The dominant dissipative mechanism is likely to be application dependent.…”

Influence of temperature on the high-strain-rate mechanical behavior of PBX 9501

“…A significant number of previous studies have probed the constitutive response of a wide variety of plastic-bonded explosives (1)(2)(3)(4)(5)(6)(7)(8). Beginning with the high-rate Hopkinson split-bar studies of Hoge( 1) on a range of PBX's and continuing with the highstrain rate work of Field (3,5), Palmer(6), and…”

“…Beginning with the high-rate Hopkinson split-bar studies of Hoge( 1) on a range of PBX's and continuing with the highstrain rate work of Field (3,5), Palmer(6), and…”

Mechanistic Reactive Burn Modeling of Solid Explosives

“…The first is the applicability of the model to existing codes that are based mostly on the single-phase hydrodynamic equations. The second is the desire to focus on a unifying hot-spot model in view of the fact that there is virtually no agreement as to the mechanism or mechanisms by which the macroscopic mechanical energy is localized (Field et al 1992). As discussed in the first report (Yano et al 2001), it is nearly inconceivable that any single mechanism, be it pore collapse, friction, shear banding, or jetting will be same over the wide-ranging loading conditions.…”