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Shock response of dry sand

Reinhart, William D.; Chhabildas, Lalit C.; Vogler, Tracy V.

The dynamic compaction of sand was investigated experimentally and computationally to stresses of 1.8 GPa. Experiments have been performed in the powder's partial compaction regime at impact velocities of approximately 0.25, 0.5, and 0.75 km/s. The experiments utilized multiple velocity interferometry probes on the rear surface of a stepped target for an accurate measurement of shock velocity, and an impedance matching technique was used to deduce the shock Hugoniot state. Wave profiles were further examined for estimates of reshock states. Experimental results were used to fit parameters to the P-Lambda model for porous materials. For simple 1-D simulations, the P-Lambda model seems to capture some of the physics behind the compaction process very well, typically predicting the Hugoniot state to within 3%.

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Advanced diagnostics for impact-flash spectroscopy on light-gas guns

Chhabildas, Lalit C.; Brown, Justin L.

This study is best characterized as new technology development for implementing new sensors to investigate the optical characteristics of a rapidly expanding debris cloud resulting from hypervelocity impact regimes of 7 to 11 km/s. Our gas guns constitute a unique test bed that match operational conditions relevant to hypervelocity impact encountered in space engagements. We have demonstrated the use of (1) terahertz sensors, (2) silicon diodes for visible regimes, (3) germanium and InGaAs sensors for the near infrared regimes, and (4) the Sandia lightning detectors which are similar to the silicon diodes described in 2. The combination and complementary use of all these techniques has the strong potential of ''thermally'' characterizing the time dependent behavior of the radiating debris cloud. Complementary spectroscopic measurements provide temperature estimates of the impact generated debris by fitting its spectrum to a blackbody radiation function. This debris is time-dependent as its transport/expansion behavior is changing with time. The rapid expansion behavior of the debris cools the cloud rapidly, changing its thermal/temperature characteristics with time. A variety of sensors that span over a wide spectrum, varying from visible regime to THz frequencies, now gives us the potential to cover the impact over a broader temporal regime starting from high pressures (Mbar) high-temperatures (eV) to low pressures (mbar) low temperatures (less than room temperature) as the debris expands and cools.

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Hypervelocity impact flash at 6, 11, and 25 KM/S

AIP Conference Proceedings

Lawrence, R.J.; Reinhart, William D.; Chhabildas, Lalit C.; Thornhill, T.F.

Impact-flash phenomenology has been known for decades, and is now being considered for missile-defense applications, in particular for remote engagement diagnostics. To technically establish this capability, we have conducted a series of experiments at impact velocities of ∼6, ∼11, and ∼25 km/s. Two- and three-stage light-gas guns were used for the lower two velocities, and magnetically-driven flyers on the Sandia Z machine achieved the higher velocity. Spectrally- and temporally-resolved flash output addressed data reproducibility, material identification, and target configuration analysis. Usable data were obtained at visible and infrared wavelengths. Standard atomic spectral databases were used to identify strong lines from all principal materials used in the study. The data were unique to the individual materials over the wide range of velocities and conditions examined. The time-varying nature of the signals offered the potential for correlation of the measurements with various aspects of the target configuration. Integrating the records over wavelength helped to clarify those time variations. © 2006 American Institute of Physics.

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Response to unloading and reloading of shock compressed polymethyl methacrylate

AIP Conference Proceedings

Reinhart, William D.; Chhabildas, Lalit C.

Shock properties of polymeric materials have been investigated at low stresses for use as windows for velocity interferometry, binder phases for polymer-bonded explosives, and as adhesives. The shock Hugoniot for many other polymeric materials may also exist. There are distinct advantages in using a low-impedance polymer for impactors on shock experiments, however the loading structure from reshock or release has not been determined at these high stresses. In this study polymethyl-methacrylate (PMMA) is shocked to approximately 45 GPa and recompressed up to 130 GPa as well as unloaded from the shocked state. Reloading and unloading wave speeds have been determined from this initial stress level of approximately 45 GPa. The results from these tests not only characterize PMMA at these stress states, but will be valuable when PMMA is used as a standard material to study strength and phase transformation behavior in other materials. © 2006 American Institute of Physics.

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Survey of the hypervelocity impact technology and applications

Chhabildas, Lalit C.

HVIS 2005 was a clear success. The Symposium brought together nearly two hundred active researchers and students from thirteen countries around the world. The 84 papers presented at HVIS 2005 constitute an ''update'' on current research and the state-of-the-art of hypervelocity science. Combined with the over 7000 pages of technical papers from the eight previous Symposia, beginning in 1986, all published in the International Journal of Impact Engineering, the papers from HVIS 2005 add to the growing body of knowledge and the progressing state-of-the-art of hypervelocity science. It is encouraging to report that even with the limited funding resources compared to two decades ago, creativity and ingenuity in hypervelocity science are alive and well. There is considerable overlap in different disciplines that allows researchers to leverage. Experimentally, higher velocities are now available in the laboratory and are ideally suited for space applications that can be tied to both civilian (NASA) and DoD military applications. Computationally, there is considerable advancement both in computer and modeling technologies. Higher computing speeds and techniques such as parallel processing allow system level type applications to be addressed directly today, much in contrast to the situation only a few years ago. Needless to say, both experimentally and computationally, the ultimate utility will depend on the curiosity and the probing questions that will be incumbent upon the individual researcher. It is quite satisfying that over two dozen students attended the symposium. Hopefully this is indicative of a good pool of future researchers that will be needed both in the government and civilian industries. It is also gratifying to note that novel thrust areas exploring different and new material phenomenology relevant to hypervelocity impact, but a number of other applications as well, are being pursued. In conclusion, considerable progress is still being made that is beneficial for continuous development of hypervelocity impact technology and applications even with the relatively limited resources that are being directed in this field.

