Table of contents

Shock compression and impact studies could benefit from the ability to increase impact velocities that can be achieved with gun systems. Single-stage guns have modest performance (0.2-2 km/s) that limits their utility for high-pressure and high-velocity studies, while more capable systems are expensive and complex. We are developing a technique that uses a low-strength sabot with a tapered die to increase the impact velocity without modifying the gun itself. Impact of the projectile with the die generates a converging shock wave in the sabot that acts to accelerate the front of the projectile, while decelerating the rear portion. Preliminary experiments using this technique have observed a velocity enhancement of up to a factor of two.

We developed a simple magnetic gauge for measuring free surface velocities of rock materials in the range of 0.1-20 m/s. The gauge consists of two elements: a NdFeB magnet and a pick-up coil. The coil is attached to the free surface at the point of interest. The magnet is placed a few centimeters away from the coil and the rock. The motion of the rock surface, due to blast loading, induces current in the coil due to the changes in the magnetic flux. The coil velocity is deduced from the measured current using a computational code. The gauge was tested and validated in a set of free-falling experiments. We present velocity measurements from various blast experiments in limestone and reinforced concrete, using both the magnetic gauge and a Doppler interferometer. The results obtained from the two measurement techniques are in good agreement. Since the magnetic gauge is cheap and very simple to operate, it is well-suited for mapping the velocity distribution at multiple points of interest on the concrete surface.

We have established a new type of experimental set-up utilizing a Paris-Edinburgh (PE) type large volume press with a dedicated sample cell assembly for simultaneous x-ray diffraction, electrical resistance, and temperature gradient measurements at the High-Pressure Collaborative Access Team (HPCAT) at Advanced Photon Source (APS), Argonne National Laboratory 16BM-B beamline. We demonstrate the feasibility of performing in situ measurements and correlating the measured electrical-thermal-structural properties over a broad range of P-T conditions by observing the well-known solid-solid and solid-melt transitions of bismuth (Bi) up to 5 GPa and 600° C. The goal of developing this new multi-probe measurement capability is to further improve detection of the onset of solid-solid and solid-melt transitions, relate structural and electrical properties of materials, determine changes in thermal conductivity at high P-T, and ultimately extend the technique for investigating other parameters, such as the Seebeck coefficient of thermoelectric materials.

Progress towards probing molecular dynamics of octahydro-1,3,5,7-tetranitro-1,3,4,7-tetrazocine (HMX) subjected to shock compression of a few GPa and/or temperature excursions exceeding thermal decomposition values (T > 500 K) is described. Due to shock velocities of a few nm/ps, nanometer-thick layers are needed for picosecond time resolution. Therefore, 5-10 nm thick films of S-HMX were deposited on metallic substrates with a template of a 4-nitrobenzoic acid monolayer. A polymer layer a few microns thick was spin-coated on top of S-HMX for shock confinement. The monolayer and HMX layer were probed simultaneously utilizing an ultrafast nonlinear coherent vibrational spectroscopy, termed vibrational sum-frequency generation (SFG). Shock pressures were estimated via comparisons with the monolayer nitro transition frequency blueshift in hydrostatic pressure measurements. Temperature determinations were made based on the reflectance of the metallic substrate.

Optical velocimetry is limited to measuring the component of the target velocity along the axis of the optical beam, thereby allowing a laterally moving tilted surface to approach a probe undetected. We are not discussing the detection of the lateral motion, but rather the detection of material approaching the probe due to lateral motion of a surface that is not perpendicular to the beam. This motion is not measured in optical velocimetry, and consequentially, integrating the velocity will in general give an incorrect position. We will present three approaches to overcome this limitation: Tilted wave-front interferometry, which maps time of flight into fringe displacement; pulse bursts for which we measure the change in the average arrival time of a burst, and amplitude modulation interferometry, in which a change in path length shows up as a change in the phase of the modulation. All three of these have the potential to be integrated with existing velocimetry probes for simultaneous velocity and displacement measurements. We will also report on initial tests of these approaches.

