Alumina-filled epoxies are composites having constituents with highly dissimilar mechanical properties. Complex behavior during shock compression and release can result, particularly at higher alumina loadings. In the current study, a particular material containing 43% alumina by volume was examined in planar-impact experiments. Laser interferometry was used to measure particle velocity histories in both reverse-impact and transmitted-wave configurations. Hugoniot states and release-wave velocities were obtained at shock stresses up to 10GPa, and represented smooth extensions of previous data at lower stresses. Surprisingly high release-wave velocities continued to be the most notable feature. Measured profiles of transmitted waves show a gradual transition from viscoelastic behavior at high shock stresses to a more complex behavior at lower stresses in which viscous mechanisms produce a broadened wave structure. This wave structure was examined in some detail for peak stress dependence, evolution towards steady-wave conditions, and initial temperature effects.

Shock wave compression of poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (PZT 95/5-2Nb) results in rapid depoling and release of bound charge. In the current study, planar-impact experiments with this material were conducted on a gas-gun facility to determine Hugoniot states, to examine constitutive mechanical properties during shock propagation, and to investigate shock-induced depoling characteristics. A previous article summarized results from the first two of these areas, and this article summarizes the depoling studies. A baseline material, similar to materials used in previous studies, was examined in detail. More limited experiments were conducted with other materials to investigate the effects of different porous microstructures. Experiments were conducted over a wide range of conditions in order to examine the effects of varying shock strength, poling orientation, input wave shape, electric field strength, porous microstructure at a fixed density, and initial density. Depoling currents were recorded in an external circuit under either short-circuit or high-field conditions, and provide a convenient means of examining the kinetics associated with the ferroelectric–to–antiferroelectric phase transition. For sufficiently strong shock waves, the measured short-circuit currents indicate that the phase transition is very rapid and essentially complete. As shock strengths are reduced, short-circuit currents show increasing rise times and decreasing final levels at the end of shock transit. These features indicate that the transition kinetics can be characterized in terms of both a transition rate and a limiting degree of transition achieved in a given shock experiment. The presence of a strong electric field does not appear to have a significant effect on transition kinetics at high shock stresses, but has a strong effect at low stresses. As was found for constitutive mechanical properties, only small effects on measured currents resulted from differences in the porous microstructure of common-density materials, but large effects were observed when initial density was varied. To examine transition kinetics in more detail, short-circuit currents obtained with the baseline material and several approximate methods were used to estimate values for the rate and degree of transition as functions of shock properties. Differences between these currents and currents measured in high-field experiments using the same impact conditions were used to examine field effects on transition kinetics and corresponding dielectric properties.

Explicit relations between index of refraction and density are obtained for shock-compressed fused silica and sapphire. The relations are derived from the Doppler-frequency corrections to velocity-interferometry data obtained by Barker and Hollenbach in plate-impact experiments. The index-density relation for sapphire was found using an expression for the Doppler-frequency shift produced by a window material experiencing shock compression. For fused silica, a numerical calculation was required to compute frequency corrections for the combined ramp/shock waveforms produced in the experiments. In both cases the behavior of the refractive index over the density range of the data was found to be predicted quite accurately by adding a correction term to the Gladstone-Dale relation. A particular power-law dependence on density was found for this correction term in each case. The explicit index-density relations permit detailed calculations to be made for index-of-refraction effects from window materials in plate-impact experiments using velocity interferometry. As an example, refractive-index effects are calculated for a fused silica window experiencing a slowly rising compression wave generated in a glass-ceramic material. The present results also permit the polarizability behavior of these materials under shock compression to be examined.

Although the particular lead zirconate/titanate composition Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (PZT 95/5–2Nb) was identified many years ago as a promising ferroelectric ceramic for use in shock-driven pulsed power supplies, relatively few studies have been performed to characterize its response under shock wave compression. The current study began when strong interest developed in numerically simulating the operation of pulsed power supplies, which required improved models for dynamic material properties. Experiments were conducted on a gas-gun facility to determine Hugoniot states, to examine constitutive mechanical properties during shock propagation, and to investigate shock-driven depoling kinetics. This article summarizes results from the first two of these areas. A baseline material, similar to materials used in previous studies, was examined in detail. Limited experiments were conducted with other materials to investigate the effects of different porous microstructures. Reverse-impact experiments were used to obtain a Hugoniot curve for the baseline material over the stress range of interest, as well as comparative data for the other materials. Wave profiles recorded in transmitted-wave experiments examined the effects of varying shock strength and propagation distance, poling state and orientation, initial density, porous microstructure at a fixed density, and electric field strength. The collective results identify a complex material behavior governed by anomalous compressibility and incomplete phase transformation at low shock amplitudes, and a relatively slow yielding process at high shock amplitudes. Differences in poling state, field strength, and porous microstructure in common-density materials were found to have a small effect on this behavior, but large effects were observed when initial density was varied. Comparisons with similar studies on other ceramic materials show both similarities and differences, and provide insights into possible yielding mechanisms.

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