The shock and detonation response of high explosives has been an active research topic for more than a century. In recent years, high quality data from experiments using embedded gauges and other diagnostic techniques have inspired the development of a range of new high-fidelity computer models for explosives. The experiments and models have led to new insights, both at the continuum scale applicable to most shock and detonation experiments, and at the mesoscale relevant to hotspots and burning within explosive microstructures. This article reviews the continuum and mesoscale models, and their application to explosive phenomena, gaining insights to aid future model development and improved understanding of the physics of shock initiation and detonation propagation. In particular, it is argued that “desensitization” and the effect of porosity on high explosives can both be explained by the combined effect of thermodynamics and hydrodynamics, rather than the traditional hotspot-based explanations linked to pressure-dependent reaction rates.

Analysis of recent high quality, in-material gauge results from two cyclotetramethylene tetranitramine based explosives and one triamino trinitrobenzene based explosive has shown a number of significant correlations. These include the strong monotonic relationship between the local shock strength and the time to peak particle velocity along each particle path, and the simple scaling of velocity histories along the particle path that exists at a common local shock strength from shots with different initial conditions. Even shocks that have radically different evolutions, such as double shocks or those arising from thin pulses, show the same correlations once the catch-up of the second shock or rarefaction has occurred. From the correlations the strongest relationship is demonstrated to occur between the reaction and the local shock strength. Hence reaction, at least to first order, is a function of shock strength and time along the particle path, and is independent of local flow variables behind the shock such as pressure and temperature. Arguments are presented to suggest that shock entropy is the most likely measure of the shock strength which controls the reaction.

Abstract.CREST is an innovative reactive-burn model that has been developed at AWE for simulating shock initiation and detonation propagation behaviour in explosives. The model has a different basis from other reactive-burn models in that its reaction rate is independent of local flow variables behind the shock wave e.g. pressure and temperature. The foundation for CREST, based on a detailed analysis of data from particle-velocity gauge experiments, is that the reaction rate depends only on the local shock strength and the time since the shock passed. Since a measure of shock strength is the entropy of the non-reacted explosive, which remains constant behind a shock, CREST uses an entropydependent reaction rate. This paper will provide an overview of the CREST model and its predictive capability. In particular, it will be shown that the model can predict a wide range of experimental phenomena for both shock initiation (e.g. the effects of porosity and initial temperature on sustained-shock and thin-flyer initiation) and detonation propagation (e.g. the diameter effect curve and detonation failure cones) using a single set of coefficients.

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