Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session H42: Focus Session: Dynamic Compression |
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Sponsoring Units: GSCCM DCMP Chair: Hector Lorenzana, Lawrence Livermore National Laboratory Room: Baltimore Convention Center 345 |
Tuesday, March 14, 2006 11:15AM - 11:51AM |
H42.00001: Analyzing Isentropic Compression Wave Experiments Invited Speaker: Some common assumptions that are used to analyze shock wave experiments are inadequate for analyzing ramp wave compression experiments. Analysis of a Doppler shift through a window usually assumes a steady wave in the window, a condition that is violated when a ramp compression wave steepens as it propagates, requiring separate consideration during the analysis (LiF to 20GPa). Introduction of a free or windowed interface produces large perturbations to the flow in the sample that must be reconciled to achieve required timing accuracy: when the specimen has a unique stress-strain compression relation, the equations of motion are hyperbolic so that stress-strain relation can be directly deduced from measurements on two samples. If the sample is hysteretic like an elastic plastic material, there is not a unique solution to the flow and a separate drive measurement is needed. Time-dependent plasticity (spall in aluminum or twinning in U6Nb) has parabolic equations and backward solutions are unstable. Analyses that compare experiment and simulation have very broad minima in the parameters used to model stress-strain; unconstrained polynomial stress-strain expansions can wander and converge to unreasonable results. Better convergence is achieved with constrained models like certain forms of the Mie-Gruneisen EOS (copper to 18GPa) but those poorly represent materials with large changes in compressibility with strain (HMX to 50GPa). Maintaining small sample thickness to eliminate shock-up while maximizing thickness for accurate wave velocity measurement produces problems for designing high stress experiments and leads to hybrid experimental designs. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, March 14, 2006 11:51AM - 12:27PM |
H42.00002: From solitons to shocks: entropy generation and quasi-isentropic compression Invited Speaker: Recently a number of experimental platforms have demonstrated the ability to produce stress waves that have thermodynamic paths intermediate between an ideal isentrope and the Hugoniot. It is of interest to quantify the entropy generated for a given path in order to accurately determine the equation of state. Stationary propagating structures known as solitons have recently been observed in particle velocity time histories and provide insight as to how entropy is generated in quasi-isentropic flows. The origin of the structures is discussed in terms of dispersion and dissipation and a metric for quantifying the entropy generated is derived. A generalization of Lagrangian analysis is presented that allows an experimental determination of the relative contributions of nonlinear steepening, dispersion and dissipation. Finally, wavelet analysis is introduced as a powerful tool for the quantification of nonlinear wave dispersion and energy dissipation. [Preview Abstract] |
Tuesday, March 14, 2006 12:27PM - 12:39PM |
H42.00003: Application of Ellipsometry to Shock-Compressed Materials J. Reed Patterson, Jeffrey H. Nguyen, Neil C. Holmes \noindent Measurements of optical properties, such as the dielectric tensor, along the shock Hugoniot can be achieved in real time and {\em{in-situ}} via ellipsometry. Since standard Hugoniot-EOS and sound speed experiments do not provide crystal structure information, our knowledge of the phase diagrams of high-pressure high-temperature materials is limited. Complementary to x-ray diffraction techniques, ellipsometry of dynamically compressed materials provides data that can be coupled with calculations, yielding information on phase transitions and crystal structures. Single-wavelength ellipsometry experiments demonstrate our ability to observe solid-solid ($\alpha-Fe\to \epsilon-Fe$) and solid-liquid (e.g. Sn) phase transitions. In addition, changes in the complex index of refraction are related to changes in the strain state of a material, as observed in preliminary experiments on LiF, which demonstrated stress-incduced birefringence. Time-resolved ellipsometric measurements have the potential to provide insight into dynamic phenomena such as elastic/plastic deformation/relaxation and phase transition kinetics. We will also discuss our efforts to extend the applicability of ellipsometry of dynamically compressed materials by incorporating multiple wavelengths. [Preview Abstract] |
Tuesday, March 14, 2006 12:39PM - 12:51PM |
H42.00004: Experimental Measurement of Compression Isentropes to Multimegabar Pressures Jean-Paul Davis Isentropic ramp-wave loading of condensed matter has been hailed as a potential means to obtain accurate equation-of-state (EOS) data in the solid phase at relatively low temperatures and multimegabar pressures. In this range of pressure, isothermal diamond-anvil techniques have limited accuracy due to reliance on theoretical EOS of calibration standards; accurate isentropic compression data would help immensely in constraining EOS models. An isentropic compression technique developed using the Z Machine at Sandia as a magnetic drive has been extended to the multimegabar regime. Diagnostics typically consist of time-resolved velocity interferometry to monitor the back surfaces of samples having different thickness but subjected to the same magnetic loading. A number of design and analysis issues arise when attempting to extract a stress-density curve from such data. Following a brief discussion of these issues, recent results will be presented for quasi-isentropic compression of several materials to greater than 200 GPa. [Preview Abstract] |
Tuesday, March 14, 2006 12:51PM - 1:03PM |