We present recent time-resolved x-ray diffraction data obtained across the solidification of water to ice-VI and -VII at different compression rates. The structural evolution of ice-VI to ice-VII, however, is not a sharp transition, but occurs rather coarsely. The diffraction data shows an anisotropic compression behavior for ice VI; that is, the c-axis is more compressible than the a-axis at the same compression rate. Nevertheless, the present equations of state of both ice-VI and ice-VII obtained under dynamic loadings agree well with those previously obtained under static conditions. Hence, the present study demonstrates that time-resolved x-ray diffraction coupled with the dynamic-DAC is an effective method for investigating details of the structural response of materials over a wide range of well-controlled compression rates. Finally, we found the evidence for an X-ray induced chemical reaction of water and ice-VI. The impurities, produced by the x-ray induced chemical reaction, inhibit the formation of amorphous ice.

There is a requirement for off-Hugoniot data to validate material and equation of state models. One technique is to use projectiles with graded shock impedance layers in a gas gun to impact a target and apply a ramp loading. To accurately design a pressure profile to be applied to the target the impactor must be accurately characterised and modelled. Modelling also provides an assessment of whether lateral rarefactions will hinder the experiment, and increases confidence in the analysis of the results obtained. This paper considers several methods for calculating the equation of state of layered mixtures for application to the modelling of graded density impactors.

We report the measurement of the surface motion of a hemispherical copper shell driven by high explosives. This measurement was made using three 32 channel multiplexed photonic Doppler velocimetry (PDV) systems, in combination with a novel compound optical probe. Clearly visible are detailed features of the motion of the shell over time, enhanced by spatial correlation. Significant non-normal motion is apparent, and challenges in measuring such a geometry are discussed.

We have developed a Light Detection and Ranging (LIDAR) diagnostic to track the position of a projectile inside of a gas gun launch tube in real-time. This capability permits the generation of precisely timed trigger pulses useful for triggering high-latency diagnostics such as a flash lamp-pumped laser. An initial feasibility test was performed using a 72 mm bore diameter single-stage gas gun routinely used for dynamic research at Los Alamos. A 655 nm pulsed diode laser operating at a pulse repetition rate of 100 kHz was used to interrogate the position of the moving projectile in real-time. The position of the projectile in the gun barrel was tracked over a distance of ~ 3 meters prior to impact. The position record showed that the projectile moved at a velocity of 489 m/s prior to impacting the target. This velocity was in good agreement with independent measurements of the projectile velocity by photon Doppler velocimetry and timing of the passage of the projectile through optical marker beams positioned at the muzzle of the gun. The time-to-amplitude conversion electronics used enable the LIDAR data to be processed in real-time to generate trigger pulses at preset separations between the projectile and target.

In order to evaluate the behavior of a high power pulsed underwater electrical discharge, and especially characterize the pressure generated by such a discharge, we implemented several optical diagnostics. We first observed directly the expansion of the plasma produced by the dielectric breakdown of the water between the electrodes and the resulting gaseous pulsating bubble. This observation led to an estimate of the pressure inside the bubble with respect to time. We then visualized the propagation of the pressure wave generated by the discharge with shadowgraph and Schlieren setup. The obtained velocity was then used to evaluate the theoretical maximum pressure at the pressure front. Finally, we measured the velocity induced by the pressure wave on a thin aluminum disk with a heterodyne velocimeter and used numerical simulation to obtain a temporal form of pressure. These methods and results can be used to develop and assess performances of processes using underwater electrical discharges to generate pressure waves such as electrohydraulic forming.

A laser-driven mini flyer plate system, with 8 GHz photon Doppler velocimeter and high-speed spectroscopic diagnostics, was developed for shock compression spectroscopy. The properties of the flyer plate platform are discussed, and its use in two applications is reported. The two applications were impact initiation of nanotechnology reactive materials and molecular optical emission sensors to monitor mesoscale effects in a shock-compressed polymer.

