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 P3: High Pressure Strength I |
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Chair: Adam Schwartz, Lawrence Livermore National Laboratory Room: Renaissance Ballroom AB |
Wednesday, June 29, 2011 2:00PM - 2:30PM |
P3.00001: Dynamic Strength of Materials Invited Speaker: Historically when shock loading techniques became accessible in the early fifties it was assumed that materials behave like fluids implying that materials cannot support any shear stresses. Early and careful investigation in the sixties by G. R. Fowles in aluminum indicated otherwise. When he compared his Hugoniot compression measurements to hydrostatic pressure compression measurements in the pressure volume plane he noticed that the shock data lay above the hydrostatic compression curve -- which laid the ground work for what is the basis for elastic-plastic theories that exist today. In this talk, a brief historical perspective on strength measurements in materials will be discussed including how time-resolved techniques have played a role in allowing estimates of the strength of materials at over Mbar stress. This is crucial especially at high stresses since we are determining values that are small compared to the loading stress. Even though we have made considerable progress in our understanding of materials, there are still many anomalies and unanswered questions. Some of these anomalies are fertile grounds for further and future research and will be mentioned. [Preview Abstract] |
Wednesday, June 29, 2011 2:30PM - 2:45PM |
P3.00002: Material Mechanisms and Dynamic Loading Neil Bourne Matter respond to dynamic impulses with a variety of mechanisms. Each has it's own kinetics and threshold for operation triggered by the impulse applied. When a crystalline material is exposed to extremes of pressure such mechanisms include martensitic phase transformation, dislocation nucleation and propagation,~twinning and potentially melting. The length of the applied impulse thus determines the regimes of applicability of a physical model constructed from such data. A parameter is introduced to describe this quantity and is applied to examples drawn from a variety of crystalline responses showing the suite of available mechanisms and the range of observables that result. [Preview Abstract] |
Wednesday, June 29, 2011 2:45PM - 3:00PM |
P3.00003: Reshock and Release Response of Lithium Flouride to 21 GPa R. Stewart McWilliams Lithium Fluoride (LiF) is a material of unparalleled utility in dynamic loading experiments due to its good transparency at high pressure and it's consequent utility as an optical window. In experiments involving reloading and release from initially compressed states, a LiF window can be essential to the measurements but its mechanical properties, such as its strength at high pressure, may complicate interpretation of the results. To address this issue, experiments studying the reshock and release response of [100]-oriented LiF have been conducted for initial shock stresses from 7 to 21 GPa. The combined reshock and release data, interpreted in the context of the self-consistent model [J. R. Asay and J. Lipkin, J. Appl. Phys. 49 (7), 4242-4247, 1978], indicate a substantial increase in the strength of LiF above 7 GPa. A quasi-elastic reloading and unloading behavior similar to other dynamically-compressed solids is observed. Sound velocities in shock compressed LiF have also been measured. [Preview Abstract] |
Wednesday, June 29, 2011 3:00PM - 3:15PM |
P3.00004: Hugoniot-measurements of room- and high-temperature metals for study of EOS and strength Tsutomu Mashimo, Yuya Gomoto, Hideyuki Takashima, Mitsuru Murai, Akira Yoshiasa Pressure calibration in static high-pressure experiments has been undertaken on the basis of the EOS derived from the Hugoniot compression curves of metals (Au, Pt, Cu, W, etc.), MgO, etc. To obtain the strict EOS at room- and high-temperatures, we need to precisely measure the Hugoniot data, and access the strength and Gr\"uneisen parameter under shock compression. If the Hugoniot data of elevated temperature samples are measured, the high-temperature EOS can be accurately derived, and the Gr\"uneisen parameter can be directly discussed. The strength might decrease at high temperature. The Hugoniot-measurement experiments have been performed on single crystal Au, oxygen-free Cu, forged Ta and W by a streak photographic system equipped with a powder gun and two-stage light gas gun in the pressure range up to $>$200 GPa. In addition, the Hugoniot-measurement experiment of the elevated temperature samples was started using high-frequency heating on W, Au, etc. Some of the results will be presented, and the EOS and strength are discussed. [Preview Abstract] |
Wednesday, June 29, 2011 3:15PM - 3:30PM |
P3.00005: Reloading and Unloading Response of Shocked Aluminum Single Crystals: Time-Dependent Anisotropic Material Description J.M. Winey, J.N. Johnson, Y.M. Gupta To gain insight into the inelastic deformation mechanisms governing reloading and unloading of shocked Al, wave propagation simulations were performed for Al single crystals shocked to 13 GPa along [100], [110], and [111] directions. The simulations utilized a time-dependent anisotropic material model based on a dislocation dynamics description of shock- induced elastic-plastic deformation. The simulation results provide good qualitative agreement with the measured wave profile data [Huang and Asay, J. Appl. Phys. 101, 063550 (2007)], including reloading and unloading features previously identified with quasi-elastic response. Deviations from the ideal elastic-plastic response in shocked Al single crystals can be understood in terms of time-dependent material response. Therefore, a complete understanding of the reloading and unloading response of shocked polycrystalline solids may require consideration of both time-dependent response and material inhomogeneity (resulting in a distribution of shear stresses in the shocked state). Work supported by DOE/NNSA. [Preview Abstract] |
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