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.
Die Erweiterung des Kriteriums fur die kritische Energie zur Voraussage der Grenzwerte der SchlagziindungEs ist lange angenommen worden, dal3 das Kriterium fur die kritische Energie, E,, von Walker und Wasley entwickelt, begrenzt ist sowohl auf den anwendbaren Druckbereich, als auch auf die Zahl der Sprengstoff-Formulierungen, die diesem Gesetz gehorchen. Die Einfuhrung einer spezifischen Grenz-Energie in das Kriterium ermoglicht dieses anzuwenden fur Sprengstoffe, die friiher als auRerhalb des Kriteriums liegend betrachtet wurden und ermoglicht den Schlagbereich, der durch das Kriterium fur Sprengstoffe die der E, genugen, erfal3t wird, innerhalb gewisser Druckgrenzen zu enveitern. Das neue Kriterium scheint besonders geeignet zu sein fur gegossene PBX-Formulierungen und fur unempfindliche Hochleistungssprengstoffe, wie TATB. Une extension du critkre de I'knergie critique pour pkvoir les seuils de I'amorgage par chocOn a longtemps supposC que le crithre de 1'Cnergie critique, Ec, dCveloppC par Walker et Wasley, ttait limit6 tant au domaine de pression auquel il s'applique qu'au nombre des formulations de l'explosif qui obtissent 5. cette loi. L'introduction d'une Cnergie limite sptcifique dans le critbre pennet de l'utiliser pour des explosifs que l'on considkrait auparavant comme n'appartenant pas au crithre et d'Ctendre, dans certaines limites de pression, le domaine d'impact couvert par le critbre pour les explosifs obCissant 2 Ec. Le nouveau critbre semble particulihrement adapt6 pour des formulations PBX coulCes et pour des explosifs CnergCtiques insensibles comme le TATB. SummaryIt has long been appreciated that the critical energy (&.) criterion, developed by Walker and Wasley"), has been limited in both the pressure range over which it applies"), and in the number of explosive formulations which appear to obey it"). The addition of a specific energy "cut-off' to the criterion enables it to be applied to explosives previously considered to lie outside the original criterion, and to extend the range of impacts covered by the criterion in explosives which obey E, within certain pressure limits. The new criterion appears particularly applicable to cast PBX formulations and insensitive high explosives such as TATB.
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.
The critical energy (Ec) criterion developed by Walker and Wasley for predicting the response of bare, heterogeneous explosives to flying‐plate impact, is modified for application to flat‐nosed rods and spherical projectiles. This modification redefines the shock duration term used in calculating Ec and implies that a minimum volume of explosive at a given shock energy is needed before initiation occurs. The modification also changes the L/D ratio of the projectile at which plate behaviour changes to rod behaviour from the currently accepted value of approximately 1/4 to 1/12. Comparisons between the modified criterion and published experimental data show that the same value of Ec can now be obtained from both flying‐plate and more complex projectile impacts into the same explosive.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.