We have recently demonstrated the use of nanophase Eu:Y₂O₃ and Eu:ZrO₂ as temperature sensors in explosions. Our previous measurements have shown that each of these materials is suitable for a certain temperature range – Eu:Y₂O₃ covers the range from about 500 K to about 900 K, and Eu:ZrO₂ the range from about 800 K to about 1300 K. In order to have one material that can cover a wider range of temperatures, we have prepared core/shell assemblies of these host materials with different dopants. Here we report on the synthesis and characterization of core/shell assemblies consisting of Er,Yb:ZrO₂ cores and Eu:Y₂O₃ shells. The Er,Yb:ZrO₂ core is synthesized via forced hydrolysis and the Eu:Y₂O₃ shell is synthesized via homogeneous precipitation. Subsequently, these core/shell assemblies are heated for 3 h in a furnace and for 10 s by a pyroprobe at various temperatures. Temperature-induced phase changes in the materials lead to changes in the optical spectra, which can then be correlated with temperature. The Er,Yb:ZrO₂ core emits upconverted light in the red and green spectral range when excited with 970 nm, while the Eu:Y₂O₃ shell emits in the red spectral range when excited with 532 nm. These spectra can be measured separately allowing us to determine temperatures over a wide range.

Two dimensional velocity interferometer (2d-VISAR) data can be treated as a kind of hologram, since fringes recorded by the interferometer manifest both phase and magnitude information about changes in the optical field of the target, over an image. By the laws of diffraction, knowledge of the optical field at one focal plane can be used to calculate the optical field at another focal plane. Hence a numerical re-focusing operation can be performed on the data post-experiment, which can bring into focus narrow features that were recorded in an out of focus configuration. Demonstration on shocked Si data is shown.

The results of four cylinder tests performed on two batches of the HMX based explosive EDC37 using a new suite of diagnostics are described. Heterodyne laser velocimetry (het-v) and pyrometry were fielded for the first time on cylinder tests within AWE. Pyrometry gave a measurement of the temperature of the detonating HE of 2600-3485 K. Sixteen channels of het-v were fielded and provided high fidelity expansion data at distances of up to 30 mm. High speed framing camera images were obtained and show no signs of cylinder break up or spallation until distances greater then 35 mm. The het-v expansion data made it possible to resolve up to 8 shock reverberations in the wall as it expands. The expansion of the cylinder wall was recorded both before and after steady state detonation was reached and the results compared. Het-v probes were fielded at different angles to the expanding cylinder wall allowing both the vertical and horizontal expansion velocity to be determined. The extra information that these cylinder tests yielded will allow for more accurate code validation and determination of the equation of state of the explosive products.

The Onionskin test has been the standard test to evaluate detonation wave breakout over a hemispherical surface for decades. It has been an effective test used in a variety of applications to qualify main charge materials, evaluate different boosters, and compare different detonators. It is not without its shortfalls however. It only images a small portion of the explosive and requires very precise alignment and camera requirements to make sense of the results. Asymmetry in explosive behavior cannot be pinpointed or evaluated effectively. We have developed a new diagnostic using fiber optics covering the surface of the explosive to yield a 3D representation of the detonation wave behavior. Precise timing mapping of the detonation over the hemispherical surface is generated which can be converted to detonation wave breakout behavior using Huygens' wave reconstruction. This report will include the results of a recent suite of tests on PBX 9501, and discussion of how the test was developed for this explosive and contrasting previous work on PBX 9502. The results of these tests will describe the effects on detonation wave breakout symmetry when Sylgard 184 is placed between the detonator and booster. The effects on symmetry and timing when the Sylgard gap thickness is increased and the detonator is canted will be shown.

