The CREST reactive-burn model for explosives

Abstract

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.

Numerical modelling of steady detonations with the CREST reactive burn model

“…Figure 4a shows the diameter effect curve for EDC37 with the CREST reaction rate given by Eqs. (8) to (12). It can be seen that the DNS results lie between those from the DSD approximation and SSA.…”

“…The equations governing the chemical reaction rate are also empirical and are typically calibrated with ignition timing and size-effect data [4,5]. The reaction rates are generally related to the shock strength via a dependence upon one of the thermodynamic variables, such as pressure [6], temperature [7] and entropy [8].…”

“…It has been shown that CREST can accurately reproduce run-time to detonation and radius effect curves [16]. DNS have been carried out using this model [8,[16][17][18], but it has not yet been combined with any steady state detonation models such as the Wood-Kirkwood model or DSD. The two phases in the equation of state are an unreacted solid phase and a fully reacted gaseous phase.…”

“…The reaction rate model consists of a fast reaction associated with "hot-spots", with a reaction progress variable λ 1 , which activates a slow bulk reaction, described by λ 2 . The reaction rates [8] are…”

A complete equation of state for non-ideal condensed phase explosives

“…The leading shock at the front of a detonation wave compresses the material to volumes significantly smaller than the crushing volume. As such it is adequate to adapt the reference curves of the reactant EoS following the snow plow model 24,25 . The compressibility of the material at volumes larger than the crushing specific volume is taken to be infinity.…”