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 1B: Equation of State and Phase Transitions |
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Room: Broadway I/II |
Sunday, June 16, 2019 10:45AM - 11:00AM |
1B.00001: Probing the Metastability Limit of Liquid Water under Dynamic Compression (symp) Michelle Marshall, Marius Millot, Dayne Fratanduono, Philip Myint, Jon Belof, Ray Smith, James McNaney Kinetics can play an important role in the transformation of materials to different high-pressure phases on the short time scales associated with dynamic-compression experiments. The study of phase-transition kinetics has motivated many theoretical and experimental works on the rapid freezing of water into the ice VII phase. We present measurements of the over-pressurization of the water-ice VII phase transition at 10$\times$ higher strain rates than previously studied. Water was ramp compressed to peak pressures of $\sim$15 GPa over $\sim$10 ns using a laser-driven release reservoir technique at the Omega Laser Facility. The stress at which water froze into the ice VII phase is deduced from wave-profile measurements and compared to predictions using a phase-transition-kinetics model recently developed at Lawrence Livermore National Laboratory. [Preview Abstract] |
Sunday, June 16, 2019 11:00AM - 11:15AM |
1B.00002: Shock driven decomposition and reshock in PMMA Meghan K. Lentz, Joshua D. Coe, Kirill Velizhanin \justify Polymethyl methacrylate (PMMA) is a transparent thermoplastic often used as a Hugoniot standard or as a window material in shock compression experiments. We present new equations of state (EOS) for solid PMMA based on the \texttt{Sesame} framework, and for its shock-driven decomposition products based on thermochemical modeling. We compare our results to a wide variety of existing data, finding good agreement in all cases. Previous proceedings (AIP Conference Proceedings \textbf{845}, 131 (2006)) described plate impact experiments in which PMMA was reshocked to pressures of up to $\sim$130 GPa, well above that at which it decomposes on its principal Hugoniot. These results were reanalyzed in a later proceeding (\emph{ibid}. \textbf{1426}, 771 (2012)), motivated largely by a higher than anticipated Gruneisen coefficient ($\Gamma$) inferred originally. We revisit this discussion based on hydrodynamic simulations performed with our new EOS. [Preview Abstract] |
Sunday, June 16, 2019 11:15AM - 11:30AM |
1B.00003: Predictive simulations of metastable phases of carbon at high compression Ashley Williams, Kien Nguyen Cong, Jonathan Willman, Nir Goldman, Ivan Oleynik Carbon exhibits a relatively simple phase diagram under hydrostatic compression: thermodynamically stable sp2-bonded graphite and metastable sp3-bonded cubic diamond at ambient conditions and bc8 and simple cubic phases at high pressures above 1 TPa. There have been reports of appearance of hexagonal phase of diamond in shock experiments, but these results have been questioned by interpreting associated diffraction peaks as deformation twinning on (111) planes as a result of plastic deformations in cubic diamond. We explore unknown metastable phases of carbon under both hydrostatic and uniaxial compression by using combination of first-principles density functional theory and semi-empirical density functional tight-binding combined with evolutionary crystal structure prediction. Shear stresses play a key role in transformation of diamond to new lower energy metastable phases. Their appearance provides a plausible interpretation of recent experimental observations. [Preview Abstract] |
Sunday, June 16, 2019 11:30AM - 11:45AM |
1B.00004: Hugoniot of Meso-Erythritol as an Inert Surrogate for PETN (symp) Zakary Wilde, Pedro Peralta Inert surrogates for high explosives provide low-risk options to understand basic material response to extreme conditions such as high pressure and high strain rates. Meso-Erythritol is under evaluation as a shock surrogate for Pentaerythritol Tetranitrate (PETN) due to their similar crystal structures and melting points. However, no Hugoniot data for Meso-Erythritol currently exists. Gas gun experiments will be performed to determine the Hugoniot of Meso-Erythritol as both power compacts and monolithic single crystals. Timing pins and VISAR will be used to measure the shock and particle velocities. Experiments will investigate particle velocities of up to 600 meters per second. The results will be compared to the Hugoniot of PETN to evaluate similarities in shock behavior. [Preview Abstract] |
Sunday, June 16, 2019 11:45AM - 12:00PM |
1B.00005: Molecular dynamics simulations of grain interactions in shock-compressed highly-textured columnar polycrystals Patrick Heighway, David McGonegle, Nigel Park, Andrew Higginbotham, Justin Wark When a polycrystal is shock-compressed, the grains of which it is composed cannot deform as they would do in isolation, but must do so in such a way as to accommodate the presence of their neighbours. This is to say that every grain must interact with those adjacent to it. While experimental studies abound demonstrating the range of physical effects that can be attributed to grain interactions under quasi-static loading conditions, little consideration appears to have been given to the detection of such interactions under the conditions of shock-loading. Here, we predict via molecular dynamics simulations the effect of grain interactions on the elastic strain state of a particular class of highly-textured polycrystal under shock-loading conditions. We find that cooperative elastic deformation of grains in directions transverse to the shock allows each crystallite to reach a state of reduced shear stress. We compare the extent of this relaxation for two different columnar geometries, in which the grains have either square or hexagonal cross-sections. Finally, we calculate the shifts in the x-ray diffraction (XRD) peaks that would result from these grain interactions, and hence assess the feasibility of detecting these interactions using ultrafast XRD techniques. [Preview Abstract] |
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