A requirement exists to generate realistic insults in energetic targets, for example ramp loadings leading to shock waves. This paper examines the development of a ceramic flyer ramp wave generation technique. Ceramic stereolithography was used to produce fully-dense, graded areal density alumina ceramic flyers. These flyers consisted of multiple square pyramids arranged on a solid base. The gas gun plate impact and electromagnetic particle velocity gauge techniques were used to observe the ramp waves generated when the flyers impacted a Kel-F 81 polymer target. Ramp waves of varying properties were successfully generated in the targets, and good agreement was obtained with 3D hydrocode modelling.

A number of experiments were carried out using a modified version of the standard particle velocity gauge technique in plate impact experiments with inert targets. Unusually these utilised dynamic metallic elements. Traditional methodology advises against the use of metallic flyers/barriers with this technique as conductive objects moving in the magnetic field produce perturbations in the output gauge voltage leading to inaccuracies in the derived particle velocities. This body of work investigated the causes of the perturbation effect, methods of minimising its magnitude and possible post-processing correction methods. In experiments with Al flyers, perturbations on the order of 10-15% of signal strength were observed. While the magnitude of the voltage traces were distorted, key features such as shock impact could still be observed, and shock tracker gauges were still effective. The case of metallic barriers was also examined and similar effects observed. This study has indicated that while a coarse empirical correction is possible, uncertainty in the validity of the correction would preclude the use of dynamic metallic elements in experiments where high fidelity data is required.

The cylindrical isentropic compression by ultrahigh magnetic field (MC-1) is a kind of unique high energy density technique. It has characters like ultrahigh pressure and low temperature rising, and would have widely used in areas like high pressure physics, new material synthesis and ultrahigh magnetic field physics. The Institute of Fluid Physics, Chinese Academy of Engineering Physics (IFP, CAEP) has begun the experiment since 2011 and a primary experimental device had been set-up. In the experiments, a seed magnetic field of 5 Tesla were set-up first and compressed by a stainless steel liner which is driven by high explosive initiated synchronously. The internal diameter of the liner is 97 mm, and its thickness is 1.5 mm. The movement of liner was recorded optically and a typical turnaround phenomenon was observed. From the photography results the liner was compressed smoothly and evenly and its average velocity was about 5-6 km/s. In the experiment a axial magnetic field of over 1400 Tesla has been recorded. The MC-1 process was numerical simulated by 1D MHD code MC11D and the simulations are in accord with the experiments.

The ability to soft-launch projectiles to velocities exceeding 10 km/s is of interest for a number of scientific fields, including orbital debris impact testing and equation of state research. Current soft-launch technologies have reached a performance plateau below this operating range. In the implosion-driven launcher (ILD) concept, explosives are used to dynamically compress a light driver gas to significantly higher pressures and temperatures than the propellant of conventional light-gas guns. The propellant of the IDL is compressed through the linear implosion of a pressurized tube. The imploding tube behaves like a piston which travels into the light gas at the explosive detonation velocity, thus forming an increasingly long column of shock-compressed gas which can be used to propel a projectile. The McGill designed IDL has demonstrated the ability to launch a 0.1-g projectile to 9.1 km/s. This work will focus on the implementation of a novel launch cycle in which the explosively driven piston is accelerated in order to gradually increase driver gas compression, thus maintaining a relatively constant projectile driving pressure. The theoretical potential of the concept as well as the experimental development of an accelerating piston driver will be examined.

There are few reliable methods for obtaining equations of state for fluids under static pressure. We are developing confocal microscopy to investigate fluids in a diamond-anvil cell. Unlike conventional optical microscopy, confocal microscopes collect data point-by-point, enabling three-dimensional image reconstruction. By combining these images with Fabry-Perot interference measurements, we determine the volume and refractive index, as a function of pressure, in the same experiment.

