Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session E2: Detonations & Shock-Induced Chemistry II |
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Chair: David Frost, McGill University Room: Hyatt Regency Constellation C |
Monday, August 1, 2005 3:30PM - 3:45PM |
E2.00001: Extraction of Two-Dimensional Initiation Thresholds from Pop Plot Data Hugh James Unlike one-dimensional impacts, there is a close relationship between the Pop Plot and the two-dimensional initiation threshold for a given explosive. The reasons for this relationship are explored and estimates of the 2D threshold, obtained from what is a one-dimensional measurement (the Pop Plot), are compared with experimental results for a range of explosives. [Preview Abstract] |
Monday, August 1, 2005 3:45PM - 4:00PM |
E2.00002: DDT Characteristics of Laser Driven Exploding Bridgewire Detonators Eric Welle, Kevin Fleming, Robert Pahl The initiation and performance characteristics of Laser Exploding Bridgewire (LEBW) detonators loaded with CL-20, CP and BNCP were examined. LEBW devices, in name, as well as in function, exhibit similarities to their electrically driven counterparts with the exception that the means for energy deposition into the driving metal media results from photon absorption instead of electrical joule heating. CP and BNCP were chosen due to their well-known propensity to rapidly undergo a deflagration-to-detonation transition (DDT) and CL-20 was chosen to explore its utility as a DDT explosive. The explosive loading within the LEBW detonators were similar in nature to traditional EBW devices with regard to {\%}TMD loading of the initial increment as well as quantity of energetic materials. Comparisons of the energy fluences required for initiation of the explosives will be discussed. Additionally, streak camera measurements will be reviewed that were conducted at what would be considered ``hard-fire'' fluence levels as well as conditions closer to the mean firing fluence levels of initiation. [Preview Abstract] |
Monday, August 1, 2005 4:00PM - 4:15PM |
E2.00003: Measurements of the DDT Process in Laser and Exploding Bridgewire Detonators Eric Martin, Keith Thomas, Steven Clarke, D. Scott Stewart, Heather Mallett, James Kennedy, Alan Munger The deflagration-to-detonation transition of low density (0.88 g/cc) PETN during initiation by both an exploding bridgewire and laser driven source is being studied using both laser interferometry and streak photography. Cutback experiments using VISAR have confirmed a 1.0 mm run-distance to detonation in low density PETN powder. In a detonation system using a combination of low and high density powders, an apparent center of initiation (COI) analysis of streak data has yielded a surprisingly similar result. This data suggests that a compaction of low density powder to near theoretical maximum density (TMD) occurs before the onset of detonation, which is consistent with work done previously.$^{1}$ Additionally, data analysis shows that although function time increases significantly with decreasing firing voltage, the apparent COI changes very little. This indicates that the detonation criteria is not dependant upon the rate of deflagration, but on a volume of material that must be burned in a confined space to create the critical pressure needed at the compaction front. 1. M.J. Gifford, K. Tsembelis, {\&} J.E. Field, J. Appl. Phys. \underline {91}, 4995 (2002). [Preview Abstract] |
Monday, August 1, 2005 4:15PM - 4:30PM |
E2.00004: Observation of shock initiation process in gap test Shiro Kubota, Yuji Ogata, Yuji Wada, Katsumi Katoh, Tei Saburi, Masatake Yoshida, Kunihito Nagayama We have conducted the experiments for shock sensitivity of high energetic materials by gap test. The set up of gap test have been improved to observe the shock initiation phenomena in acceptor charge by high-speed camera. The length of gap material and length of acceptor are varied to observe the initiation process under various situations. The numerical simulations have also been conducted and compared with the experimental results to investigate the shock initiation criteria and the initiation model. We indicate that this improved gap test can be regarded the effective experiment to understand mechanism shock initiation process and to confirm the validity of the numerical results. [Preview Abstract] |
Monday, August 1, 2005 4:30PM - 5:00PM |
E2.00005: Statistical Hotspot Model for Explosive Detonation Invited Speaker: The presence and need for energy localization in the ignition and detonation of high explosives is a corner stone in our understanding of explosive behavior. This energy localization, known as hot spots, provides the match that starts the energetic response that is integral to the detonation. In our model, we use the life cycle of a hot spot to predict explosive response. This life cycle begins with a random distribution of inhomogeneities in the explosive that we describe as a potential hot spot. A shock wave can transform these into hot spots that can then grow by consuming the explosive around them. The fact that the shock wave can collapse a potential hot spot without causing ignition is required in order to model phenomena like dead pressing. The burn rate of the hot spot is taken directly from experimental data. In our approach we do not assume that every hot spot is burning in an identical environment, but rather we take a statistical approach to the burning process. We also do not make a uniform temperature assumption in order to close the mixture equation of state, but track the flow of energy from reactant to product. Finally, we include both the hot spot burn model and a thermal decomposition path, required to explain certain long time behaviors. Building on work performed by Reaugh et. al., we have developed a set of reaction parameters for an HMX based heterogeneous explosive. These parameters have been determined from computer models on the micron scale, and experimental data. This model will be compared to experimental rate stick data. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Monday, August 1, 2005 5:00PM - 5:15PM |
E2.00006: Prediction of Detonation in Non-Ideal Energetic Materials Elizabeth Cart, Richard Granholm, Vasant Joshi, Richard Lee, Phillip Miller, Harold Sandusky A predictive model of large-scale behavior for non-ideal energetic materials, based on measurements in small-scale tests is being developed using Dyna 2D. The growth criterion is based on the recently developed small-scale shock reactivity test (SSRT), whereas the time to reaction and the ignition conditions are derived from the newly developed hybrid split Hopkinson bar experiments. The reactivity tests measure the potential of a material to be an explosive regardless of its sensitivity, thus avoiding the problem of scale, inherent in most small-scale explosive tests. Large-scale test results are compared to calculations using the developed rate equation. The results of initial modeling work on a non-ideal PBX explosive will be validated using experimental results from two types of small-scale tests. [Preview Abstract] |
Monday, August 1, 2005 5:15PM - 5:30PM |
E2.00007: Mesoscale Probing of CRZ Structure in PBX: From Shock Ignition up to Detonation Failure Igor Plaksin, Jose Campos Paper reviews Portuguese contribution to the mesoscale study of PBX detonation which is being performed since 1996. We apply 96-channel optical analyzer for simultaneous measurements of light irradiation from detonation front (DF) surface and pressure field in chemical reaction zone (CRZ). This optical method, up to present, remains a unique diagnostic technique that offers the best compromise among high temporal and spatial resolution (600 ps and from 250 $\mu $m down to 50 $\mu $m respectively), large number of independent registration channels and design simplicity. This talk will address 3 major topics: dominant role of shear at shock initiation of PBX (results obtained in collaboration with NSWC-IH and LANL), origination of dissipative structures in CRZ of DW and related cellular structure of DF attended with ejecta (earlier recognized as DF ``roughness''), and relation between failure diameter and size of detonation cells. [Preview Abstract] |
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