Publications

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Of special promise for providing dynamic mesoscale response data is the line-imaging VISAR, an instrument for providing spatially resolved velocity histories in dynamic experiments. We have prepared two line-imaging VISAR systems capable of spatial resolution in the 10-20 micron range, at the Z and STAR facilities. We have applied this instrument to selected experiments on a compressed gas gun, chosen to provide initial data for several problems of interest, including: (1) pore-collapse in copper (two variations: 70 micron diameter hole in single-crystal copper) and (2) response of a welded joint in dissimilar materials (Ta, Nb) to ramp loading relative to that of a compression joint. The instrument is capable of resolving details such as the volume and collapse history of a collapsing isolated pore.

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Recently an innovative technique known as the Isentropic Compression Experiment (ICE) was developed that allows the dynamic compressibility curve of a material to be measured in a single experiment. Hence, ICE significantly reduces the cost and time required for generating and validating theoretical models of dynamic material response. ICE has been successfully demonstrated on several materials using the 20 MA Z accelerator, resulting in a large demand for its use. The present project has demonstrated its use on another accelerator, Saturn. In the course of this study, Saturn was tailored to produce a satisfactory drive time structure, and instrumented to produce velocity data. Pressure limits are observed to be approximately 10-15 GPa (''LP'' configuration) or 40-50 GPa (''HP'' configuration), depending on sample material. Drive reproducibility (panel to panel within a shot and between shots) is adequate for useful experimentation, but alignment fixturing problems make it difficult to achieve the same precision as is possible at Z. Other highlights included the useful comparison of slightly different PZT and ALOX compositions (neutron generator materials), temperature measurement using optical pyrometry, and the development of a new technique for preheating samples. 28 ICE tests have been conducted at Saturn to date, including the experiments described herein.

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Two experiments have been performed to measure the effects of pulsed radiation loads on the front of small tubular structures, using as an energy source the X-ray fluence produced by a Z-pinch at the Sandia National Laboratories Z Facility. The project had two major goals: to establish the feasibility of using the Z machine to study the phenomenology associated with debris generation and propagation down tubular structures with partitions; and to use the resultant experimental data to validate numerical hydrocodes (shock physics codes) so that we have confidence in their use in analyzing these types of situations. Two tubular aluminum structures (5 and 10 cm long and 1 cm inside diameter) were prepared, with aluminum partitions located at the front, halfway down the pipe, and at the rear. Interferometry (VISARs) provided multiple velocity histories for all of the partitions. In both experiments, the first barrier, which was exposed directly to the x-ray fluence, was launched into the pipe at a velocity of ∼2 km/s, accelerating to give a mean velocity of ∼ 2.6 km/s. Loss of plate integrity is inferred from the dispersed launch of the second partition at ∼1 km/s. Wall shocks propagating at 4.5 km/s were inferred. Post-test metallography showed evidence of melting and partial vaporization of the plates, and turbulent mixing with material from the walls. Calculations qualitatively agree with the observed results, but slightly overpredict debris velocity, possibly due to overestimates of total energy fluence. An application for this work is the study of techniques for line-of-sight shock and debris mitigation on high-power pulsed power facilities such as Z and its follow-on machines. © 2001 Elsevier Science Ltd. All rights reserved.

In the present study, 10 impact tests were conducted on unpoled PZT 95/5, with 9% porosity and 2 at% Nb doping. These tests were instrumented to obtain time-resolved loading, unloading and span signatures. As well, PVDF gauges allowed shock timing to be established explicitly. The ferroelectric/antiferroelectric phases transition was manifested as a ramp to 0.4 GPa. The onset of crushup produced the most visible signature: a clear wave separation at 2.2 GPa followed by a highly dispersive wave. The end states also reflected crushup, and are consistent with earlier data and with related poled experiments. A span strength value of 0.17 GPa was measured for a shock stress of 0.5 GPa, this decreased to a very small value (no visible pullback signature) for a shock strength of 1.85 GPa.