Is the detonation “Dead Zone” really dead?

Abstract

This paper explores the Dead Zone (DZ) phenomenon in solid High Explosives (HEs), whereby weaker regions of a detonation shock fail to trigger prompt reaction, leaving behind them isolated pockets of substantially unburned explosive. A key unanswered question is the extent to which DZs react in the following flow, and whether they contribute a significant amount of energy on timescales relevant to system deconsolidation. This paper comprises two parts. The first surveys the DZ phenomenon and discusses (1) the multiple contexts in which it arises, (2) what is observed and believed about it, and (3) how it may be broadly categorized. This general perspective sets the stage for the second part, which examines in detail one particular DZ variant called transverse initiation. This case was not chosen because it is the most common or important, but because it is the most amenable to inquiry. (DZ quantification is quite difficult, and the presented experiment is apparently the first conceived to quantify DZs of any type.) The technique uses a modified Cylinder Expansion (CYLEX) test, wherein a faster HE core (PBX 9501, 95wt% HMX) is surrounded by a slower HE annulus (PBX 9502, 95wt% TATB). The fast HE drives detonation in the slow HE faster than the latter would naturally propagate; however, in doing so a largely unreacted initiation layer is left in the slow HE adjacent to the fast HE. Combining the usual CYLEX diagnostics with detonation front curvature measurements and invoking a novel analysis based on the Gurney and Taylor methods, the energy release vs time (and distance) is inferred. The result is a ∼0.3μs induction time (~3mm induction lag), after which the energy release rises in ∼2μs (15mm) to half its asymptotic value: ∼86% of the energy released by a PBX 9502 detonation.