Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session P21: Materials in Extremes: Energetic Materials and Reactive ChemistryFocus
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Sponsoring Units: GSCCM DCOMP DMP/DCP Chair: Igor Schweigert, Naval Research Laboratory Room: 320 |
Wednesday, March 16, 2016 2:30PM - 2:42PM |
P21.00001: Moving beyond feasibility in ultrafast shock chemistry experiments Michael Armstrong, James Lewicki, Jonathan Crowhurst, Joseph Zaug, Harry Radousky, Elissaios Stavrou, April Sawvel Although ultrafast hydrodynamic methods to investigate the chemistry of shocked materials on ps to ns time scales are generally mature, questions about the interpretation of such experiments remain. Most ultrafast experiments employ shock etalon methods whose interpretation depends on assumptions about the index of refraction of the shocked state. Further, although signatures for chemistry in longer time scale time-of-flight (ToF) experiments are well understood, ultrafast chemistry experiments have not typically employed ToF methods. The use of ToF methods in ultrafast experiments would enable a more straightforward connection to longer time scale data, and would generally provide more information than shock etalon methods. Finally, ultrafast experiments have not been performed over time scales greater than a few hundred of picoseconds, significantly limiting the scope of experiments to observe shocked chemistry under typical conditions at larger length scales. Here we address all of these issues by presenting data from shocked polymers obtained using both ToF and shock etalon methods, using a 1 ns pump and observation window. We compare the results of these two methods to reconcile data from these different methods and strengthen the interpretation of both types of experiment. [Preview Abstract] |
Wednesday, March 16, 2016 2:42PM - 2:54PM |
P21.00002: High-temperature thermal degradation of polyethylene from reactive molecular dynamics J. Matthew D. Lane, Nathan W. Moore Thermal degradation of polyethylene is studied under extremely high-rate temperature ramp rates from 10$^{14}$ to 10$^{10}$ K/s in isochoric, condensed phases. The molecular evolution and macroscopic state variables are extracted as a function of density from reactive molecular dynamics simulations using the ReaxFF potential. These results are used to parameterize a kinetic rate model for the dissociation and coalescence of hydrocarbons as a function of temperature, temperature ramp rate, and density. The results are contrasted to first-order random-scission macrokinetic models often assumed for pyrolysis of linear polyethylene under ambient conditions. Sandia National Laboratories is a multi program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04- 94AL85000. [Preview Abstract] |
Wednesday, March 16, 2016 2:54PM - 3:06PM |
P21.00003: ABSTRACT WITHDRAWN |
Wednesday, March 16, 2016 3:06PM - 3:18PM |
P21.00004: High-Velocity Collisions of Nanoparticles Donald Johnson, William Mattson Nanoparticles (NPs) are interesting materials with exciting applications due to their large surface-to-volume ratio and functionalizable surfaces. The large surface area and potentially high surface tension might result in unique materials behavior when subject to shock loading. Using density functional theory, we have simulated high-velocity NP collisions producing high-pressure, high-temperature, and extreme shock conditions. NPs composed of diamond-C, cubic-BN, and diamond-Si were considered with particle sizes up to 3.5 nm diameter. Some simulations involved NPs that were destabilized by incorporating internal strain. Normal, spherical NPs were carved out of bulk crystals and structurally optimized while the NPs with internal strain were constructed as a dense core (compressive strain) encompassed by a thin shell (tensile strain). Both on-axis and off-axis collisions were simulated at various speeds. Collision dynamics, shock propagation, and fragmentation will be presented and analyzed. The effect of material properties, internal strain, and collision velocity on the final temperature of the fragments will be discussed. [Preview Abstract] |
Wednesday, March 16, 2016 3:18PM - 3:30PM |
P21.00005: Non-equilibrium Reaction Kinetics in Molecular Solids Mitchell Wood, Alejandro Strachan We explore the possibility of non-statistical chemical reactions in condense-phase energetic materials via reactive molecular dynamics (MD) simulations. We characterize the response of three unique high energy density molecular crystals to different types of insults: electric fields of various frequencies (100-4000cm$^{-1})$ and strengths and direct heating at various rates. We find that non-equilibrium states can be created for short timescales when energy input targets specific vibrations through the electric fields, and that equilibration eventually occurs even while the insults remain present. Interestingly, for strong fields these relaxation timescales are comparable to those of the initial chemical decomposition of the molecules. Details of how this vibrational energy localization affects the preferred uni- or multi-molecular reactions are discussed. These results provide insight into non-equilibrium or coherent initiation of chemistry in the condensed phase that would of interest in fields ranging from catalysis to explosives. [Preview Abstract] |
Wednesday, March 16, 2016 3:30PM - 3:42PM |