H42.00005: Recent Advances in Tailored Dynamic Compression Jeffrey H. Nguyen, Jeremy R. Patterson, Daniel Orlikowski, Louis P. Martin, P. Asoka-Kumar, Klaus Widmann, Neil C. Holmes In the past few years, the functionally graded density impactor has been used in dynamic compression experiments that are tailored to reach previously inaccessible dynamic thermodynamic states beyond the principal Hugoniot and isentrope. These experiments demonstrated complex loading paths that included a combination of shocks, quasi-isentropic compressions, and controlled releases. The quasi-isentropic compression experiments last microseconds, and are capable of bridging the timescales of static experiments and current dynamic compression experiments. Some of the interesting experiments that were carried out included phase transition and equation of state studies. Our recent efforts have been concentrated on improving reproducibility and planarity of the impactors. Here, we will report the efforts and progresses on impactor manufacturing as well as experiments characterizing these impactors. We employed both line-VISAR and multi-PDV probes to characterize the planarity of the impactor as the target undergoes tailored dynamic compression. [Preview Abstract] |
Tuesday, March 14, 2006 1:03PM - 1:15PM |
H42.00006: Dynamic Response of Shock-Loaded Multi-Component Glasses C.S. Alexander, W.D. Reinhart, T.J. Vogler, D.E. Grady, L.C. Chhabildas Glass, in various formulations, may be useful as a transparent armor material. Fused quartz (SiO$_{2})$, modified with either B$_{2}$O$_{3}$ (13 {\%} wt.) or Na$_{2}$O (15 {\%} wt.), was studied to determine the effect on the dynamic response of the material. Utilizing powder and two-stage light gas guns, plate impact experiments were conducted to determine the effect on strength properties, including the elastic limits and plastic deformation response. Further, the effect of glass modification on known transitions to higher density phases in fused quartz was evaluated. Results of these experiments will be presented and discussed. [Preview Abstract] |
Tuesday, March 14, 2006 1:15PM - 1:27PM |
H42.00007: Coherent optical photons from shock waves in polarizable crystals Evan Reed, Marin Soljacic, Richard Gee, John Joannopoulos We predict that coherent electromagnetic radiation can be generated in polarizable crystalline materials when subject to a shock wave or soliton-like propagating excitation. To our knowledge, this phenomenon represents a new source of coherent optical radiation source in the 1-100 THz frequency range that is distinct from lasers and free-electron lasers. The radiation is generated by the synchronized motion of large numbers of atoms when a shock wave propagates through a crystal. Analytical theory, finite-difference time-domain simulations of Maxwell's equations, and molecular dynamics simulations demonstrate coherence lengths on the order of mm (at 16 THz) and potentially greater. [Preview Abstract] |
Tuesday, March 14, 2006 1:27PM - 1:39PM |
H42.00008: kinetics of solid to solid phase transitions in bismuth Ricky Chau, Frederick Streitz The role of kinetics in determining the time scale for transition from one phase to another is not known, but has been cited as contributing to the often observed discrepancy between phase boundaries determined in dynamic versus static pressure experiments. In this study, we demonstrate the use of real-time electrical conductivity as a phase diagnostic by presenting preliminary measurements of the conductivity of Bi under dynamic loading conditions. By exploiting the drastic variation in electrical conductivies among the low pressure phases, we are able to correlate changes in measured conductivity with phase changes in the sample. We will discuss the observed timescale for the phase transitions as well as possible effects due to the competition of phases. In addition, we will present results from experiments where both the electrical conductivity and particle velocity profiles are measured simultaneously, allowing observation of both the bulk and the local response of the system. \\\\ This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Tuesday, March 14, 2006 1:39PM - 1:51PM |
H42.00009: Pressure Induced Metallization of Light Group IV Hydrides Aitor Bergara, Miguel Martinez-Canales, Ji Feng, Wojciech Grochala, Roald Hoffmann, N.W. Ashcroft Recently reported superconductivity in lithium under pressure has renewed the interest on hydrogen and hydrogen-rich systems in the long standing conquest of room temperature superconductivity. Although the required metallization of pure hydrogen cannot be achieved within current experimental capabilities, chemical precompression exerted by heavier atoms in compounds with a large hydrogen content is expected to imply that lower pressures might be required to attain the metallic transition in these alloys. In this work we present an \textit{ab initio} analysis of pressure induced metallization of methane, silane and germane, as light group IVa hydrides. According to our calculations, although metallization in methane cannot be reached at pressures lower than 400 GPa, silane and germane are predicted to become metallic at experimentally accessible pressures of around 90 GPa and 70 GPa, respectively. Possible superconducting transitions of these compounds will be also analyzed. [Preview Abstract] |
Tuesday, March 14, 2006 1:51PM - 2:03PM |
H42.00010: Core/Shell Nanocrystalline Clusters in a Glass Matrix: A High Pressure Synchrotron X-Ray Diffraction Study Patricia E. Kalita, Gino Mariotto, Yoshimichi Ohki, Kristina E. Lipinska-Kalita Synchrotron x-ray diffraction studies up to 50 GPa were performed on an optically transparent composite with nanometer-sized ZrTiO$_{4}$/LiAlSi$_{2}$O$_{6}$ core/shell clusters embedded in a host glass. In the low-pressure range the shift and broadening of the x-ray diffraction lines was consistent with the densification of the LiAlSi$_{2}$O$_{6}$ shell phase. At higher pressures, the considerable diffraction line broadening pointed to a partial amorphization of the nanocrystalline phase. With pressure increase the x-ray patterns progressively revealed the presence of the ZrTiO$_{4}$ core phase. Upon decompression from 50 GPa to ambient conditions the pressure-induced changes were not fully reversible, however the diffraction pattern of the pressure-quenched material suggested that the decompressed structure carries the signature of the initial ambient LiAlSi$_{2}$O$_{6}$ phase. [Preview Abstract] |
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