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 N1: DSIC: Shock-induced chemical reactions |
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Chair: Dana Dattelbaum, LANL Room: Grand Ballroom I |
Wednesday, June 19, 2019 9:15AM - 9:30AM |
N1.00001: Examination of Shock-Induced Reaction in Ni/Al Powder Mixture Anirban Mandal, Matthew Beason, Brian Jensen Understanding the mechanisms of shock-induced reaction is important for gaining potential control over the synthesis of novel materials with enhanced properties. Toward this, planar shock wave responses of a physical mixture of Ni/Al powders and a composite Ni/Al powder produced through high-energy ball milling (HEBM) were compared. Powder samples pressed to 75{\%} TMD were shock compressed to peak pressures ranging between 10 -- 18 GPa and the resulting wave profiles were measured using laser velocimetry. Longitudinal stress -- particle velocity states in both powders, calculated from the measured wave profiles using impedance matching, lie along the inert Hugoniot constructed using McQueen's mixture theory. This suggests that the physical mixture and the ball-milled powder did not react within the duration of our measurements. Implications of this result on proposed shock-induced reaction mechanisms will be discussed. LA-UR-19-21418 [Preview Abstract] |
Wednesday, June 19, 2019 9:30AM - 9:45AM |
N1.00002: Hydrodynamic simulations of shock-driven chemistry in polyimide Jeffrey Peterson, Joshua Coe While the behavior of energetic materials has been extensively studied, the shock-driven chemistry of soft materials is still poorly understood. Analysis of recovered material from shock experiments has conclusively shown that soft materials undergo an irreversible transformation when shocked to high pressures, but only recently have in situ measurements of wave profiles [1] been able reveal the complex wave structures that result. In this presentation, we present hydrodynamic simulations that help connect observed wave behavior to interactions between thermodynamics, reaction kinetics, and hydrodynamics. As a prototypical example, we will present recent work with polyimide starting with a brief discussion of the equations of state created for both polyimide and its reaction products. The transition between reactants and products is achieved within the hydrodynamic simulation by utilizing a kinetic rate model whose parameters are informed through both historical shock data and more modern velocimetry measurements. Finally, we will discuss future directions for this work in the attempt to better reproduce experimental results. \newline \newline [1] Dattelbaum and Sheffield. AIP Conference Proceedings 1426, 627 (2012) [Preview Abstract] |
Wednesday, June 19, 2019 9:45AM - 10:00AM |
N1.00003: Spectroscopic Characterization and Burn Rate Measurements of Deflagrating High Explosives Suzanne Sheehe, Scott Jackson Physically based kinetic models are desirable to enhance the predictive capability of reaction zone (RZ) models for high explosives (HEs). Current models use only a 1- or 2-step reaction mechanism, which may not fully capture all relevant kinetic effects on deflagrative and detonative performance. The development of more physically accurate multi-step reaction models (containing both endothermic and exothermic steps) for HEs could dramatically improve the predictive range of models. Despite significant efforts to spectroscopically characterize detonating HE flows, progress has been limited due to the extremely temporally (20 ns) and spatially (200 micron) short detonation RZ scales, and high optical opacity. Deflagrations have significantly larger reaction zone scales (mm-sized), pressure-dependent burn rates (on the order of mm/s) and lower opacity at pressures in the MPa range. This readily enables spectroscopic characterization of key transient species critical in energy release. This work presents and discusses new results of emission spectroscopy and burn rate measurements in deflagrating HE (such as PBX 9407 and PBX 9502). [Preview Abstract] |
Wednesday, June 19, 2019 10:00AM - 10:15AM |
N1.00004: High resolution simulations of shock-induced combustion of Aluminum droplets Pratik Das, H.S. Udaykumar Post-detonation combustion of shock-dispersed aluminum particles in heterogeneous explosive charges is known to enhance energy deposition. We present a numerical scheme to compute the combustion of aluminum droplets in strongly shocked flows. The calculations include the effects of viscosity, surface tension and evaporation of the liquid into the surrounding gaseous phase, while treating the liquid-vapor interface in a sharp manner. A levelset based sharp-interface method is used to track the deformation of the droplet surface. A Riemann solver based ghost-fluid method (GFM) captures interactions at the sharp interface, by allowing characteristics waves to travel across the droplet interfaces, a technique that is well suited to handling strong shocks. The sharp-interface treatment ensures that the jump conditions for the viscous stresses at the interface are imposed with high fidelity. The model also includes chemical reactions at the surface of the Aluminum droplet. In addition, a nine-step reaction model is used in this work to compute shock-induced combustion of Aluminum in the gas phase. We show that the overall scheme allows for high-resolution simulations to understand the detailed physics of shock-induced combustion of droplets in gas streams. [Preview Abstract] |
Wednesday, June 19, 2019 10:15AM - 10:45AM |
N1.00005: Homogeneous initiation in single crystal PETN from shock induced bulk heating Invited Speaker: Bryan Henson Calculations of shock initiation in polycrystalline explosives convolve several phenomena. An input shock pressure $P$ generates compression and temperature ($V$, $T)$. The temperature, $T $(and possibly $P)$, determines the time to thermal ignition and the resulting rate of decomposition through a thermally activated Arrhenius rate and mechanism. The resulting rate of pressurization is further determined by the state of solid compression $V$ and the product pressure through the fliuid equation of state (EOS). This pressurization then determines the resulting shock physics that follows ignition, $e.g.$ wave coalescence, initiation. The simplest version of this problem in the solid state is the shock initiation of single crystal samples by homogeneous initiation. Here the relationship of ($V$,$T)$ in the reactant crystal is simplified by the absence of free volume and a quantitative relationship amongst ($P$,$V$,$T)$ through the solid EOS. In particular the possible states ($V$, $T)$ as a function of $P$ are constrained by the EOS. We present calculations of the time and distance to initiation as a function of input pressure in single crystal PETN. We use a JWL EOS for the solid to constrain the bulk temperature and compression as a function of impact pressure. We calculate the thermal ignition time as a function of temperature from a model of PETN thermal decomposition and the pressurization in the far field using a product fluid EOS and a simple application of the method of characteristics. We determine the unique ($V$, $T)$ state at each pressure by solving for the intersection of characteristics generated by the ignition and the input shock at the time and distance to initiation observed in experiments. Interesting results include the relationship between the input $T(P)$, the observation of multiple wave phenomena at low pressure and a mechanism for the nonlinearity in the measured pop-plot. [Preview Abstract] |
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