Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session B7: Detonation Modeling |
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Chair: Caroline Handley, AWE, UK Room: Fairmont Orchid Hotel Promenade III |
Monday, June 25, 2007 10:30AM - 10:45AM |
B7.00001: Application of the CREST Reactive Burn Model to Two-Dimensional Explosive Experiments Nicholas Whitworth CREST is a new reactive burn model that uses entropy-dependent reaction rates to model shock initiation and detonation behaviour in plastic bonded explosives. To date the model has been applied to a wide range of shock initiation data obtained from explosive gas-gun experiments where one-dimensional, planar, flat-topped shocks are delivered to the explosive samples. In this paper, to provide a more rigorous test of CREST's predictive capability, the model is applied to two-dimensional explosive experiments where the shock wave entering the explosive departs from the ideal gas-gun case. The calculated results show that the model can simulate the explosive response in shock regimes that are markedly different from truly one- dimensional conditions. This gives confidence in the ability of CREST to simulate a wide range of shock initiation and detonation phenomena. [Preview Abstract] |
Monday, June 25, 2007 10:45AM - 11:00AM |
B7.00002: CREST for PBX9502 Caroline Handley CREST is a new reactive-burn model for explosives that is able to reproduce a range of shock initiation behaviour in conventional plastic bonded explosives. This is accomplished by using entropy rather than pressure-dependent reaction rates. In this paper, a CREST model for the insensitive high explosive PBX9502 is presented. The model is tested against a wide range of one-dimensional experimental data. [Preview Abstract] |
Monday, June 25, 2007 11:00AM - 11:15AM |
B7.00003: Generalized Pseudo-Reaction Zone Model for Non-Ideal Explosives Bradley Wescott The pseudo-reaction zone model was proposed to improve engineering scale simulations when using Detonation Shock Dynamics with high explosives that have a slow reaction component. In this work an extension of the pseudo-reaction zone model is developed for non-ideal explosives that propagate well below their steady-planar Chapman-Jouguet velocity. A programmed burn method utilizing Detonation Shock Dynamics and a detonation velocity dependent pseudo-reaction rate has been developed for non-ideal explosives and applied to the explosive mixture of ammonium nitrate and fuel oil (ANFO). The pseudo-reaction rate is calibrated to the experimentally obtained normal detonation velocity---shock curvature relation. The generalized pseudo-reaction zone model proposed here predicts the cylinder expansion to within 1{\%} by accounting for the slow reaction in ANFO. [Preview Abstract] |
Monday, June 25, 2007 11:15AM - 11:30AM |
B7.00004: Reactive Flow Calculation near a Free Boundary. Yehuda Partom In reactive flow calculations of detonation in a rod, an unreacted layer is formed at the boundary, affecting the diameter effect outcome. We investigate the origin of this boundary layer, and propose a simple and practical way to eliminate it. We show that it is an artifact of the finite rise time of the shock, caused by artificial viscosity. When the shock reaches a boundary cell, it releases right away, so that pressure and temperature there only reach a fraction of their shock levels, and the reaction rate is slow. We propose to remedy this artifact by delaying the boundary motion for a short while (40 nsec for a 10 cells per mm mesh) after arrival of the shock. In this way the boundary cells reach the appropriate pressure and temperature and react at the appropriate rate. In the paper we show how this remedy works. We compute detonation in a rod with different values of the boundary motion delay, compare the breakout curve from the far end with data from the literature, and obtain good agreement. This finite rise time effect near a low impedance boundary plays a role also in calculations of corner turning situations. But there the detonation borders with a dead zone, and the boundary contour is not known in advance. [Preview Abstract] |
Monday, June 25, 2007 11:30AM - 11:45AM |
B7.00005: A computational study of microstructure effects on shock ignition sensitivity of pressed RDX Yuichiro Hamate, Ruth Lu, Yasuyuki Horie There are many experimental measurements of microstructure effects on shock sensitivity and performance of solid explosives. But comparatively speaking, there are very few numerical models of these effects. This paper presents a computational experiment of microstructure effects using a recently developed model (Y. Hamate and Y. Horie, Shock Waves, V. 16, 125 (2006)). The model has been developed aiming at expanding predictive capability and applicability. To increase model capability, it is important to focus on physics-based approach, rather than parameter-fitting approach where non-physical parameter(s) needs to be re-calibrated for different set of conditions. Our model explicitly treats specific surface area with an assumption of exponential size distribution of hot-spots. Experimentally, Khasainov et al. discussed effects of specific surface area and found that both run distance to detonation and critical diameter have linear relation with reciprocal of specific surface area of HE. Computational experiments are carried out using pressed RDX model with various initial specific surface areas that are determined by average explosives particle size. The results demonstrate that both Pop-plots and critical diameter show the linear relation as observed by Khasainov et. al. [Preview Abstract] |
Monday, June 25, 2007 11:45AM - 12:00PM |
B7.00006: Physics-Based Reactive Burn Model: Grain size effects and binder effects Xia Lu, Yuichio Hamate, Yasuyuki Horie We have been developing a physics-based reactive burn (PBRB) model aiming at expanding predictive capability. The PBRB model was formulated based on the concept of a statistical hot spot cell. In the model, thermomechanics and physiochemical features are explicitly modeled. In this paper, we have extended the statistical hot spot model to explicitly describe the ignition and growth of hot spots. In particular, grain size effects are explicitly delineated through introduction of a size-dependent thickness of the hot-region thickness, a size-dependent energy deposition criterion, and a specific surface area. Besides the linear relationships between the run distance to detonation and critical diameter with the reciprocal specific surface area of HE, as discussed in a parallel paper in this meeting, parametric studies have also shown that the PBRB can predict a non-monotonous variation of shock sensitivity with grain size, as observed by Moulard et al. The purpose of this work is to extend the model to include the effects of explosive binders explicitly. As a first step we investigate the thermomechanical effects of a binder by using direct mesoscale simulations. The results will be used in the extending the PBRB model to include binder thermomechanics explicitly. [Preview Abstract] |
Monday, June 25, 2007 12:00PM - 12:15PM |
B7.00007: Multi-scale Statistical Design of High Energy Density Materials Joseph C. Foster, D. Scott Stewart, Keith Thomas High energy density materials [HEDM] find wide ranging application in commercial and defense applications. The engineering design of these materials is represented by a hierarchy of specifications on materials and processes. The specifications range in scale from molecular by specifying polymorphic crystal structure to macroscopic specifying geometry and global density. These specifications are used to control the configuration of the production HEDM component in the system design. A formalism analogous to that used in statistical mechanics is presented to aid in the interpretation of physical variability of the design based on specification. A multi-dimensional design space with restrictions imposed engineering specifications is proposed to construct an ensemble of specific designs represented by the variability allowed in the specifications. Based on a physical interpretation of the specifications and how they might apply to the physical function of the component; the formalism is intended to provide a well posed basis for the interpretation of design/ function relationships and fluctuations in behavior. [Preview Abstract] |
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