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 K6: TMS: First-principles and Molecular Dynamics IV |
Hide Abstracts |
Chair: Shailesh Mehta, AWE Room: Broadway III/IV |
Tuesday, June 18, 2019 2:00PM - 2:15PM |
K6.00001: Molecular dynamics study of shock waves in iron-carbon single crystals Hoang-Thien Luu, Nina Gunkelmann Shock compression experiments in pure iron show a three-wave structure: an elastic wave, a plastic wave and the phase-transformation from $\alpha $- to $\varepsilon $-iron. This three-wave structure has been confirmed by both experiments and molecular dynamics (MD) simulations. Large-scale MD studies provide insights into the transformation kinetics of iron including the transformation mechanisms, stacking faults and twins in $\varepsilon $-iron and the orientation dependence of iron single crystals. However, the influence of carbon on the transformation process remains an open topic. By atomistic simulations of high-strain rate compression of iron-carbon, we show that carbon decreases the elastic limit, but strongly increases the transformation pressure. We examine the role of carbon in the material transformation process under intense shock wave loading in Fe and Fe-C single crystals. [Preview Abstract] |
Tuesday, June 18, 2019 2:15PM - 2:30PM |
K6.00002: ABSTRACT WITHDRAWN |
Tuesday, June 18, 2019 2:30PM - 2:45PM |
K6.00003: Heating of tantalum upon shock breakout from a free surface P.G. Heighway, M. Sliwa, D. McGonegle, C. Wehrenberg, C.A. Bolme, J. Eggert, A. Higginbotham, A. Lazicki, H.-J. Lee, B. Nagler, H.-S. Park, R.E. Rudd, R.A. Smith, M.J. Suggit, D. Swift, F. Tavella, B.A. Remington, J.S. Wark The standard picture of uniaxial release from the shock state treats it as close to isentropic. As such, a sample shock-compressed to of order 100GPa pressures is expected to cool on release by several hundred degrees due to the thermoelastic effect. However, this fails to account for the approximately GPa strength of the rapidly-releasing material close to the rear surface, which thus suffers substantial heating from plastic work. Considerable energy can also be recovered via defect annihilation. We present MD simulations of shock and release in tantalum that exhibit release temperatures far exceeding those expected under the assumption of isentropic release. An energy-budget analysis shows that this is due primarily to plastic-work from material strength that largely counters thermoelastic cooling. The simulations are corroborated by experiments where the release temperatures of laser-shocked tantalum foils are deduced from their thermal strains via in femtosecond situ x-ray diffraction. [Preview Abstract] |
Tuesday, June 18, 2019 2:45PM - 3:00PM |
K6.00004: Anomalous Grain Size Dependence of Dynamic Mechanical Properties in Nanocrystalline SiC Ceramics Under Shock Loading Wanghui Li, Eric Hahn, Xiaohu Yao, Timothy Germann, Biao Feng, Xiaoqing Zhang Shock induced plasticity, structural phase transition, as well as dynamic damage and fracture in nanocrystalline SiC ceramics with grain size varying from \textasciitilde 2 to \textasciitilde 32 nm are investigated systematically by large scale molecular dynamics simulations with shock particle velocities varying from 1 to 5 km/s. Deformation twinning identified at Up $=$ 2 km/s decreases with decreasing grain size with a breakdown in the range from 10 to 6 nm of the grain size. Statistics from grain size effects on the phase transformation from Zinc-Blend to Rock-Salt structure at different particle velocities are obtained. Spall strengths are evaluated by an indirect free-surface method, akin to experimental measurements, and a direct method evaluating the atomic stress tensor at the point of spallation. An anomalous grain size dependence of the tensile strengths is revealed. The ultimate tensile strength decreases with decreasing grain size for all different particle velocities. However, the nucleation tensile stress at Up $=$ 1 km/s shows an inverse Hall-Petch (IHP) effect, and then a Hall-Petch (HP) relationship as the grain size is reduced, which shows similar to a theoretically predicted trend in nanoscale systems at high strain rate. [Preview Abstract] |
Tuesday, June 18, 2019 3:00PM - 3:15PM |
K6.00005: Nonequilibrium Molecular Dynamics Simulations of Ejecta Formation in Helium-Implanted Copper Rachel Flanagan, Saryu Fensin, Timother Germann, Marc Meyers The shock behavior of helium-implanted copper single crystals is investigated through non-equilibrium molecular dynamics simulations. Although copper has been well-studied by both experiments and simulations, its dynamic behavior containing heterogeneities such as helium continues to be of great interest to the materials science community. We specifically explore the production of ejecta, which is formed when a planar shock wave reaches a free surface. Both atomic helium and helium bubbles are randomly generated and implanted in a perfect fcc copper single crystal. The crystal is then shocked along the [111] direction using a controlled piston. We present results describing the dependence of ejected mass on the shock strength, as well as the size and velocity distributions of the ejected mass. LA-UR-18-26126 [Preview Abstract] |
Tuesday, June 18, 2019 3:15PM - 3:30PM |
K6.00006: Adaptations of Gurson-based ductile damage models for extreme dynamic loading Darby Luscher, Ted Carney, Miles Buechler There are several constitutive theories of ductile dynamic spallation ranging from relatively simple to quite sophisticated in their level of detail. Often these models are applied to a limited range of dynamic loading conditions. However, in many practical applications of dynamic material response, the material undergoes extreme shock compression such that other mechanisms are activated and confound the numerical robustness of the solution for damage evolution. We present theory and algorithmic adaptations of a Gurson-based modeling approach to address several numerical challenges. The theory is an extension of a previous model of Addessio and Johnson (1993). Implementations of Gurson-based models have used explicit or Newton-based implicit solvers, which work well with simple equations-of-state. These solvers often fail for nonlinear equations of state, e.g. with phase transformation. We present a solution strategy that is robust under large deformation within an ALE hydrocode and is compatible with general nonlinear equations of state. We demonstrate the efficacy of the approach through simulations of plate impact and explosively driven spallation experiments. Addessio and Johnson, Rate-dependent ductile failure model. J. App. Physics 74, 1640 (1993) [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700