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 B3: First-Principles and Molecular Dynamics Calculations I: Metals I |
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Chair: Timothy Germann, Los Alamos National Laboratory Room: Renaissance Ballroom AB |
Monday, June 27, 2011 9:15AM - 9:30AM |
B3.00001: MD simulations of laser-induced ultrashort shock waves in nickel Ivan Oleynik, Brian Demaske, Vasily Zhakhovsky, Nail Inogamov, Carter White The dynamics of ultrashort shock waves induced by femtosecond laser pulses were explored in micron-sized nickel films by molecular dynamics simulations. Ultrafast laser heating causes stress-confinement, which is characterized by formation of a strongly pressurized 100-nm-thick zone just below the surface of the film. For low intensity laser pulses, only a single elastic shock wave was formed despite pressures several times greater than the experimental Hugoniot elastic limit. Since the material remains uniaxially compressed for less than 50 ps, comparatively slow processes of dislocation formation are not activated by the elastic shock wave. For high intensity laser pulses, the process of double wave breaking was observed with formation of a leading elastic shock preceding that of the plastic shock wave. Presence of a trailing rarefaction wave acts to attenuate the plastic shock until it disappears completely. The mechanisms of plastic deformation in the plastic front will be discussed. Agreement between the experimental and simulated plastic branch of the Hugoniot was facilitated by a new EAM potential designed to simulate nickel in a wide range of pressures. [Preview Abstract] |
Monday, June 27, 2011 9:30AM - 9:45AM |
B3.00002: Atomistic simulation of laser ablation of gold: the effects of electronic pressure Vladimir Stegailov, Sergey Starikov, Genri Norman In this work we study the ablation of gold foils irradiated by femtosecond laser pulses. We build an atomistic model of gold that capture electron heat conductivity, electron-ion energy transfer and the raise of the electronic pressure after energy deposition. The latter is done by means of the EAM potential for gold that parametrically depends on the electron temperature. The electronic pressure effects are shown to play an important role in the ablation processes and result in a new ablation mechanism observed in our simulations. The thickness of the ablation layer as a function of the irradiation fluence is calculated and compared with the experimental data. It is argued that the new ablation mechanism observed in this work can explain the known experimental discrepancies on the ablation data. [Preview Abstract] |
Monday, June 27, 2011 9:45AM - 10:15AM |
B3.00003: Spallation in metallic systems: Effects of microstructure, and loading pulse shape, rate and orientation Invited Speaker: The dynamic nature of spallation and the ubiquitous presence of microstructure may give rise to significant dependences on microstructure and loading, as indicated by indirect experimental observations. We present systematic, direct molecular dynamics (MD) simulations of spallation in metallic systems represented by Cu and a CuZr glass. The ``microstructure'' includes various defects in Cu, porous Cu, atomic-level inhomogeneities in the CuZr glass, and the Cu crystal$-$CuZr glass interfaces. We explore supported and decaying shock loading pulses, as well as different loading orientations. Tensile loading rates are changed via varying the flyer and target thicknesses in shock simulations, and more significantly (down to $\sim$10$^6$ s$^{-1}$), with accelerated MD simulations of single-void growth in Cu (mimicking shock). Our direct simulations reveal strong dependences of spallation on microstructure and loading, and quantitative dynamics of void nucleation/growth as well as mechanisms for plasticity, void nucleation and their interactions in the absence or presence of defects or interfaces. The future task of incorporating statistically the microstructure effects and their rate dependences into analytic models is of great interest to shock physics but a challenge. [Preview Abstract] |
Monday, June 27, 2011 10:15AM - 10:30AM |
B3.00004: Investigation of laser shock induced ductile damage at ultra-high strain rate by using large scale MD simulations Jean-Paul Cuq-Lelandais, Michel Boustie, Laurent Soulard, Laurent Berthe, Jo\"elle Bontaz-Carion, Thibaut de Resseguier Laser driven shocks allow to investigate materials behavior at very high strain rate (10$^{7}$s$^{-1})$ and presents a great interest for research applications. Microscopic simulations of ultra-short laser driven shock on micrometric Tantalum single-crystals have been performed by using the CEA-DAM Classical Molecular Dynamics code. This method, complementary to continuum models, provides an analysis the microscopic processes related to damage (ductile pore nucleation and growth) which occurs during spallation. This results are compared to spallation experiments data (VISAR signals, micro-tomography) obtained with the LULI100TW femtosecond laser in order to validate the MD behavior. Moreover, in the framework of a multi-scale approach, we show the possibility to use MD simulation to fit macroscopic damage models. This method is illustrated with an application to the parameters determination of the Kanel criterion. This also shows the high strain rates involved during damage process, around 10$^{9}$s$^{-1}$, allow to approach the inter-atomic theoretical cohesion stress threshold. [Preview Abstract] |
Monday, June 27, 2011 10:30AM - 10:45AM |
B3.00005: Ab initio study of mechanic, thermodynamic and transport properties of gold after electronic excitation Sergey Starikov, Vladimir Stegailov, Genri Norman, Oleg Sergeev, Petr Zhilyaev The electronic excitation after the femtosecond laser irradiation drastically changes mechanical and electronic properties of metals. In this work we calculate, on the example of gold, the effective interatomic potential in the EAM form that parametrically depends on the electron temperature. This potential is created by the force matching procedure based on the ab initio data calculated with the VASP package for the representative sets of atomic structures. The potential is verified by the recent experimental data. The electronic heat capacity, electronic conductivity and electron-phonon coupling constant are calculated at the DFT level using plane-wave pseudopotential approach. The dependence of these properties on the electron temperature and their deployment together with the new EAM potential in the two-temperature atomistic model of ablation are discussed. [Preview Abstract] |
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