Coherent anti-Stokes Raman spectroscopy (CARS) is reported following shock loading for the liquids phenylacetylene (18 and 13 GPa), cyclohexane (17 GPa), and acrylonitrile (17 GPa). The evolution of the spectra over the first 300 ps was recorded in each case. All spectra show monotonic decay of all peaks with increasing time after shock. No new peaks due to either chemical reaction or pressure shifting of the vibrational frequencies were observable. This loss of signal after shock is attributed to the decreased coherence time in the shock heated liquids, which leads to rapid signal loss in the nonresonant background free version of CARS used in the measurements. These results suggest that more complex methods may be required to measure picosecond shock induced chemistry with coherent Raman techniques that are free of nonresonant background interference.

Photonic Doppler Velocimetry (PDV, also known as LDV or HetV) is a remarkable tool for measuring the different velocities of many objects simultaneously, including tiny individual reflectors such as particles ejected by the rear face of a metallic plate damaged by a shock. This paper presents simplified experiments in which calibrated particles are accelerated and observed with PDV. They were shock-loaded using a pulsed laser (0.7 J, 10 ns, 532 nm) resulting in an acceleration up to 100 m/s. Various experiments have been performed to study the influence of different particle parameters: the material (Cu, Al), the size (10 to 200 micrometers) and the shape (sphere or rods). We recorded the back-reflected light with both orthogonal and tilted probes, and present the corresponding PDV spectrograms displaying cloud velocities as well as velocity tracks due to single particles. All of them decelerate within the ambient gas, while some rods also rotate. By applying simple models of deceleration and rotation, we try to retrieve their sizes or to evaluate their initial velocities. In addition, the tilted probes could be used to infer information on the global shape of the moving particle clouds.

Photon Doppler velocimetry (PDV) has made the transition among many experimental groups from being a new diagnostic to being routinely fielded as a means of obtaining velocity data in high-speed test applications. Indeed, research groups both within and outside of the shock physics community have taken note of PDV's robust, high-performance measurement capabilities. As PDV serves as the primary diagnostic in an increasing number of experiments, it will continue to find new applications and enable the measurement of previously un-measurable phenomena. This paper provides a survey of recent developments in PDV system design and feature extraction as well as a discussion of new applications for PDV. More specifically, changes at the system level have enabled the collection of data sets that are far richer than those previously attainable in terms of spatial and temporal coverage as well as improvements over PDV's previously measurable velocity ranges. And until recently, PDV data have been analyzed almost exclusively in the frequency-domain; although the use of additional data analysis techniques is beginning to show promise, particularly as it pertains to extracting information from a PDV signal about surface motion that is not along the beam's axis.

Preliminary experiments are performed to assess the utility of using the shock wave image framing technique (SWIFT) to characterize high explosive (HE) performance on detonator length and time scales. Columns of XTX 8004, an extrudable RDX-based high explosive, are cured directly within polymethylmethacrylate (PMMA) dynamic witness plates, and SWIFT is employed to directly visualize shock waves driven into PMMA through detonation interaction. Current experiments investigate two-dimensional, axisymmetric test geometries that resemble historic aquarium tests, but on millimeter length scales, and the SWIFT system records 16-frame, time-resolved image sequences at 190 ns inter-framing. Detonation wave velocities are accurately calculated from the time-resolved images, and standard aquarium-test analysis is evaluated to investigate calculated shock pressures at the HE/PMMA interface. Experimental SWIFT results are discussed where the charge diameter of XTX 8004 is varied from 2.0 mm to 6.5 mm.

The shock tube is a versatile apparatus used in a wide range of scientific research fields. In this case, we are developing a system to use with biological specimens. The process of diaphragm rupture is closely linked to the shock wave generated. Experiments were performed on an air-driven shock tube with Mylar^® and aluminium diaphragms of various thicknesses, to control the output. The evolution of shock pressure was measured and the diaphragm rupture process investigated. Single-diaphragm and double-diaphragm configurations were employed, as were open or closed tube configurations. The arrangement was designed to enable high-speed photography and pressure measurements. Overall, results are highly reproducible, and show that the double-diaphragm system enables a more controllable diaphragm burst pressure. The diaphragm burst pressure was linearly related to its thickness within the range studied. The observed relationship between the diaphragm burst pressure and the generated shock pressure presents a noticeable difference compared to the theoretical ideal gas description. Furthermore, the duration of the primary shock decreased proportionally with the length of the high-pressure charging volume. Computational modelling of the diaphragm breakage process was carried out using the ANSYS software package.

