Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session L2: Material Science II |
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Chair: George T. Gray, Los Alamos National Laboratory Room: Fairmont Orchid Hotel Amphitheater |
Wednesday, June 27, 2007 8:00AM - 8:15AM |
L2.00001: Dislocation Mechanics Under Extreme Pressures Ronald Armstrong, Werner Arnold, Frank Zerilli The shock-induced plasticity of copper, Armco iron, and tantalum materials is attributed to strain rate control by a substantial dislocation density being generated at the shock front. A thermal activation type constitutive equation is employed for the dislocation generation based on achievement of a limiting small activation volume for the process. A linear dependence of the equivalent compressive stress on logarithm of the plastic strain rate is predicted. The prediction compares favorably with Swegle-Grady and Meyers measurements previously fitted to a power law relationship. For Armco iron and tantalum, control is matched with a dislocation description of deformation twinning at the shock front. By comparison, the uniform shock-less loading in an isentropic compression experiment (ICE) provides for plastic strain rate control by the drag-resisted movement of mobile dislocations within the resident dislocation density. [Preview Abstract] |
Wednesday, June 27, 2007 8:15AM - 8:30AM |
L2.00002: Initial Temperature Effects on the Shock Compression and Release Properties of Different Alumina-Filled Epoxy Compositions Mark Anderson, David Cox, Stephen Montgomery, Robert Setchell Alumina-filled epoxies are composites having constituents with highly dissimilar mechanical properties, resulting in complex behavior during shock compression and release. Two distinguishing characteristics are amplitude-dependent wave structures and high release velocities. Recent studies examined the effects of various compositional changes on these shock properties. As expected, the strongest effects were observed when the total alumina volume fraction was reduced in steps from a nominal 43{\%} to 0{\%}. In the present study, compositions prepared over the same range of alumina loadings were examined at initial temperatures from -50 to 70 $^{\circ}$C. Laser interferometry and wave timing were used to obtain transmitted wave profiles, Hugoniot states, and release wave velocities. Initial densities were determined from thermal expansion coefficients measured for each composition. Although initial density changes are very small, significant temperature effects on wave speeds and Hugoniot states were observed. [Preview Abstract] |
Wednesday, June 27, 2007 8:30AM - 8:45AM |
L2.00003: Taylor Impact Of Ti-6Al-4V Sam McDonald, Neil Bourne, George Gray, Jeremy Millett, Glenn Whiteman Over the past few years, a body of work has been performed to investigate the response of the titanium-based alloy, Ti-6Al-4V to one-dimensional shock loading. In this report, we take this work further including measurements of the shock response of the materials to one dimensional loading and by examining the behaviour of right cylinders of this alloy to high velocity impact onto a rigid surface with multiaxial loading. The results have been analyzed using a variety of techniques. In particular this work focuses on X-ray tomography that has been used to examine void formation immediately below the impact face due to interactions of releases, and other microstructural features from the cylinder edges. [Preview Abstract] |
Wednesday, June 27, 2007 8:45AM - 9:00AM |
L2.00004: Using Laser Induced Shock Waves to Investigate The Nanoparticle Transition From Bulk Behavior to Discrete Atom/Finite Size Behavior Bernard Gerstman As particle size becomes smaller, finite size effects become important and thermo-mechanical properties of nanoparticles, such as the bulk modulus, deviate from the values of larger size particles. The change in properties from the bulk values is important from an applied standpoint as nanoparticles are used in various applications and also important for testing fundamental models of atomic interactions in finite size systems. We develop a first principles model to predict all thermo-mechanical effects generated by any laser pulse incident on a nanoparticle. The use of short enough pulses produces shock fronts in the surrounding transparent medium that the nanoparticles are immersed in, such as water or a solid polymer. We show that, using particles of decreasing size, measurements of these shock fronts in the medium allow the determination of the size at which a nanoparticle is small enough to deviate from its bulk behavior and manifest finite size effects. Because the measurements can be made in the surrounding medium, they are easier to perform experimentally. [Preview Abstract] |
