Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session U1: DSIC: Deflagration-to-detonation transition and hotspots |
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Chair: Blaine Asay, SNL / Springhill Room: Grand Ballroom I |
Thursday, June 20, 2019 3:15PM - 3:30PM |
U1.00001: The effect of quasi-static mechanical pre-load on deflagration violence in PBX 9501 Matthew Holmes, Gary Parker, Robert Broilo, Eric Heatwole, Trevor Feagin, Peter Schulze Sufficient localization of heat will lead to a nascent ignition hotspot in PBX 9501, and the ensuing post-ignition response may vary from extinguishment to detonation. Confinement has long been implicated as an essential factor affecting post-ignition violence. We present an experiment in which confinement is controlled as an independent variable. A disc of PBX 9501 is sandwiched between sapphire anvils with a controlled quasi-static pre-load and center-ignited with an infrared laser pulse focused through the bottom anvil. The post-ignition response is observed to vary as a function of the quasi-static pre-load, ranging from quench to flame propagation down gas-driven cracks at velocities of \textasciitilde 200 m/s. Above a threshold pre-load, pressure generated from product gases at the ignition site drives the formation and extension of radial cracks in the explosive. It is demonstrated that the dominant variable driving the early stages of deflagration violence is the gas confinement provided by a pressure seal formed by HE compression between the sapphire anvils. The results are placed within a context of drop/skid accident scenarios and place bounds on observed reaction violence of PBX 9501. [Preview Abstract] |
Thursday, June 20, 2019 3:30PM - 3:45PM |
U1.00002: Shock Compression Dynamics of Double-layer Explosive Charges Wei Zhang, Will Bassett, Meysam Akhtar, Lawrence Salvati, Dana Dlott In order to investigate the shock compression dynamics from sensitive explosive to insensitive explosive, double-layer polymer-bound explosive charges (PBXs) were prepared. The samples were composed of PETN and TATB-based PBXs with a poly(dimethylsiloxane) binder and charge diameters of 1.5 mm and 1.0 mm, respectively. The PBXs can be layered in varying thicknesses ranging from 25 $\mu $m to 200 $\mu $m. Experiments were designed such that the insensitive explosive is driven reproducibly by the small-scale detonation of the sensitive explosive in a booster-like geometry. More than one hundred individual shots can be taken on a single array. We use a tabletop laser-launched flyer plate apparatus to drive the initial reaction in the PETN-based PBX and measure the temperature with 32-channel pyrometry and the output shock wave using photon-Doppler velocimetry (PDV) with high time and space resolution as the reaction progresses through the booster and into the insensitive PBX. Two distinct emission bursts were observed on the ns and $\mu $s time scale and hot spot temperatures were calculated using the graybody model. [Preview Abstract] |
Thursday, June 20, 2019 3:45PM - 4:00PM |
U1.00003: Using Measured Hot Spot Temperatures in the Statistical Hot Spot Model Craig Tarver The missing link for developing realistic Arrhenius temperature dependent reaction rate laws for shock initiation and detonation reactive flow modeling was time resolved experimental measurements of unreacted hot spot, reacted hot spot, growing hot spot, and fully reacted reaction product temperatures. Recent measurements of such temperatures in several explosives by Bassett and Dlott have provided this data. This paper estimates the unreacted bulk shock, unreacted hot spot, reacted hot spot, and final reaction product temperatures for HMX and TATB as functions of shock strength. These temperatures are used to estimate Arrhenius reaction rates using actual activation energy barriers during shock to detonation transition. Such reaction rates will form the bases for macroscopic reaction rate schemes in the Statistical Hot Spot model. This work was performed under the auspices of the United States Department of Energy by the Lawrence Livermore National Laboratory under Contact DE-AC52-07NA27344. [Preview Abstract] |
Thursday, June 20, 2019 4:00PM - 4:15PM |
U1.00004: Investigating the evolution of the optical emission spectra of HMX with reaction regime Olivia J. Morley, David M. Williamson The optical emission of HMX was studied during the different reaction rates of burning, deflagration and detonation. For burning, the material was ignited by a butane flame in air at room temperature and atmospheric pressure leading to millisecond flares. A modified BAM impact test was used for deflagration, resulting in a 20 \textmu s impact-initiated partially confined reaction. Detonation was achieved with a column of HMX pressed to a density of 84 \textpm 2 {\%} TMD. PDV measurements allowed the CJ-pressure to be calculated at 24.0 \textpm 0.5 GPa, and the front velocity was measured at 7.8 \textpm 0.3 km/s. Burning showed the main spectral emission to be from alkali metal impurities, with the 589 nm sodium peak dominating the spectrum. With the higher reaction temperatures and pressures of deflagration, the redshift and broadening of this spectral peak were measured, along with the competing blackbody emission. From the spectra, temperatures of 4000 K to 5000 K in deflagration and 7000 K in detonation were calculated. This temperature increase is likely caused by the higher pressure shock at the start of the detonation front adiabatically compressing interstitial gases to greater temperatures than achievable with the chemical reaction alone. [Preview Abstract] |
Thursday, June 20, 2019 4:15PM - 4:30PM |
U1.00005: Modeling the shock-induced multiple reactions in a random bed of metallic granules in an energetic material Jack Yoh, Bohoon Kim, Sanghun Choi An investigation on the shock-particle interaction in condensed phase reactive flow has been carried out via the Eulerian hydrodynamic simulations. The analysis focused on the meso- to macro-scale numerical modeling of a granular metalized explosive containing randomly distributed metal particles intended to enhance its blast effect. The reactive flow model is used for the cyclotrimethylene-trinitramine (RDX) component, while thermally induced deflagration kinetics describes the aerobic reaction of the metal particles. The complex interfacial algorithm, which uses aligned level sets to track collapsing bubbles in water, is first validated against theory as well as experimental measurements. Then, the shock-induced collapse of metal particles embedded in the condensed phase domain of a high explosive is simulated. Both aluminized and copperized RDX are shown to detonate with a shock wave followed by the burning of the metal particles. The energy release and the afterburning behavior behind the detonating shock wave successfully identified the precursor that gave rise to the development of deflagration of the metal particles. [Preview Abstract] |
Thursday, June 20, 2019 4:30PM - 4:45PM |
U1.00006: Analysis of Chemistry in Reactive Molecular Dynamics Simulations Edward Kober The application of reactive molecular dynamics simulations to the reactions of energetic materials, especially for understanding ignition and deflagration processes in condensed phases, is now relatively common. However, the analyses of the reaction processes are often rather limited, restricted to following the appearance or disappearance of specific molecules. A more complete method of analysis is presented here. This is based on classifying each atom in the simulation by its coordination environment. This generates a countable matrix of geometry changes that can be formulated into a reduced chemistry model using Non-negative Matrix Factorization. This captures the general reaction characteristics (e.g. reduction of nitrogen, oxidation of carbon) in a series of correlated chemical waves. By analyzing simulations as a function of initial temperature and density, the Arrhenius reaction rates and thermodynamics properties can be extracted. Applications to HMX from ambient to detonation conditions using ReaxFF will be discussed. [Preview Abstract] |
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