The results of experimental testing of shock wave generators, based on irregular Mach reflection of shock waves in a conical geometry, along with the results of numerical simulation is presented. The shock in a layered cylindrical central body was produced by an impact of a converging conical flyer plate. Conical flyer plate was originating from initially cylindrical cavity liner in a cylindrical HE charge that was launched by a sliding detonation. This approach led to device simplification, since manufacturing of conical parts from metal and explosive is not required. The sequential detonation of HE charge by a multi- point distributor was employed to vary the geometry of formed conical flyer. The dependence of parameters of shock wave in cylindrical Polymethylmethacrylate (PMMA) core on launch angle was investigated. It was found that launch angles below 10° lead to failure of the Mach reflection mode, while larger angles produced flat Mach disks that can be utilized in various shock experiments.

We present results from PDV (Photonic Doppler Velocimetry, also known as HetV -Heterodyne Velocimetry) experiments in which particles are ejected from shock-loaded metallic plates. The shocks induced in the samples are generated using high-explosive plane-wave generators. We manage to accelerate calibrated particles placed in the spot facings of a metal transmitter. These micron-sized spherical particles are made of copper or gold. The slowing down of the particles in air is observed; using their dragging behavior, we can therefore roughly infer both initial velocity and diameter distributions.

The mechanical and chemical response of energetic materials is controlled by a convolution of deformation mechanisms that span length scales and evolve during impact. Traditional methods use continuum measurements to infer the microstructural response whereas advances in synchrotron capabilities and diagnostics are providing new, unique opportunities to interrogate materials in real time and in situ. Experiments have been performed on a new gas-gun system (IMPact system for Ultrafast Synchrotron Experiments) using single X-ray bunch phase contrast imaging (PCI) and Laue diffraction at the Advanced Photon Source (APS). The low absorption of molecular materials maximizes x-ray beam penetration, allowing measurements in transmission using the brilliance currently available at APS Sector 32. The transmission geometry makes it possible to observe both average lattice response and spatially heterogeneous, continuum response (1-4 um spatial resolution over ~2 × 2 mm area, 80 ps exposure, 153 ns frame-rate) in energetic materials ranging from single crystals to plastic-bonded composites. The current work describes our progress developing and using these diagnostics to observe deformation mechanisms relevant to explosives and the first experiments performed with explosives on IMPULSE at APS.

We measured the response of short FBGs to a weak planar shock wave. The combined effect of the Photo-Elastic effect and the FBG strain was estimated theoretically depending on its orientation with respect to shock front (for 1550 nm FBG, parallel: 0.9 nm/kbar, perpendicular: -1.4 nm/kbar). The experimental results imply that the FBG/fibre survives for more than 1 μs at 5 kbar shock stress, and that our assumptions about the FBG behaviour under dynamic loading are valid, though more work is needed to fully quantify the effect.

An all optical-fiber-based approach to measuring high explosive detonation front position and velocity is demonstrated. By measuring total light return using an incoherent light source reflected from a fiber Bragg grating sensor in contact with the explosive, dynamic mapping of the detonation front position and velocity versus time is obtained. We demonstrate two examples of detonation front measurements: PETN detasheet test and detonation along a multi-HE cylindrical rate stick containing sections of PBX 9501, Comp B, TNT, PBX 9407, PBX 9520, and inert PMMA. In the PETN detasheet measurement, excellent agreement with complementary diagnostics (electrical pins) is achieved, with accuracy in the detonation front velocity at the 0.13% level when compared to the results from the pin data.

