Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session J3: Experimental Developments I |
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Chair: Paulo Rigg, Los Alamos National Laboratory Room: Hyatt Regency Constellation D |
Tuesday, August 2, 2005 11:00AM - 11:15AM |
J3.00001: X-ray microtomography of sugar and HMX granular beds undergoing compaction Martin Greenaway Granular beds are an important simulant of damaged PBXs which have developed porosity. Recent developments in X-ray microtomography have provided us with the ability to resolve energetic crystals contained within a polymer matrix or granular bed. Although electron microscopy offers better spatial resolution, it yields little information beyond the surface. Methods to look inside a granular bed, PBX or energetic crystal involving polishing or optical microscopy have enjoyed only limited success. The information now available using X-ray microtomography surpasses these methods, as will be shown in this paper. Two-dimensional slices through a sample are obtained and can be reconstructed to form a three-dimensional image of the entire bed. Slices through energetic crystals reveal the presence of intragranular pores. Granular beds of sugar and HMX have been subjected to various compaction experiments; fracture, bed rearrangement, changes in porosity and other affects are clearly visible and quantifiable. The extent of bed fracture makes it possible to approximate the extent of energy dissipation due to material fracture over the different compaction regimes. [Preview Abstract] |
Tuesday, August 2, 2005 11:15AM - 11:30AM |
J3.00002: Three-dimensional Dynamic Deformation Measurements using Stereoscopic Imaging and Digital Speckle Photography Helen Prentice, Martin Greenaway, William Proud A technique has been developed in order to determine experimentally the three-dimensional displacement field on the rear surface of a dynamically deforming plate. The technique combines speckle analysis with stereoscopy, using a modified translated-lens method: this allows split-frame photography, increased image resolution and a larger effective lens separation in order to increase image disparity and reduce errors in the shape reconstruction. Whilst several analytical models exist to predict deformation in extended or semi-infinite targets, the non-trivial nature of the wave interactions complicates the generation and development of analytical models for targets with significantly finite depth. By interrogating specimens experimentally to acquire three-dimensional strain data points, both analytical and numerical model predictions can be verified more rigorously. The technique is applied to the quasi-static deformation of a rubber sheet and dynamically to sheets of Copper and Mild Steel of various thicknesses. [Preview Abstract] |
Tuesday, August 2, 2005 11:30AM - 11:45AM |
J3.00003: Streaked Optical Pyrometer for Shock-Wave and EOS Studies J.E. Miller, T.R. Boehly, E. Vianello, W. Armstrong, C. Sorce, W. Theobald, D.D. Meyerhofer, D.G. Hicks, J.H. Eggert, P.M. Celliers The optical self-emission from laser-driven shock waves provides important information about the strength of a shock and the equation of state of the shocked material. A streak camera was used to temporally and spatially resolve emission from transparent targets. A NIST-traceable lamp was used to calibrate the device to provide brightness temperatures. Various shock-timing and EOS experiments demonstrate the relationship between shock velocity (strength) and optical emission. The coalescence of two shocks and their arrival at the rear surface are observed, providing valuable shock-timing data. Temperature measurements in $\alpha $-quartz samples are used to evaluate various EOS models. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460, the University of Rochester, and the New York State Energy Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article. [Preview Abstract] |
Tuesday, August 2, 2005 11:45AM - 12:00PM |
J3.00004: Temporal profiles of explosively-generated pressures in solids measured by an optical fiber-based gauge Jeremy Monat, Joel Carney, V. Whitley, G. Pangilinan A new gauge is being developed and calibrated to measure pressures generated from explosives as a function of time in solids where traditional gauges are not applicable. A laser-pumped optical fiber-based gauge was embedded in Modified Gap Test cylinders. The gauge responded to pressure and showed other features likely due to additional interfaces beyond the fiber tip. Since the temporal profile of the pressure is not well known, hydrocode and ray-tracing modeling are being used to understand the results. The gauge shows promise for time-resolving explosively-generated shock pressures in solids. [Preview Abstract] |
Tuesday, August 2, 2005 12:00PM - 12:30PM |
J3.00005: Single-shot real-time spectroscopy of permanent structural and chemical change in solids Invited Speaker: Time-resolved measurements of solid samples in the process of irreversible change pose special challenges since the common practices of signal averaging and measurement repetition with different temporal delays or windows are often impractical. Ideally, the entire time-dependent sample response can be recorded in real time, during a single event. Here we present two types of time-resolved measurements of solid-state structural and chemical evolution that are conducted in real time, on a single-measurement basis. The first is femtosecond time-resolved transient absorption or reflection spectroscopy, using a single excitation laser pulse and 400 distinct probe pulses with different temporal delays. Real-time measurements of ultrafast, permanent structural and chemical rearrangements in semimetals, semiconductors, and organic molecular crystals have been conducted using this method, which is based on the use of orthogonally oriented stairstep ``echelon'' elements to split an incident probe beam into a 20 x 20 array of spatially and temporally distinct pulses that are passed through the sample and then imaged onto a CCD camera for data extraction. The second measurement, conducted on a single-shot basis using a GHz-bandwidth photodetector and oscilloscope for nanosecond time resolution, involves optically generated and monitored acoustic waves whose properties reveal the mechanical state of a sample. Both of these measurements are of particular interest in the case of shock loading. Measurements on samples under laser or gas gun driven shock loading will be discussed. [Preview Abstract] |
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