Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session P6: EM.2 Shock Initiation |
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Chair: Jared Gump, Naval Surface Warfare Center - Indian Head Room: Cascade II |
Wednesday, July 10, 2013 11:00AM - 11:15AM |
P6.00001: Experiment and Reactive-Burn Modeling in the RDX Based Explosive XTX 8004 Carl Johnson, Michael Murphy, Richard Gustavsen XTX 8004 consists of 80 wt. {\%} cyclotrimethylenetrinitramine (RDX), and 20 wt. {\%} Sylgard 182, a silicone rubber used as a binder. Nominal density is 1.5 g/cm$^{3}$. We conducted four gas-gun driven plate-impact experiments that were instrumented with embedded electromagnetic particle velocity gauges. These provided wave profiles to which we calibrated an Ignition and Growth reactive burn model in ALE3D. A reactant Hugoniot and Pop-plot parameters were also extracted from the data and model calibration. Initiation of XTX 8004 in divergent flow was studied using SWIFT and photonic Doppler velocimetry (PDV). We used a gap test geometry in which the donor and acceptor charges consisted of cylinders of XTX 8004 nominally 4.65 mm in diameter by 15 mm long. Acceptor and donor were extruded into polymethylmethacrylate (PMMA) blocks and separated by a brass attenuator plate. Detonation and re-initiation (or failure) in the XTX 8004 was recorded using multiple SWIFT images of the position of the shock front in the PMMA. Input to the acceptor charge was estimated from PDV measurements of the free surface velocity of the attenuator plate, and output of the acceptor charge was also measured using PDV. Parameterization of Ignition {\&} Growth to 1-D vs. 2-D experiments will be discussed. [Preview Abstract] |
Wednesday, July 10, 2013 11:15AM - 11:30AM |
P6.00002: The increased shock sensitivity of PBX 9502 at high temperature Philip Rae, Eva Baca, Angelo Cartelli It has been shown previously that the shock sensitivity of TATB based PBXs can be significantly increased at elevated temperature. In fact, some researchers have reported that at 250$^{\circ}$C the Pop plot for LX-17 (a TATB based composition) overlays the Pop plot for room temperature PBX 9501 (an HMX based composition). The current study made use of the modified LANL small-scale gap test to investigate the shock sensitivity as a function of temperature. The modified gap test inputs an almost planar shock into the acceptor explosive rather than the more usual highly divergent one. This important change not only makes the geometry less sensitive to machining and assembly imperfections than a divergent version, but also allows accurate computer simulation using models calibrated to 1D Pop plot data. In these tests, samples of PBX 9502 were held at temperatures of 180, 200, 230 {\&} 260$^{\circ}$C for 30 minutes prior to firing the donor booster. As expected a significant increase in sensitivity was observed, but the material was not as sensitive as PBX 9501 even at 260$^{\circ}$C. The method of performing these more complex high temperature gap tests and the accompanying computer modeling of the results will also be presented. [Preview Abstract] |
Wednesday, July 10, 2013 11:30AM - 11:45AM |
P6.00003: Experiments and numerical simulations of plate gap model for high energetic materials Shiro Kubota, Tei Saburi, Yuji Ogata, Yuji Wada, Kunihito Nagayama The experimental system for this study consists of the pellet explosives and PMMA rings, PMMA pipe and booster explosive part. The pellets and the rings were alternately stacked in the PMMA pipe to make the system. The diameter of the pellet was 20 mm and the thicknesses were 10 or 5 mm. The thickness of the ring was varied to adjust the size of the air gaps between the pellets. The upper three pellet explosives were directly stacked without air gaps, and between the second and the third pellet, PVDF gauge was embedded to measure the arrival time of the detonation. The lower side pellet was put on the cylindrical stand made by PMMA, and the PVDF gauge was inserted between the pellet and PMMA to measure the arrival time of the detonation. Using the arrival times and a distance between two gauges, the average detonation velocity was estimated. The relationship between the size of the air gaps and detonation velocity was investigated. By changing both the gap size and the pellet, we consider that the system can roughly model the initial state of high energetic materials for qualitatively understanding of the initial state dependency. The detonation propagation processes in this system were simulated by our developed numerical code. [Preview Abstract] |
Wednesday, July 10, 2013 11:45AM - 12:00PM |
P6.00004: Effect of subcritical damage on sensitivity of a plastic bonded explosive George Sunny, Chad Rumchik, Jennifer Jordan, Thomas Krawietz As energetic materials are subjected to increasingly extreme environments, a more thorough understanding of the relationships between mechanical insult and changes in explosive sensitivity is desired. To that end, a Shock Wave Apparatus, originally developed at TDW (Schrobenhausen, Germany), has been employed to induce subcritical shocks of up to 0.7 GPa in a plastic bonded explosive sample while preserving the sample for further study. Changes in density due to the subcritical shocks are measured, and the sensitivity of the damaged explosive is determined through a TDW/AFRL Modified Gap Test configuration that allows the run-to-detonation (RTD) to be determined for a given shock loading. Changes in sensitivity are determined by comparing the RTD for each damaged sample with corresponding RTD for pristine (i.e. undamaged) samples. Confined Split-Hopkinson Pressure Bar experiments are also conducted in order to understand the effects of damage at lower strain-rates and pressures. Finally, the effects on sensitivity due to multiple shocks are also investigated in this study. [Preview Abstract] |
Wednesday, July 10, 2013 12:00PM - 12:15PM |
P6.00005: ABSTRACT WITHDRAWN |
Wednesday, July 10, 2013 12:15PM - 12:30PM |
P6.00006: Observation of sub-detonative responses in confined high density HMX-based PBXs Malcolm Cook, Andrew Wood, Philip Ottley, Phil Cheese This paper describes experiments and modelling aimed at understanding the behaviour of highly loaded (90{\%}-95{\%}) pressed HMX-based PBX compositions, when subjected to shock compression and ignition, by means of a propellant donor charge, under confinement. Such tests are routinely carried out in the UK on new formulations to determine their burn to violent reaction characteristics. The Bullseye propellant donor charge has been characterised in terms of pressure and temperature output. A range of tubes have been designed to examine the contribution of tube material properties (steel versus aluminium, 218.5MPa) and to examine the effect of reduced confinement (120MPa). For the reduced confinement scenario polycarbonate as well as steel and aluminium vessels have been designed which allow the reaction of the energetic material to be captured using high-speed video. In particular, tests carried out in the polycarbonate tubes have given a good insight of the processes occurring. Preliminary hydrocode modelling runs predicted an oscillating compressive wave in the explosive and considerable damage at either end of the explosive column. The latter leads to potential deconsolidation once the donor charge has burnt out allowing increased burning and violence. [Preview Abstract] |
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