Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session L3: ID-6: Nanocrystalline Metals, DU and BCC Metals |
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Chair: Sergey Razorenov, Institute of Problems of Chemical Physics, Russian Academy of Sciences Room: Hermitage C |
Tuesday, June 30, 2009 3:30PM - 3:45PM |
L3.00001: Response of Pt-based Bulk Metallic Glass to Shock Wave Compression B.M. LaLone, Y.M. Gupta Plate impact experiments were performed on platinum based bulk metallic glass (BMG) samples having a nominal composition of Pt$_{57.5}$Cu$_{14.7}$Ni$_{5.3}$P$_{22.5}$, a material previously reported to support large plastic strains under quasi-static, uniaxial stress loading (J. Schroers, and W. L. Johnson, Phys. Rev. Lett. \textbf{93,} 255506 (2004)). In the present shock wave experiments, peak longitudinal stresses ranged from 9-30 GPa. Piezoelectric pins and a velocity interferometer were used to measure shock velocities and particle velocity histories. A clear two-wave structure was observed in the particle velocity histories indicating an elastic-plastic response. The elastic wave amplitude was dependent on peak stress and sample thickness, with values ranging from 8.6 - 14.2 GPa. Measured wave profiles were converted to stress-density compression, and a nonlinear elastic model was fit to the measured elastic response. Unlike the quasi-static, uniaxial stress data on the same alloy, the shock wave, uniaxial strain results show a loss of strength above the elastic limit. Reasons for this strength loss are discussed. Work supported by the DOE. [Preview Abstract] |
Tuesday, June 30, 2009 3:45PM - 4:00PM |
L3.00002: Mechanical Behavior of Ultrafine-grained Titanium Alloys at High Strain Rates Vladimir Skripnyak, Evgenia Skripnyak Features of mechanical behavior of ultrafine-grained (UFG) titanium alloys under quasistatic and shock waves loadings with amplitudes less 10 GPa are discussed in this report. Mechanical behavior of VT1-0, Ti-6Al-4V, and Ti-6-22-22S alloys was studied by numerical simulation method. Results of simulation of high velocity impacts of plates of alloys with an average grain size 300 nm have a good accordance with experimental time-history profiles of free surface velocity. The multilevel model of mechanical behavior of structured materials was used for simulation. Model takes into account a several structural factors influencing on the mechanical behavior of materials (type of a crystal lattice, density of dislocations, a size of dislocation substructures, concentration and thickness of twins, and distribution of grains sizes). Results display the strain rate sensitivity of the yield stress of UFG and polycrystalline titanium alloys is various in a range from 10$^{3}$ up to 10$^{6}$ s$^{-1}$. Nevertheless the difference of the Hugoniot elastic limits of UFG and coarse grained titanium alloys is not considerable. [Preview Abstract] |
Tuesday, June 30, 2009 4:00PM - 4:15PM |
L3.00003: On probabilistic aspects in the dynamic degradation of ductile materials Gilles Roy, Herv\'e Trumel, Francois Hild, Yves-Patrick Pellegrini, Christophe Denoual Dynamic loadings produce high stress waves leading to the spallation of ductile materials such as aluminium, copper, magnesium or tantalum [1-3]. The main mechanism used to explain the change in the number of cavities with the stress rate is nucleation inhibition, induced by the growth of already nucleated cavities [4]. The dependence of the spall strength and critical time with the loading rate is investigated in the framework of a probabilistic model [4]. The present approach, which explains previous experimental findings on the strain rate dependence of the spall strength, is applied to analyze experimental data on tantalum [5]. \\[3pt] References: [1] Meyers M.A., Aimone C. T., 1983, ``Dynamic Fracture (Spalling) of Metals'', Prog. Mater. Sci., 18(1),pp. 1-96 [2] Curran D.R., Seaman L., Shockey D.A., 1987, ``Dynamic Fracture of Solids'', Phys. Rep., 147, pp. 253-388 [3] Grady D.E., 1988, ``The Spall Strength of Condensed Matter'', J. Mech. Phys. Sol., 36(3), pp. 353-384 [4] Trumel H., Hild F., Roy G., Pellegrini Y.-P., Denoual C., submitted to J. Mech. Phys. Sol., 2008. [5] Roy G., 2003, ``Vers une modelisation approfondie de l'endommagement dynamique ductile. Investigation experimentale d'une nuance de tantale et developpements theoriques'', Ph.D. Thesis, Poitiers University, France [Preview Abstract] |