Wednesday, June 27, 2007 9:00AM - 9:15AM |
L2.00005: Influence of Peak Shock Stress on the Quasi-static Reload Response of HCP Metals E.K. Cerreta, G.T. Gray III, C.P. Trujillo, D.W. Brown, C.N. Tome Textured, crystal-bar-purity hafnium has been shock loaded at 5 and 10 GPa, below the pressure reported for the $\alpha \to \omega $ phase transformation, 23 GPa. The specimens were ``soft caught'' for post-shock characterization. The substructure of the shocked materials was investigated through optical and transmission electron microscopy and the texture evolution was probed with neutron diffraction. Shocked materials were reloaded quasi-statically in compression. The deformation behavior of as-annealed hafnium under quasi-static conditions is compared to its response following shock prestraining. The reload response is correlated to differences in defect density due to shock loading and compared with similar observations in other HCP metals. The microstructural development during quasi-static loading of the preshocked specimens is compared to that of the as-annealed specimens. [Preview Abstract] |
Wednesday, June 27, 2007 9:15AM - 9:30AM |
L2.00006: A Study of phase explosion of metal using high power Nd:YAG laser ablation Jack Y. Yoh, Hyunhee Lee, Kihong Kim The high speed blast wave generated by the laser ablation of metal reaches a propagation velocity of several thousand meters per second. The strikingly similar flow conditions to those of detonation wave allow one to apply the governing equations of motion for energetic materials to understand the explosive behavior of metal surface upon laser ablation. We describe the high power ($>$2.5 J/pulse) laser ablation technique for generating phase explosion for selective metals. The time resolved shadowgraph images of explosive wave fronts show that the point source (the targeted beam spot) blast wave radius is consistent with that given by the classical Sedov-Taylor solution. A multi-material shock physics code originally developed for high explosive detonation is applied for the full simulation of metal ablation based phase explosion. Some details on the experimental setup and the work-in-progress calculations are given. [Preview Abstract] |
Wednesday, June 27, 2007 9:30AM - 9:45AM |
L2.00007: Dynamics of the Onset of Damage in Metals under Shock Loading Aaron Koskelo, Scott Greenfield, Kenneth McClellan, Darrin Byler, Robert Dickerson, Dennis Paisley, Shengnian Luo, Damian Swift, Davis Tonks, Pedro Peralta We seek to understand the development of damage in polycrystalline materials under shock loading. Our current focus is on the role material microstructure plays in spall formation. Our approach is to use sensitive dynamic interferometry methods (see Greenfield's and Paisley's presentations at this meeting) to probe surface displacement and velocity dynamics of copper during shock loading using laser-launched flyers. Specimens have either columnar grains or have no more than one or two grain-boundaries between the spall layer and the surface that is monitored. In this way, we expect to unravel the complex surface dynamics observed in terms of loci for damage within the material. The dynamic measurements are to be correlated with pre- and post- shot materials characterization and damage assessment. Variables such as triple points, intergranular orientation mismatches, engineered inclusions and voids, and dynamic development of connections between voids are all part of our current work. This presentation will detail the results to date. [Preview Abstract] |
Wednesday, June 27, 2007 9:45AM - 10:00AM |
L2.00008: Deformation regimes in shocked nanocrystals: experiments and simulations Y.M. Wang, E. Bringa, A. Caro, M. Victoria, J. McNaney, J. Hawreliak, R. Smith, B. Remington, H. Lorenzana, M. Meyers, H. Jarmakani Transmission electron microscopy (TEM) of shocked nc samples shows dislocations for pure Ni with grain sizes above 30 nm grain, even at 70 GPa, which is more than twice the twinning threshold for shock-twinning in polycrystalline Ni. On the other hand, new experiments on NiW show a rich behavior, with twins only at 9 nm grain size and both dislocations and twins at grain sizes above 50 nm. We interpret this as due to the relatively low stacking fault energy (SFE) of NiW. A semi-analytical model is presented which is consistent with the experimental changes in the slip-twinning transition with grain size and stacking fault energy. MD of shock waves in nc Cu and nc Ni, which have very different SFE, are also consistent with the experimental results. The experiments, model and simulations provide a deformation map for nc under shock loading. [Preview Abstract] |
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