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 P3: Phase Transitions III |
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Chair: Jeff Nguyen, Lawrence Livermore National Laboratory Room: Fairmont Orchid Hotel Plaza I |
Thursday, June 28, 2007 10:30AM - 10:45AM |
P3.00001: Electronic Conduction of Tin Under High Pressure from A phenomenological Equation of State. Shlomi Pistinner Phase transition under shock loading, and unloading are indirectly inferred from an abrupt change in the speed of sound . To estimate this change we use the Tin thermodynamic-phenomenological equation of state, obtained by Mabire and Heril (SCCM 2000). Mabire and Heril have demonstrated the ability of this equation of state to reproduce VISAR profiles obtained in impact experiments. The parameters of this equation of state are worked out in the frame work of Debye theory and converted to parameters usable in the Bloch-Grueisen $\vert $DC resistivity formula. This quantity is then used in Drude AC resistivity model to infer a wavelength dependent emissivity. The emissivity so inferred can be used to reduce uncertainties in temperature which is inferred from pirometric measurements at shocked Tin unloading. This can be done in a manner consistent with the probed equation of state. In principle the prediction of the exercise carried out below are verifiable via independent measurements of an angle dependent emissivity via techniques such as ellipsometry. [Preview Abstract] |
Thursday, June 28, 2007 10:45AM - 11:00AM |
P3.00002: Free Surface Temperature Measurements on Shock loaded Tin (Melting on Release) Achim Seifter, Andrew Obst, David Holtkamp, Dale Turley, Mike Furlanetto, Jeremy Payton, Carl Greeff Theory predicts that over a certain range of Hugoniot pressures the free surface temperature of shock loaded tin is the ambient pressure melting temperature of 505K. In a series of high explosive driven (direct drive) shocks into tin of various thicknesses we attempted to measure this constant temperature. From the lower end (195kbar) up to the middle (250kbar) of this pressure range we could observe this temperature within the uncertainty of our measurements. From about 250kbar up to the higher end (330kbar) the measured free surface temperature was increasing with increasing Hugoniot pressure. In this paper we will describe the experimental setup, the diagnostic systems (pyrometry and Photon Doppler Velocimetry) and give possible explanations for the temperature readings higher than the predicted 505K in the upper half of the investigated pressure range. [Preview Abstract] |
Thursday, June 28, 2007 11:00AM - 11:15AM |
P3.00003: Measurements of the Dynamic $\beta$--$\gamma$ Phase Boundary in Tin Jean-Paul Davis, Dennis B. Hayes Experiments performed on the Z machine at Sandia Labs used magnetically generated planar ramp waves to quasi-isentropically compress pre-heated solid tin across the equilibrium $\beta$--$\gamma$ phase boundary. Velocity history measurements at a tin/window interface exhibited features that could be consistently related, through simulations, to the $\beta$--$\gamma$ structural transformation occurring in the bulk tin. The simulations used a homogeneous phase-mixture model with a $\gamma$-phase energy offset that was adjusted to match the measured velocity feature. This determined the phase-boundary pressure from experiment and the phase-boundary temperature from the $\beta$-phase equation of state. Due to wave interactions, measurements using sapphire windows were more difficult to interpret than those using LiF windows and thus led to results with larger uncertainty. The measured phase boundary pressure did not depend on the tin's initial microstructure, nor on perturbations to the wave profile arising from the difficulty of pre-heating a soft metal in the isentropic compression configuration. [Preview Abstract] |
Thursday, June 28, 2007 11:15AM - 11:30AM |
P3.00004: Atomistic Simulations of Shock Waves in Polycrystalline Iron Compared to Experiments Kai Kadau, T.C. Germann, P.S. Lomdahl, R.C. Albers, J.S. Wark, A. Higginbotham, B.L. Holian The propagation of shock waves through a polycrystalline iron sample is explored by large-scale atomistic simulations. For large enough shock strengths the passage of the wave causes the body-centered-cubic (bcc) structure to transform into a close-packed structure with most structure being isotropic hexagonal-close-packed (hcp) and, depending on shock strength and grain orientation, some fraction of face-centered-cubic (fcc) structure. The simulated shock state as represented by the Hugoniot is compared to experimental data. By calculating the extended x-ray absorption fine structure (EXAFS) directly from the atomic configurations obtained by our simulations, a comparison to recent experimental EXAFS measurements of nanosecond-laser shocks in polycrystalline iron shows that the experimental data is consistent with a phase transformation. However, the atomistically simulated EXAFS spectra also show that an experimental distinction between a product hcp or fcc phase is not possible based on the EXAFS spectra alone. [Preview Abstract] |
Thursday, June 28, 2007 11:30AM - 11:45AM |
P3.00005: Recovery Studies of Shocked Iron Single Crystals Bassem El-Dasher, Nathan Barton, Warren MoberlyChan, James McNaney, James Hawreliak, Hector Lorenzana Time resolved, in-situ X-Ray diffraction measurements indicate that the bcc-hcp transition in single crystal iron occurs at about 13 GPa. These results also show that the high pressure phase is a polycrystal with two variants. Further studies on the recovered specimens using transmission electron microscopy show that these shocked samples surprisingly reverse transform from a high pressure polycrystal to the original single crystal structure upon release. These results will be discussed in the context of the time resolved data and theoretically based transformation pathways. [Preview Abstract] |
Thursday, June 28, 2007 11:45AM - 12:00PM |
P3.00006: ABSTRACT WITHDRAWN |
Thursday, June 28, 2007 12:00PM - 12:15PM |
P3.00007: Effect of nano-void on the phase transformation of single crystal iron under shock compression Xinlin Cui, Wenjun Zhu, Hongliang He, Yingjun Li Shock-induced phase transformation (body-centered cubic $\alpha $ phase to hexagonal close-packed $\varepsilon $ phase) in single crystal iron has been investigated by means of the molecular dynamics (MD) simulation using an embedded atom method (EAM) potential. By introducing a nano-void in the single crystal iron, the nucleation velocity and the nucleation sites are observed to be different from the ideal single crystal iron. The simulation results show that the void accelerates the nucleation velocity, which induces the new phase to nucleate easier. At the same time, the void affects the nucleation sites, the initial homogeneous nucleation is observed near to the leading front of the shock wave in the ideal single crystal iron, but they firstly occur around the edge of the void, and finally form a butterfly shaped transformation zone in the defect single crystal iron. By calculating the distribution of the resolved shear stress along the slip plane, the reason why the nucleation sites are different has been explained. [Preview Abstract] |
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