We present recent efforts at Los Alamos National Laboratory (LANL) to develop sensors for simultaneous, in situ pressure and temperature measurements under dynamic conditions by using an all-optical fiber-based approach. While similar tests have been done previously in deflagration-to-detonation tests (DDT), where pressure and temperature were measured to 82 kbar and 400°C simultaneously, here we demonstrate the use of embedded fiber grating sensors to obtain high temporal resolution, in situ pressure measurements in inert materials. We present two experimental demonstrations of pressure measurements: (1) under precise shock loading from a gas-gun driven plate impact and (2) under high explosive driven shock in a water filled vessel. The system capitalizes on existing telecom components and fast transient digitizing recording technology. It operates as a relatively inexpensive embedded probe (single-mode 1550 nm fiber-based Bragg grating) that provides a continuous fast pressure record during shock and/or detonation. By applying well-controlled shock wave pressure profiles to these inert materials, we study the dynamic pressure response of embedded fiber Bragg gratings to extract pressure amplitude of the shock wave and compare our results with particle velocity wave profiles measured simultaneously.

We have designed a miniature ceramic anvil high pressure cell (mCAC) for magnetic measurements at pressures up to 12.6 GPa in a commercial superconducting quantum interference (SQUID) magnetometer [1-3]. The simplified mCAC without anvil alignment mechanism is easy-to-use for researchers who are not familiar with high-pressure technology and magnetic measurements can be done above 10 GPa. Here, we show one additional modification in the mCAC. This modification enables more precise magnetic measurements on samples with smaller magnetization. We confirm the spontaneous dc magnetization in the pressure-induced ferromagnetic phase in YbCu₂Si₂ by high pressure magnetic measurements with the mCAC. The pressure-induced phase has the strong uniaxial Ising-type anisotropy.

Microwave interferometry is a useful technique for understanding the development and propagation of detonation waves. The velocity of the front can be determined directly with the dielectric constant of the explosive and the instantaneous phase difference of the reflected microwave signal from the detonation front. However, the dielectric constant of HMX-based explosives has been measured only over a small range of wavelengths. Here we employ an open-ended coaxial probe to determine the complex dielectric constant for LX-10 and other HMX-based explosives over the 5-20 GHz range. The propagation of a detonation wave in a lightly-confined cylindrical charge geometry is described where the microwave-reflective properties of the detonation front are characterized with a waveguide. For comparison, piezoelectric pins were used to measure the detonation velocity and indirectly estimate the dielectric constant of LX-10 at 26.5 GHz. Future work in this area will also be discussed.

Ramp loading using graded-density-impactors as flyers in gas-gun-driven plate impact experiments can yield new and useful information about the equation of state and the strength properties of the loaded material. Selective Laser Melting, an additive manufacture technique, was used to manufacture a graded density flyer, termed the "bed of nails" (BON). A 2 mm thick × 100 mm diameter solid disc of stainless steel formed a base for an array of tapered spikes of length 6 mm and spaced 1 mm apart. The two experiments to test the concept were performed at impact velocities of 900 m/s and 1100 m/s using the 100 mm gas gun at the Institute of Shock Physics at Imperial College, London. In each experiment a BON flyer was impacted onto a copper buffer plate which helped to smooth out perturbations in the wave profile. The ramp delivered to the copper buffer was in turn transmitted to three tantalum targets of thicknesses 3, 5 and 7 mm, which were mounted in contact with the back face of the copper. Heterodyne velocimetry was used to measure the velocity-time history, at the back faces of the tantalum discs. The wave profiles display a smooth increase in velocity over a period of ~2.5 us, with no indication of a shock jump. The measured profiles have been analysed to generate a stress strain curve for tantalum. The results have been compared with the predictions of the Sandia National Laboratories hydrocode, CTH.