Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session U1: DC-3: Modeling Shock Chemistry |
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Chair: Caroline Handley, AWE Room: Tennessee Ballroom C |
Thursday, July 2, 2009 11:00AM - 11:15AM |
U1.00001: Ellipsoidal Voids as a Trigger of Hot Spots in Solids Michael Grinfeld A characteristic feature of solid agglomerates as compared with liquid energetic materials is the possibility of localization of dissipation and adiabatic heating in the vicinity of inhomogeneities, especially, at crack tips, sharp corners, etc. Inhomogeneities of macroscopic size can be modeled by using a continuum approach which allows studying the reversible and irreversible effects responsible for generating hot spots. We explore the effects of appearance of stress driven hot spots in a systematic quantitative way. A closed-form analytical solution is obtained for ellipsoidal inclusions in isotropic media. Our model shows that the rate of thermomechanical dissipation of work essentially increases around penny-shaped ellipsoids. The paper also discusses some engineering aspects of the use of two-phase energetic materials with optimized geometry and density of inclusions. [Preview Abstract] |
Thursday, July 2, 2009 11:15AM - 11:30AM |
U1.00002: Vibrational energy transfer in shocked molecular crystals Joe Hooper The vibrational energy transfer behind a shock and its possible role in the earliest stages of explosive initiation is considered. A new theory of multiphonon energy transfer into shocked molecules is developed which expands on existing treatments and allows consideration of a range of molecular crystals and liquids. Simple analytic forms are derived for the change in this energy transfer with increasing Hugoniot pressure or near simple defects. The time required for the total shocked system to come to thermal equilibrium is found to be an order of magnitude or more faster than proposed in previous work, in good agreement with recent molecular dynamics calculations. In typical energetic molecular crystals, thermal equilibration is predicted to occur two to five picoseconds following passage of the shock wave. Simple defects are introduced into the model by considering the mesoscale elastic strain fields surrounding an inhomogeneity. For straight dislocations, a region of modestly enhanced energy transfer on the scale of five nanometers is found. However, due to the rapid establishment of thermal equilibrium, we find it is unlikely these regions are related to hot spot formation. Indeed, the theory developed here suggests that the effect of nonequilibrium phonon processes on sensitivity or initiation is minimal. [Preview Abstract] |
Thursday, July 2, 2009 11:30AM - 11:45AM |
U1.00003: On Delayed Detonation (XDT) Under Fragment Impact -- An Analysis of Experimental Data and a Simple Phenomenological Model Malcolm Cook, Peter Haskins Fragment and bullet impact pose a serious threat for many weapon systems because of their potential to induce violent reactions in the energetic materials (explosives and propellants) contained within them. In some scenarios detonations have been observed under conditions insufficient to cause SDT or DDT. These events have been labelled XDT (X for unknown, Detonation Transition). It has generally been assumed that XDT arises as the result of some combination of damage to the energetic material and re-shock or re-compression of this damaged material. In this paper we review the results of our previous experimental studies aimed at understanding the conditions under which XDT may occur as the result of fragment impact. In addition, we describe some new experiments with improved instrumentation to help elucidate the key processes. Based on the experimental evidence and some simple modelling we then propose a phenomenological model for the XDT process. [Preview Abstract] |
Thursday, July 2, 2009 11:45AM - 12:00PM |
U1.00004: Monte Carlo simulations of ionizing shock waves in argon Patrick O'Connor, Christopher Boswell The direct numerical simulation of shock-induced ionization was completed in order to determine the processes involved in the formation of explosively generated plasmas. The formation and structure of the ionizing shock, including flow instabilities and charge separation, were treated using a Monte Carlo method. Direct simulation Monte Carlo is a particle-based method used to model Boltzmann-like gas flows on a molecular scale by simulating systems containing thousands or millions of statistically representative particles. Interactions between neutral particles, ions, and electrons were encountered and involved hard-sphere and coulombic collisions, electron impact ionization events, and long-range magnetic and electrical forces. Simulation results will focus primarily on the coupling between the shock and the motion of the charged particles. Comparing these molecular level interactions to previous experimental work will provide additional interpretation of the effects of electric fields on shock wave behavior. [Preview Abstract] |
Thursday, July 2, 2009 12:00PM - 12:15PM |
U1.00005: Maximum Entropy of Effective Reaction Theory of Steady Non-ideal Detonation Simon Watt, Martin Braithwaite, William Byers Brown, Samuel Falle, Gary Sharpe According to the theory of Byers Brown, in a steady state detonation the entropy production between the shock and sonic locus is a maximum in a self-sustaining wave. This has shown to hold true for all one-dimensional cases. Applied to 2D steady curved detonation waves in a slab or cylindrical stick of explosive, Byers Brown suggested a novel variational approach for maximising the global entropy generation within the detonation driving zone, hence providing the solution of the self-sustaining detonation wave problem. Preliminary application of such a variational technique, albeit with simplfying assumptions, demonstrate its potential to provide a rapid and accurate solution method for the problem. In this paper, recent progress in the development of the 2D variational technique and validation of the maximum entropy concept are reported. The predictions of the theory are compared with high-resolution numerical simulations and with the predictions of existing Detonation Shock Dynamics theory. [Preview Abstract] |
Thursday, July 2, 2009 12:15PM - 12:30PM |
U1.00006: ABSTRACT WITHDRAWN |
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