Robert E. Setchell

Shock wave compression of the ferroelectric ceramic Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3: Depoling currents

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 a...

Index of refraction of shock‐compressed fused silica and sapphire

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 plat...

Shock wave compression of the ferroelectric ceramic Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3: Hugoniot states and constitutive mechanical properties

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 wer...

Refractive index of sapphire at 532 nm under shock compression and release

The refractive index of sapphire at 532 nm has been determined along the Z axis over a range of conditions produced in shock compression and release experiments. In these experiments, a laser interferometer is used to measure particle velocity at an interface with a sapphire window. Values for refractive index are found from velocity corrections that must be made to account for refractive-index changes in the window due to shock wave motion. Early studies found that Z-cut sapphire windows resulted in much larger corrections than other window materials. These studies examined refractive-index changes at a wavelength of 633 nm, corresponding to the helium-neon lasers typically used in interferometers at that time. Because of the high shock impedance of sapphire, its use as an interferometer window since the early studies has been limited. Recent interest in the shock response of high-impedance ceramics, however, has resulted in considerable use of sapphire windows in experiments using laser interferometers ...

Shock wave compression of the ferroelectric ceramic Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3: Microstructural effects

Shock wave compression of poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 results in rapid depoling and release of bound charge. Different porous microstructures can be produced in the material by adding different types and amounts of organic pore formers prior to bisque firing and sintering. In previous studies, extensive planar-impact experiments on a baseline material having a fixed porous microstructure were conducted to determine Hugoniot states, to examine constitutive mechanical properties during shock propagation, and to investigate shock-induced depoling characteristics. Additional comparative experiments were conducted to investigate the effects of a different porous microstructure in a material having the same density, and also the effects of different initial densities. These comparisons indicated that differences in the porous microstructure of common-density materials have little effect on mechanical and electrical shock properties, in contrast to large effects observed when initial density is varied...

Shock-compression response of an alumina-filled epoxy

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...

Compositional effects on the shock-compression response of alumina-filled epoxy

Alumina-filled epoxies are composites having constituents with highly dissimilar mechanical properties, resulting in complex behavior during shock compression and release. A previous study examined the shock properties of a particular composition in some detail. In the current study, the effects of compositional variations on shock properties were examined. Planar-impact experiments producing states of nearly equal strain were conducted to investigate the effects of changes in the size and shape of alumina particles, and in the total volume fraction of alumina. Laser interferometry and wave timing were used to obtain transmitted wave profiles, Hugoniot states, and release wave velocities. In addition, wave profiles and velocities were obtained in “thin-pulse” experiments that examined the combined effects of compression and release properties in different compositions. Changes in the size and shape of alumina particles were found to have little effect except in the viscous spreading of wave profiles durin...

Raman scattering measurements of nitric oxide in ammonia/oxygen flames

Abstract Local measurements of temperature and the concentrations of nitric oxide, oxygen, and nitrogen are obtained in lean ammonia/oxygen flat flames using Raman spectroscopy. The data show that super equilibrium levels of nitric oxide are produced, and that nitric oxide destruction processes are rapidly quenched in the post flames gases.

Effects of precursor waves in shock initiation of granular explosives

Abstract The effects of compressive waves propagating ahead of stronger shock waves in a granular explosive have been investigated experimentally. In particular, the propagation and growth of 5.0 GPa shocks preceded by either a 3.2 GPa shock or a 2.0 GPa ramp wave having a 0.6 μs rise time were examined in the low porosity explosive PBX-9404. The evolution of a 3.5 GPa shock preceded by a 0.2 GPa precursor wave was also examined in this explosive. The initial waves were generated using planar impact techniques, and laser velocity interferometry (VISAR) was used to measure particle velocity histories after the waves had propagated through explosive samples having different thicknesses. The recorded waveforms for shocks with precursors were compared with similar measurements obtained for single shocks having the same peak axial stresses. These comparisons confirmed that compression by a precursor wave renders the granular explosive less sensitive to initiation by a subsequent shock. For the 5.0 GPa cases, the ramp wave precursor was more effective in retarding the release of chemical energy than the precursor shock. In both cases the propagation distance required to achieve detonation was extended by an amount that depended on the duration of the precursor. The 0.2 GPa precursor was also found to be quite effective in desensitizing the PBX-9404 to the subsequent 3.5 GPa shock. This suggests that desensitization can result from precursor waves just strong enough to reduce the porous microstructure within the granular material.

Dielectric Properties of PZT 95/5 during Shock Compression under High Electric Fields

Shock‐induced depoling of the ferroelectric ceramic PZT 95/5 is utilized in pulsed power devices. High electric fields are generated within a normally poled ceramic element when the depoling current is passed through a large load resistor. Under these conditions, a portion of the depoling current is retained on the element electrodes to account for capacitance. This effect is governed by the dielectric properties of both unshocked and shocked PZT 95/5 as the field develops during shock transit. Previous studies proposed either constant or relatively simple relaxing behavior for dielectric properties on either side of the shock front. However, interpretation of the corresponding experiments was complicated by possible field effects on depoling kinetics. Recent studies have used different experimental configurations to better isolate the dielectric behavior. Multiple PZT 95/5 elements are displaced both parallel and perpendicular to the direction of shock motion to allow for sequential charging of unshocked...