Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session V3: First-Principles and Molecular Dynamics Calculations X: Metals IV |
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Chair: Jean-Bernard Maillet, CEA, France Room: Renaissance Ballroom AB |
Thursday, June 30, 2011 4:00PM - 4:15PM |
V3.00001: Plastic Response of Grain Boundaries in Copper under Shock Loading Christian Brandl, Timothy C. Germann Previous molecular dynamics (MD) simulations have revealed that the preferred nucleation sites for dislocations at grain boundaries are related to the local atomic interface structure. Moreover, shock experiments discovered different post-mortem defect structures for low-energy and high-energy grain boundaries. In the present study, MD simulations are conducted to understand the structural origin of the differences in dislocation activity under shock compression, and failure upon unloading. We present MD simulations of shock loading conditions in copper bicrystals corresponding to grain boundaries studied in recent shock experiments of a columnar polycrystal. The defect structures produced in the MD studies are compared with the experimental post-mortem defect analysis, and the differences in the dynamic response are discussed in terms of the local grain boundary structures. [Preview Abstract] |
Thursday, June 30, 2011 4:15PM - 4:30PM |
V3.00002: MD simulations of steady shock wave propagation in nickel Brian Demaske, Vasily Zhakhovsky, Nail Inogamov, Carter White, Ivan Oleynik Shock waves in nickel were simulated by molecular dynamics using a new EAM potential specifically developed to accurately describe dynamic material response to high-strain-rate deformations. A combination of novel moving window technique and standard piston shock simulations were performed to study different regimes of shock propagation. Four distinct shock regimes were observed, including single elastic wave, split elastic and plastic shock waves, steady two-zone elastic-plastic single wave, and overdriven plastic wave, in order of increasing piston velocity. The novel two-zone elastic-plastic single wave consists of a leading low-pressure elastic zone, followed by a high-pressure plastic zone, both moving with the same speed and having a fixed net width that may extend to many microns. We will discuss the fundamental features of shock-wave structure, as well as the possibility of observing two-zone elastic-plastic single waves in experiment. [Preview Abstract] |
Thursday, June 30, 2011 4:30PM - 4:45PM |
V3.00003: An Atomistic View of Isentropic Compression Andrew Higginbotham, Giles Kimminau, Matthew Suggit, Justin Wark, Eduardo Bringa, Nigel Park, James Hawreliak, Jaime Marian, Evan Reed, Bruce Remington A great deal of importance is currently being placed on the use of ramp compression to achieve quasi-isentropic compression of solids to multi-megabar pressures in experiments which are of interest in planetary science and inertial confinement fusion. However, there is still relatively little work addressing what is perhaps the most important issue in this field of study; what is the difference between a shock and an isentrope? This apparently simple question is well defined and understood in a thermodynamic sense, but in the case of real materials, where a number of complex mechanisms may contribute to heat production during compression, the picture is somewhat more complex. We will show results from a number of molecular dynamics simulations aimed at understanding the generation of heat, at the lattice level, during ramp compression. Contributions from both elastic and plastic work will be isolated, allowing us to gain a better understanding of the microscopic processes involved. In addition, large scale simulations of ramp compression will be presented, and the pertinent timescales for quasi-isentropic compression of elasto-plastic materials will be discussed. [Preview Abstract] |
Thursday, June 30, 2011 4:45PM - 5:00PM |
V3.00004: Non-equilibrium Molecular Dynamics Studies of Interfacial Chemistry in Shocked Ni/Al Nanolaminates Jason Quenneville, Naresh N. Thadhani, Timothy C. Germann The response of Ni/Al composite materials to shock loading has been studied using non-equilibrium molecular dynamics and an EAM force field. The simulation cells consist of layered Ni and Al laminates with at least 3 million particles in a 1:1 mole ratio. The main thrust of our research is to gain a better understanding of the chemistry that occurs at the Ni/Al interface when the real material is shocked. Initial geometries were chosen so as to identify the factors important to reaction in the complex macro-scale material. Specifically, we vary the orientation of the interface with respect to the shock wave and the geometry of the interface ($i.e.$, deviation from planarity) to study how mixing and reactivity of Ni and Al are affected. Preliminary results show that peak pressure is greater when the shock direction is parallel to the Ni/Al interface plane, in agreement with results from continuum-scale simulations. Comparison of our computational results with experimental observations is an important part of this collaborative effort and is discussed in the paper. [Preview Abstract] |
Thursday, June 30, 2011 5:00PM - 5:15PM |
V3.00005: Richtmyer-Meshkov instabilities examined with large-scale molecular dynamics simulations Frank Cherne, Guy Dimonte, Timothy Germann We have performed a series of large scale classical molecular dynamics simulations with nearly 54 million atoms utilizing an embedded atom method potential for copper to examine the development of the Richtmyer-Meshkov (RM) instability. The calculations were performed at shock pressures between 82 GPa and 401 GPa which is both above and below the melt transition for copper. A sinusoidal profile with a 257 nm wavelength and varying amplitudes was created on the free surface of the simulated capper. We will show how the spikes and the bubbles grow as a function of amplitude and shock strength. For conditions where the copper is melted, we observe the growth of the RM instability into bubbles and spikes similar to fluid simulations. At conditions below the melt transition, certain amplitudes showed a series of accelerations/decelerations in the growth of the spike until a complete arrest of the spike growth occured due to the underlying strength of the material. [Preview Abstract] |
Thursday, June 30, 2011 5:15PM - 5:30PM |
V3.00006: Molecular dynamics simulation of dynamic response of beryllium Aidan P. Thompson, J. Matthew D. Lane, Michael P. Desjarlais, Albert P. Bartok, Gabor Csanyi The response of beryllium to dynamic loading has been extensively studied, both experimentally and theoretically, due to its importance in several technological areas. Compared to other metals, it is quite challenging to accurately represent the various anomalous behaviors of beryllium using classical interatomic potentials. We have used large-scale classical molecular dynamics simulations to study the response of single-crystal beryllium to high-strain rate uniaxial loading. We compare results from two different types of interatomic potential. A MEAM potential was constructed to reproduce properties of beryllium at ambient conditions. A potential based on the recently-developed GAP approach was fit to quantum simulations of solid and liquid beryllium phases near the shock-melting line. [Preview Abstract] |
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