P21.00006: Detonation Propagation in Slabs and Axisymmetric Rate Sticks Christopher Romick, Tariq Aslam Insensitive high explosives (IHE) have many benefits; however, these IHEs exhibit longer reaction zones than more conventional high explosives (HE). This makes IHEs less ideal explosives and more susceptible to edge effects as well as other performance degradation issues. Thus, there is a resulting reduction in the detonation speed within the explosive. Many HE computational models, e. g. WSD, SURF, CREST, have shock-dependent reaction rates. This dependency places a high value on having an accurate shock speed. In the common practice of shock-capturing, there is ambiguity in the shock-state due to smoothing of the shock-front. Moreover, obtaining an accurate shock speed with shock-capturing becomes prohibitively computationally expensive in multiple dimensions. The use of shock-fitting removes the ambiguity of the shock-state as it is one of the boundaries. As such, the required resolution for a given error in the detonation speed is less than with shock-capturing. This allows for further insight into performance degradation. A two-dimensional shock-fitting scheme has been developed for unconfined slabs and rate sticks of HE. The HE modeling is accomplished by Euler equations utilizing several models with single-step irreversible kinetics in slab and rate stick geometries. [Preview Abstract] |
Wednesday, March 16, 2016 3:42PM - 3:54PM |
P21.00007: Laser-shocked energetic materials with metal additives: evaluation of detonation performance Jennifer Gottfried, Eric Bukowski A focused, nanosecond-pulsed laser with sufficient energy to exceed the breakdown threshold of a material generates a laser-induced plasma with high peak temperatures, pressures, and shock velocities. Depending on the laser parameters and material properties, nanograms to micrograms of material is ablated, atomized, ionized and excited in the laser-induced plasma. The subsequent shock wave expansion into the air above the sample has been monitored using high-speed schlieren imaging in a recently developed technique, laser-induced air shock from energetic materials (LASEM) [1]. The estimated detonation velocities using LASEM agree well with published experimental values. A comparison of the measured shock velocities for various energetic materials including RDX, DNTF, and LLM-172 doped with Al or B to the detonation velocities predicted by CHEETAH for inert or active metal participation demonstrates that LASEM has potential for predicting the early time participation of metal additives in detonation events. The LASEM results show that reducing the amount of hydrogen present in B formulations increases the resulting detonation velocities. [1] J.L. Gottfried, Propellants Explos. Pyrotech. 40, 674 (2015). [Preview Abstract] |
Wednesday, March 16, 2016 3:54PM - 4:06PM |
P21.00008: The Equation of State of PBX 9502 Tariq Aslam Reactive flow modeling of high explosives (HEs) requires accurate equation of states (EOS) for both the HE's reactants and products. The Wescott-Stewart-Davis ``wide-ranging EOS'' model will be examined. A procedure for calibrating both the reactants and products for this EOS will be presented. Several thermodynamic pathways will be explored for the plastic bonded HE PBX 9502. These include: isothermal compression, isentropic compression, single and multiple shock compression, isobaric thermal expansion, adiabatic expansion of the products and the overdriven detonation state. Data from several different experimental techniques are employed to constrain model parameters. Validation tests of the model EOS will also be presented. [Preview Abstract] |
Wednesday, March 16, 2016 4:06PM - 4:18PM |
P21.00009: Measuring HOMO/LUMO gap of explosive film at air interface using ESFG: model for explosive at void surface Darcie Farrow, Ian Kohl, Sean Kearney, Stephen Rupper, Laura Martin, Kathy Alam, Robert Knepper, Jeffery Kay Vibrational broadband sum frequency generation has enabled measurements of heat transfer/disorder under shock compression on monolayer length scales (Carter, JPCA, 2008). At Sandia, we are extending this approach to examine shock-induced changes in the electronic structure of secondary explosives at surfaces using electronic sum frequency generation (ESFG)(Yamaguchi, JCP, 2008). Theoretical studies suggest explosives at voids and grain boundaries may have different reactivity than bulk material based on shifts in the bandgap at defects (Kuklja, Appl. Phys. A 2003). We seek to measure these electronic shifts for the first time using a thin film explosive samples as a model for the void surface. We will report electronic sum frequency data from vapour deposited thin film explosive compared to UV/Vis data of the bulk film at ambient pressures and discuss application of ESFG technique to samples under shock compression. [Preview Abstract] |
Wednesday, March 16, 2016 4:18PM - 4:30PM |
P21.00010: Shock wave propagation in semi-crystalline polyethylene: An atomic-scale investigation Robert M. Elder, Thomas C. O'Connor, In-Chul Yeh, Tanya L. Chantawansri, Timothy W. Sirk, Mark O. Robbins, Jan W. Andzelm Highly oriented polyethylene (PE) fibers are used in protection applications, therefore elucidation of their response under high strain-rate impact events is vital. Although PE fibers can have high crystallinity ($>$95\%), they also contain defects such as amorphous domains. Using molecular dynamics simulations, we investigate shock propagation through crystalline, amorphous, and semi-crystalline PE. We generate compressive shock waves of varying strength, quantify their dynamics, and characterize their effect on material properties at the atomic scale. In the semi-crystalline PE model, the differing density and molecular order of amorphous PE and crystalline PE result in differing shock impedances, which causes reflection and refraction of shock waves at interfaces between the phases. We quantify the properties (e.g. pressure, velocity) of the reflected and refracted waves, which differ from those of the incident wave, and compare with results from impedance matching. We also examine the reflection, absorption, and transmission of energy at the crystalline-amorphous interface. Depending on shock strength, amorphous defects can dissipate shock energy, which attenuates the shock and leads to effects such as localized heating. [Preview Abstract] |
