Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session U2: Detonations and Shock-Induced Chemistry VII |
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Chair: Caroline Handley, Atomic Weapons Establishment Room: Grand Ballroom IV-V |
Thursday, June 30, 2011 2:00PM - 2:30PM |
U2.00001: Early-time thermal events behind a shock front and their relation to explosive initiation Invited Speaker: We consider the role, if any, of vibrational nonequilibrium in the ignition of solid explosives. Our recent theoretical work, as well as several large-scale molecular dynamics studies, all suggest that the initial nonequilibrium induced by a shock wave thermalizes far too quickly to influence shock initiation. In light of this, we examine some of the experimental correlations that have been cited as possible evidence that these nonequilibrium ``up-pumping'' processes may be involved in sensitivity. Particular attention is paid to recent studies of the vibrational anharmonicity and density of states of solid explosives based on temperature dependent Raman spectroscopy. Several authors have described good correlations between these properties and simple ignition tests such as a drop-weight impact. We investigate theoretically whether this correlation is even related to phonon-vibration up-pumping, or whether it is an artifact of unrelated aspects of the molecular decomposition kinetics and thermal transfer that occur during non-shock initiation. [Preview Abstract] |
Thursday, June 30, 2011 2:30PM - 2:45PM |
U2.00002: Numerical simulations for hot spot formation under shock loading in plastic-bonded explosives with three-dimensional discrete element methe Feng Zhao, Hailing Shang, Wenqiang Wang, Hua Fu Three-dimensional discrete element code, the combined discrete/finite element code and three-dimensional calculation model for explosive have been established for the simulation of hot spot formation in granular HMX, HMX based PBX, HMX crystalline with a void inside under shock loading. The simulation results indicate that in the case of PBX explosives hot spots mostly locate near the interface between HMX granules and binder, the temperature rise of HMX granules is lower than the binder, and the surrounding parts of HMX granules have higher temperature rise than the inner parts. In contrast to HMX granular explosive, since the binder can act as a cushion to the explosive, HMX in PBX has much lower temperature rise. Temperature of hot spot generated by void collapse is significantly influenced by the size and shape of the void. Finally, simple chemical reaction process has been simulated using the Arrhenius reactive rate law and the HOM equation of state for solid explosive and gas production. [Preview Abstract] |
Thursday, June 30, 2011 2:45PM - 3:00PM |
U2.00003: Short Shock Experiments and Modeling of Initiation in the HMX Based Explosive PBX 9501 Richard Gustavsen, Dana Dattelbaum, Caroline Handley, Carl Johnson, Stephen Sheffield, Lee Gibson We present results from a series of gas-gun driven plate impact experiments designed to measure the initiation response of PBX 9501 (95 wt.\% HMX, 2.5 wt.\% estane and 2.5 wt.\% nitroplasticizer) to short duration shocks. Embedded electromagnetic particle velocity gauges measured the reactive growth and initiation progress. Photonic Doppler Velocimetry (PDV) measured a particle velocity wave profile at the interface of the $\approx$ 23 mm thick PBX 9501 sample and a Lithium Fluoride (LiF) window. Impact stress in all three experiments was 4.4 GPa. Pulse durations of 0.5, 0.36, and 0.25 $\mu$s were created using 1.0, 0.75, and 0.5 mm thick Kel-F81 flyers backed by syntactic foam. The 0.5 $\mu$s pulse transited to detonation at $t_D=$ 2.08 $\mu$s, $x_D =$ 9.32 mm, considerably beyond the coordinates of $t_D=$ 1.4 $\mu$s, $x_D =$ 6.2 mm, expected for a long pulse. The 0.25 $\mu$s pulse failed to transition to detonation while the 0.36 $\mu$s pulse transitioned to a detonation at a position slightly less than the sample thickness of 23 mm. These experiments provide a more stringent test for reactive burn models than do the long pulse experiments used to generate the Pop-plot. [Preview Abstract] |
Thursday, June 30, 2011 3:00PM - 3:15PM |
U2.00004: Numerical exploration on the ignition mechanism of solid composite explosives in drop hammer test Zhi-Yue Liu Solid composite explosives are very popular forms of explosives for application at present. The sensitivity study on those explosives is of great importance for the safety and security either in usage or in storage. One conventional technique on the sensitivity is drop hammer test in which the explosive samples are subjected to the falling hammer impact to examine the occurrence of explosion. The falling height of the drop hammer from which the ignition is able to be incurred is usually taken for the characterization of impact sensitivity of those explosives. Friction and trapped-gas compression have been postulated as the two main mechanisms to cause the ignition of explosives. In the paper, a numerical approach is established to quantitatively verify the roles of such two factors in the process of ignition. In the analysis the composite explosive is assumed to be composed of the pile-up of circular particulate explosive crystals. The heat formation due to friction and trapped-gas compression is calculated. Combined with the ensuing heat conduction into crystal particulate, the whole decomposition process of the explosive particulate is analyzed to examine the possible ignition of the explosive samples. [Preview Abstract] |
Thursday, June 30, 2011 3:15PM - 3:30PM |
U2.00005: The Shock-Triggered Statistical Hot Spot Model Larry Hill The standard statistical hot spot (SHS) model assumes that all hot-spot-triggered burn waves initiate simultaneously within homogenized volume elements. In reality the shock passes through such elements, igniting burn waves in a phased manner. Simple simulations are employed to illustrate the resulting shock-triggered heterogeneous reaction structure. These demonstrate that the conventional continuum prescription is unlikely to be satisfied. An alternative strategy yields a robust continuum description, and enables an analytic solution that reduces to the standard SHS model result as the burn-front-to-shock-speed ratio approaches zero. The main effect of the shock-triggered correction is to increase the apparent state-sensitivity of the reaction rate. [Preview Abstract] |
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