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 Y5: TMS: Modeling Thermal Response of Materials |
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Chair: David Kittel, SNL Room: Galleria North |
Friday, June 21, 2019 9:15AM - 9:30AM |
Y5.00001: Aqueous Glycine Condensation Chemistry Under Extreme Conditions Nir Goldman, Matthew Kroonblawd We have performed high throughput quantum molecular dynamics simulations to determine the free energy surface for aqueous glycine condensation reactions from moderate to extreme temperatures similar to oceanic hydrothermal vents (1g/cc and temperatures ranging from 300 K to 1000 K). Our simulations identify significant changes in the free energy surface topology and subsequent chemical reactivity with increasing temperature. We predict that temperatures at 400 K and below glycine favor dipeptide formation whereas higher temperatures facilitate the reverse hydrolysis reaction, with solvated glycine molecules showing greater stability. This change in favorability is correlated with a shift in the location and characteristics of specific reaction bottlenecks or barriers. Simultaneously, we observe that relative free energy barriers (total energy plus entropic contributions) for both condensation and hydrolysis reactions generally decrease with increasing temperature. Our results indicate that relatively modest temperatures near 400 K may best facilitate formation of oligoglycine molecules in oceanic systems related to the synthesis of life-building compounds. [Preview Abstract] |
Friday, June 21, 2019 9:30AM - 9:45AM |
Y5.00002: A reactive molecular dynamics study of phenol and phenolic polymers in extreme environments Keith A. Jones, J. Matthew D. Lane, Nathan W. Moore Phenolic polymers are key components in composite materials due to their ablative properties, oftentimes exposed to extreme conditions like heating and shock. The chemistry of phenolics under these conditions is not well understood. Phenolic polymers and phenol are studied with two parametrizations of the ReaxFF classical MD potential. We observe that the density of phenol in one parametrization, at six temperatures ranging from 123 K to 423 K, for which experimental density data are available, is in closer agreement with the experimental results. The accuracy of the density of phenol at various temperatures serves as a proxy for the ability of a parametrization to predict the density of a phenolic polymer under shock. Constant temperature pyrolysis of a phenolic polymer, modeled as a collection of linear chains, is then investigated with these two ReaxFF parametrizations at several temperatures ranging from 2000 to 3250 K. The activation energies for water formation, as well as the activation energy associated with the liberation of volatilizable compounds, are extracted and used as a point of comparison with experimental thermogravimetric analysis (TGA) results. The implications for determining the activation energy are discussed. [Preview Abstract] |
Friday, June 21, 2019 9:45AM - 10:00AM |
Y5.00003: Microstructure evolution of reactive powder mixtures during shock compression via two-point correlation functions Manny Gonzales, Austin Gerlt, Adam Pilchak, Eric Payton, Reji John, Michael Uchic, Sheldon Semiatin Reactive powder mixtures form heterogeneous multiphase networks and attain complex topologies during manufacturing. The microstructural topology of distended and fully dense reactive powder mixtures evolves during shock compression, and the response will depend on both the starting and intermediate microstructural configurations. This work employs two-point correlation functions along with meso-scale hydrocode simulations to capture the time-dependent microstructural topology of reactive powder mixtures. Real microstructures are extracted via montage serial sectioning from isostatically-compacted and extruded reactive powder mixtures of Ni$+$Al, Ti$+$Al, and Ti$+$B, which are used for direct numerical simulation of shock compression. Two-point correlations between phases and field variables link the starting microstructural configuration to the shock compression response. [Preview Abstract] |
Friday, June 21, 2019 10:00AM - 10:15AM |
Y5.00004: Modeling Pyrotechnic Explosions Allen Kuhl, David Grote We describe a hydrodynamic model of the flow field created by pyrotechnic explosions. It is based on a 3-phase version of our AMR code. It contains the following elements: (i) a gas-dynamic model of the expansion and mixing in the fireball, (ii) a Discrete Lagrangian Particles model of the burning projectiles, and (iii) a heterogeneous continuum model of the particle wakes. The 3 sets of conservation laws are coupled through drag and heat transfer with the gas; also, the projectiles loose mass, creating a mass source for the wakes. Adaptive Mesh Refinement: AMR (Bell et al., 1996) is used to capture turbulent mixing and combustion on the grid. The grid was initialized with similarity solutions for: (i) the detonation products (Kuhl 2015) and (ii) the particles (Stanyukovich 1960)—thereby defining the particular pyrotechnic charge configuration to be studied. The 3 sets of hyperbolic conservation laws were integrated with our high-order Godunov schemes (Bell et al. 1989). Results of the numerical simulations will be compared with data from pyrotechnic explosion tests. Most striking is the bright turbulent combustion structures in the fireball and the bright streamers formed by combustion of the DLP-wake systems. [Preview Abstract] |
Friday, June 21, 2019 10:15AM - 10:30AM |
Y5.00005: Afterburn modeling of nanothermite composites Serene Chan, Suceska Muhamed, Qingling Zhang, Kwee Liang Yeo, Huey Hoon Hng Typical approaches in modeling detonation in hydrocodes do not account for afterburn. The Jones-Wilkins-Lee (JWL) equation of state (EOS) captures detonation energy release but not the energy release from secondary combustion, known to increase overall energy output. There is a need for a modified EOS to account for burn mechanism of detonation and combustion products. One such modification was developed by Miller et al. [A reactive flow model with coupled reaction kinetics for detonation and combustion in non-ideal explosives, MRS Proceedings, 1995; p 413] whose reactive flow model caters for highly non-ideal explosives containing large amounts of metal, and display reaction kinetics characteristic of fast detonation and slow metal combustion chemistry. In this work, Miller's time-dependent JWL EOS was calibrated using a small scale test setup in which an explosive in contact with a nanothermite composite is detonated, and the wave propagation in water monitored using high speed camera. Based on thermochemical calculations of combustion and afterburn, and the calibration of reaction rate parameters from experimental results, a system-specific EOS can be determined. This methodology can potentially be applied to study the afterburning of other energetic materials. [Preview Abstract] |
Friday, June 21, 2019 10:30AM - 10:45AM |
Y5.00006: Simulations of the structure, vibrational spectra, and energy content of crystalline bis (4-amino-3,5-dinitropyrazolyl) methane under high pressures. Iskander G. Batyrev, Jonnathan C. Bennion, Jennifer A. Ciezak-Jenkins The crystalline structure of bis (4-amino-3,5-dinitropyrazolyl) methane (BDNAPM) was optimized from ambient pressure to 40 GPa using density functional calculations in order to understand pressure-induced instabilities. Raman spectra were calculated as a function of pressure using density functional perturbation theory and linear response for lattice dynamics. The zone center (k$=$0) optical modes provided information about the vibrational modes of the crystal. The calculated spectra were compared with high-pressure experimental spectroscopic measurements in the same pressure range. The enthalpy of formation was calculated along with the mass density for simulation of Chapman-Jouguet characteristics. [Preview Abstract] |
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