Wednesday, March 16, 2016 4:30PM - 4:42PM |
P21.00011: Hierarchical Multiscale Framework for Materials Modeling: Advances in Scale-Bridging Applied to a Taylor Anvil Impact Test of RDX Brian Barnes, Kenneth Leiter, Richard Becker, Jaroslaw Knap, John Brennan As part of a multiscale modeling effort, we present progress on a challenge in continuum-scale modeling: the direct incorporation of complex molecular-level processes in the constitutive evaluation. In this initial phase of the research we use a concurrent scale-bridging approach, with a hierarchical multiscale framework running in parallel to couple a particle-based model (the "lower scale") computing the equation of state (EOS) to the constitutive response in a finite-element multi-physics simulation (the "upper scale"). The lower scale simulations of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) use a force-matched coarse-grain model and dissipative particle dynamics methods, and the upper scale simulation is of a Taylor anvil impact experiment. Results emphasize use of adaptive sampling (via dynamic kriging) that accelerates time to solution, and its comparison to fully "on the fly" runs. Work towards inclusion of a fully reactive EOS is also discussed. [Preview Abstract] |
Wednesday, March 16, 2016 4:42PM - 4:54PM |
P21.00012: Instantaneous Point Explosion in Incompressible Fluid-like Media Michael Grinfeld, Steven Segletes The problem of point explosion is one of the most famous and extensively developed in in the sense of corresponding physics, mechanics, and applied mathematics. There are many reasons for that based on its practical importance and theoretical beauty. We refer interested readers to the publications of Sedov, Taylor, Laudau and Lifshitz, and Lavrent'ev and Shabat. In the paper, we discuss this classical program from the standpoint of terminal ballistics and present our novel results relating to the special situation when the media can be treated as an ``effective'' incompressible liquid. Sedov, L.I., Similarity and Dimensional Methods in Mechanics, CRC Press, 1993. Taylor, J., Explosion. II. The Atomic Explosion of 1945. Proc. Roy. Soc. London, A201, ¹ 1065, 1950, p. 175. Landau, L.D. and Lifshitz, E.M., Fluid Mechanics, Pergamon Press, 1959. Zeldovich Ya. B. and Raizer, Yu.P., Physics of Shock Waves and High-Temperature Hydrodynamic Phenomena,Dover, New York, 2002. Lavrent'ev, M.A. and Shabat, B.V., Hydrodynamic Phenomena and Their Mathematical Models. Hauka, 1973 (in Russian). [Preview Abstract] |
Wednesday, March 16, 2016 4:54PM - 5:06PM |
P21.00013: \textbf{Impacts on Dissipative Sonic Vacuum} Yichao Xu, Vitali Nesterenko We investigate the propagating compression bell shape stress waves generated by the strikers with different masses impacting the sonic vacuum -- the discrete dissipative strongly nonlinear metamaterial with zero long wave sound speed. The metamaterial is composed of alternating steel disks and Nitrile O-rings. Being a solid material, it has exceptionally low speed of the investigated stress waves in the range of 50 -- 74 m/s, which is a few times smaller than the speed of sound or shock waves in air generated by blast. The shape of propagating stress waves was dramatically changed by the viscous dissipation. It prevented the incoming pulses from splitting into trains of solitary waves, a phenomenon characteristic of the non-dissipative strongly nonlinear discrete systems when the striker mass is larger than the cell mass. Both high-speed camera images and numerical simulations demonstrate the unusual rattling behavior of the top disk between the striker and the rest of the system. The linear momentum and energy from the striker were completely transferred to the metamaterial. This strongly nonlinear dissipative metamaterial can be designed for the optimal attenuation of dynamic loads generated by impact or contact explosion. [Preview Abstract] |
Wednesday, March 16, 2016 5:06PM - 5:18PM |
P21.00014: ABSTRACT WITHDRAWN |
Wednesday, March 16, 2016 5:18PM - 5:30PM |
P21.00015: Modeling the mechanical behavior of ceramic and heterophase structures manufactured using selective laser sintering and spark plasma sintering Vladimir A. Skripnyak, Evgeniya G. Skripnyak, Vladimir V. Skripnyak, Irina K. Vaganova A model for predicting mechanical properties of ultra-high temperature ceramics and composites manufactured by selective laser sintering (SLS) and spark plasma sintering (SPS) under shock loading is presented. The model takes into account the porous structure, the specific volume and average sizes of phases, and the temperature of sintering. Residual stresses in ceramic composites reinforced with particles of refractory borides, carbides and nitrides after SLS or SPS were calculated. It is shown that the spall strength of diboride-zirconium matrix composites can be increased by the decreasing of porosity and the introduction of inclusions of specially selected refractory strengthening phases. [Preview Abstract] |
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