Tuesday, June 30, 2009 4:15PM - 4:30PM |
L3.00004: Plasticity and Multimode Damage in Depleted Uranium Darcie D. Koller, Ellen K. Cerreta, George T. Gray III Recent damage studies on depleted uranium samples have revealed that the brittle type cracking typically observed in insipiently spalled depleted uranium samples contains a high level of plasticity as well. Experimental gas gun shock recovery results will be presented along with metallography from the recovered materials. Under dynamic tensile loading the nucleation and propagation of cracking is captured in the insipient state. Serial metallographic sectioning is performed and EBSD is used to observe the recovered state of the depleted uranium samples. Cracks appear to propagate in a mixed brittle and ductile mode. However, crack tips are shown to link up through regions of extremely localized plastic flow in the uni-axial loading direction. [Preview Abstract] |
Tuesday, June 30, 2009 4:30PM - 5:00PM |
L3.00005: Laser Compression of Nanocrystalline Metals Invited Speaker: Laser compression carried out at the Omega and Janus yields new~ information on the deformation mechanisms of nanocrystalline Ni. Although conventional deformation does not produce hardening, the extreme regime imparted by laser compression generates an increase in hardness, attributed to the residual dislocations observed in the structure by TEM. An analytical model is applied to predict the critical pressures for the cell-stacking-faults transition in single-crystalline nickel and the onset twinning in nanocrystalline nickel. The slip-twinning transition pressure is shifted from 20 GPa, for polycrystalline Ni, to 80 GPa, for Ni with g. s. of 10 nm. Contributions to the net strain from the mechanisms of plastic deformation (partials, perfect dislocations, twinning, and gb shear) were quantified in the nanocrystalline samples through MD calculations. The effect of release, a phenomenon often neglected in MD simulations, on dislocation behavior was established. A large fraction of the dislocations generated at the front are annihilated.\\[4pt] In collaboration with Hussam Jarmakani, University of California, San Diego; Eduardo Bringa, U. Nacional de Cuyo; Bruce Remington, Lawrence Livermore National Laboratory; V. Nhon, University of Illinois; P. Earhart and Morris Wang, Lawrence Livermore National Laboratory. [Preview Abstract] |
Tuesday, June 30, 2009 5:00PM - 5:15PM |
L3.00006: Flow stress of V, Mo, Ta, and W on nanosecond time scales Damian Swift, James Hawreliak, Bassem El-Dasher, James McNaney, Despina Milathianaki, Hector Lorenzana, Mukul Kumar, Bruce Remington, Thomas Tierney The mechanisms and kinetics of plastic flow in body-centered cubic materials are of current interest in the development of fundamental theories of dynamic strength, applicable at high strain rates such as are found in high explosive and laser loading. We have performed dynamic loading experiments with the Janus and Trident lasers, using tailored pulse shapes to induce shock or ramp loading. The response of the sample was investigated through the surface velocity history, and in some cases with in-situ x-ray diffraction. The velocity histories exhibited clear elastic waves, from which the flow stress was deduced and compared with the elastic strain as determined by diffraction. We compare the deduced flow stress with models calibrated to samples millimeters thick, and to theoretical studies. [Preview Abstract] |
Tuesday, June 30, 2009 5:15PM - 5:30PM |
L3.00007: Determination of Longitudinal and Bulk Sound Velocities in Natural Uranium under Shock-wave Loading Stanislav Finyushin, Alexey Fedorov, Anatoliy Mikhailov, Dmitriy Nazarov, Tatiana Govorunova, Denis Kalashnikov, Evgeniy Mikhailov, Vadim Knyazev We carried out the experiments on determination of longitudinal and bulk sound velocities in natural uranium in the range of pressures 40-72 GPa using laser interferometer Fabry-Perot. From the registered particle velocities profiles of contact boundary U-LiF the following parameters of elastic-plastic wave were defined: amplitude of elastic release wave 5.3-6.8 GPa, value of Poisson ratio 0.34-0.40, yield strength 0.96-1.36 GPa. It is shown, that influence of internal material structure is the cause of complex elastic-plastic behavior of natural uranium. [Preview Abstract] |
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