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 B1: TMS: HE Initiation I |
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Chair: Mitchel Wood, SNL Room: Grand Ballroom I |
Monday, June 17, 2019 9:15AM - 9:30AM |
B1.00001: Systematic study of the explosive chemical kinetics of derivatives of ETN and PETN at low pressure Marc Cawkwell, Romain Perriot, Virginia Manner The time-to-explosion of energetic materials as a function of temperature and pressure should follow Arrhenius kinetics. We have computed the activation energy and volume of a series of derivatives of erythritol tetranitrate (ETN) and pentaerythritol tetranitrate (PETN) to identify how modifications to the underlying chemistry affect sensitivity to explosion. The recently developed \textit{lanl}31 DFTB parameterization for organic materials was used to perform long-duration reactive molecular dynamics simulations of the derivatives. The simulations were performed in the microcanonical ensemble, which allows the time at which exothermic runaway occurs to be identified clearly. Multiple simulations were performed for each initial temperature and pressure to obtain representative statistics of the time-to-explosion. The effective activation energies and volumes that are obtained from the temperature and pressure dependence of the time-to-explosion are not chemically specific but instead represent the full set of reaction paths that occur prior to exothermic runaway in hot, condensed phase explosives. We compare the computed activation enthalpies to the results of experimental measurements of the relative sensitivities of the derivatives. [Preview Abstract] |
Monday, June 17, 2019 9:30AM - 9:45AM |
B1.00002: Nuclear Quantum Effects and their Role in Shock Induced Chemical Initiation of TATB Brenden W. Hamilton, Matthew P. Kroonblawd, Md Mahbubul Islam, Alejandro Strachan The approximation of classical ion dynamics in molecular dynamics (MD) leads to an overprediction of the specific heat and omits zero-point energy (ZPE). The former deficiency leads to an underprediction of temperature rise in MD shock simulations. Post-simulation corrections can accurately predict the actual rise in temperature, but do not correct for ZPE errors. We use ReaxFF and a quantum thermal bath coupled with the multiscale shock technique (MSST) to assess the separate roles of specific heat and ZPE in MD-based predictions for initiation of the explosive TATB. Compared to classical MSST simulations, the quantum bath not only increases the temperature rise that lowers the shock strength needed to induce chemical reactivity, but also leads to a decrease in the temperature threshold itself. Including ZPE lowers the apparent shock velocity threshold for reactivity by a similar amount as including a temperature-dependent specific heat. The decomposition pathways of TATB are shown to be unchanged by the quantum bath relative to predictions from purely classical simulations. Prepared by LLNL under Contract DE-AC52-07NA27344 and approved for unlimited release under document number LLNL-ABS-768122. [Preview Abstract] |
Monday, June 17, 2019 9:45AM - 10:00AM |
B1.00003: ReaxFF Predictions on Detonation Properties and Reaction Kinetics across the Energetic Materials Md Mahbubul Islam, Brenden Hamilton, Michael Sakano, Pilsun Yoo, Peilin Liao, Alejandro Strachan Developing predictive capabilities to determine detonation and kinetics properties, as well as chemical decomposition mechanism is crucial for designing new energetic materials (EM). We use ReaxFF molecular dynamics simulations with Hugoniostat technique to predict detonation velocities, Chapman-Jouguet pressures, and NVT cook-offs to calculate activation barriers in a range of EMs such as NM, TNT, TATB, RDX, HMX, PETN, and CL-20. We employ four ReaxFF parametrizations to assess the uncertainties associated with the predictions stemmed from the choice of force fields. Across the materials and force fields, our predicted detonation velocities are found to be within 7-18{\%} of the experiments and detonation products capture the trend in the experimental data. In order to further improve the accuracy of the predictions, we are currently working to incorporate atom and bond type dependent linear correction terms to the ReaxFF. The coefficients of the linear corrections are being fitted against the discrepancies in forces and energies between ReaxFF and quantum chemistry calculations. Such development will be an important step towards more accurate predictions of the properties of the EMs. [Preview Abstract] |
Monday, June 17, 2019 10:00AM - 10:15AM |
B1.00004: Study of equation of state and equilibrium mixtures Christopher Ticknor, Stephen Andrews, Dario Panici, Curtis Peterson, Viktor Turner, Jeffery Leiding We look at progress made in high explosive equation of state modeling at LANL. We present results on chemical equilibrium solvers used to study the evolution of a products equation of state. We will also present results for systematically improving the EOS parameters and models. In particular we look at polar molecules and their mixtures including ammonia and water systems. [Preview Abstract] |
Monday, June 17, 2019 10:15AM - 10:30AM |
B1.00005: ABSTRACT WITHDRAWN |
Monday, June 17, 2019 10:30AM - 10:45AM |
B1.00006: Non-Equilibrium Chemical Bonding of Shock-Induced Chemical Reactions. Anguang Hu Using multiresolution and multiscale quantum chemistry simulations recently developed, we demonstrated that dynamic non-equilibrium chemical bonding processes of shock-induced phase growth, mixing and detonations can take place between two Hugoniot adiabatic states of shock and detonation waves, representing reactant and product thermodynamic states. Such a process can start immediately on the onset when mechanical work couples thermal heat upon activation of reactive modes selected mainly by mechanical compression. Our preliminary results are in agreement with a number of shocked induced chemical transformations in terms of phase transition temperatures and pressures, for example, transformations of hexagonal diamond and boron nitride. Simulations also show unambiguous distinction between homogeneous and hot spot detonation reactions regarding shock leading pressure and temperature together with detonation densities. At lower pressure and density, it shows the hot spot mechanism with larger changes of bond lengths, leading to extremely higher temperature. In contrast, at larger pressure and density it shows homogeneous mechanism with small changes of bond lengths, resulting in relatively lower temperature. This is in good agreement of experimental observations. [Preview Abstract] |
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