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Dynamic response of shock-loaded multi-component glasses

Alexander, Charles S.; Vogler, Tracy V.; Reinhart, William D.; Chhabildas, Lalit C.

Glass, in various formulations, may be useful as a transparent armor material. Fused quartz (SiO{sub 2}), modified with either B{sub 2}O{sub 3} (13 % wt.) or Na{sub 2}O (15 % wt.), was studied to determine the effect on the dynamic response of the material. Utilizing powder and two-stage light gas guns, plate impact experiments were conducted to determine the effect on strength properties, including the elastic limits and plastic deformation response. Further, the effect of glass modification on known transitions to higher density phases in fused quartz was evaluated. Results of these experiments will be presented and discussed.

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Hugoniot and strength behavior of silicon carbide

Proposed for publication in the Journal of Applied Physics.

Vogler, Tracy V.; Reinhart, William D.; Chhabildas, Lalit C.

The shock behavior of two varieties of the ceramic silicon carbide was investigated through a series of time-resolved plate impact experiments reaching stresses of over 140 GPa. The Hugoniot data obtained are consistent for the two varieties tested as well as with most data from the literature. Through the use of reshock and release configurations, reloading and unloading responses for the material were found. Analysis of these responses provides a measure of the ceramic's strength behavior as quantified by the shear stress and the strength in the Hugoniot state. While previous strength measurements were limited to stresses of 20-25 GPa, measurements were made to 105 GPa in the current study. The initial unloading response is found to be elastic to stresses as high as 105 GPa, the level at which a solid-to-solid phase transformation is observed. While the unloading response lies significantly below the Hugoniot, the reloading response essentially follows it. This differs significantly from previous results for B{sub 4}C and Al{sub 2}O{sub 3}. The strength of the material increases by about 50% at stresses of 50-75 GPa before falling off somewhat as the phase transformation is approached. Thus, the strength behavior of SiC in planar impact experiments could be characterized as metal-like in character. The previously reported phase transformation at {approx}105 GPa was readily detected by the reshock technique, but it initially eluded detection with traditional shock experiments. This illustrates the utility of the reshock technique for identifying phase transformations. The transformation in SiC was found to occur at about 104 GPa with an associated volume change of about 9%.

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Variability in dynamic properties of tantalum : spall, attenuation and load/unload

Reinhart, William D.; Trott, Wayne T.; Chhabildas, Lalit C.; Vogler, Tracy V.

A suite of impact experiments was conducted to assess spatial and shot-to-shot variability in dynamic properties of tantalum. Samples had a uniform refined {approx}20 micron grain structure with a strong axisymmetric [111] crystallographic texture. Two experiments performed with sapphire windows (stresses of approximately 7 and 12 GPa) clearly showed elastic-plastic loading and slightly hysteretic unloading behavior. An HEL amplitude of 2.8 GPa (corresponding to Y 1.5 GPa) was observed. Free-surface spall experiments showed clear wave attenuation and spallation phenomena. Here, loading stresses were {approx} 12.5 GPa and various ratios of impactor to target thicknesses were used. Spatial and shot-to-shot variability of the spall strength was {+-} 20%, and of the HEL, {+-} 10%. Experiments conducted with smaller diameter flyer plates clearly showed edge effects in the line and point VISAR records, indicating lateral release speeds of roughly 5 km/s.

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Multi-dimensional hydrocode analyses of penetrating hypervelocity impacts

Lawrence, R.J.; Bessette, Gregory B.; Lawrence, R.J.; Chhabildas, Lalit C.; Reinhart, William D.; Thornhill, Tom F.; Saul, WVenner S.

The Eulerian hydrocode, CTH, has been used to study the interaction of hypervelocity flyer plates with thin targets at velocities from 6 to 11 km/s. These penetrating impacts produce debris clouds that are subsequently allowed to stagnate against downstream witness plates. Velocity histories from this latter plate are used to infer the evolution and propagation of the debris cloud. This analysis, which is a companion to a parallel experimental effort, examined both numerical and physics-based issues. We conclude that numerical resolution and convergence are important in ways we had not anticipated. The calculated release from the extreme states generated by the initial impact shows discrepancies with related experimental observations, and indicates that even for well-known materials (e.g., aluminum), high-temperature failure criteria are not well understood, and that non-equilibrium or rate-dependent equations of state may be influencing the results.

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Dynamic behavior of boron carbide

Proposed for publication in Journal of Applied Physics.

Vogler, Tracy V.; Vogler, Tracy V.; Reinhart, William D.; Chhabildas, Lalit C.

Boron carbide displays a rich response to dynamic compression that is not well understood. To address poorly understood aspects of behavior, including dynamic strength and the possibility of phase transformations, a series of plate impact experiments was performed that also included reshock and release configurations. Hugoniot data were obtained from the elastic limit (15-18 GPa) to 70 GPa and were found to agree reasonably well with the somewhat limited data in the literature. Using the Hugoniot data, as well as the reshock and release data, the possibility of the existence of one or more phase transitions was examined. There is tantalizing evidence, but at this time no phase transition can be conclusively demonstrated. However, the experimental data are consistent with a phase transition at a shock stress of about 40 GPa, though the volume change associated with it would have to be small. The reshock and release experiments also provide estimates of the shear stress and strength in the shocked state as well as a dynamic mean stress curve for the material. The material supports only a small shear stress in the shocked (Hugoniot) state, but it can support a much larger shear stress when loaded or unloaded from the shocked state. This strength in the shocked state is initially lower than the strength at the elastic limit but increases with pressure to about the same level. Also, the dynamic mean-stress curve estimated from reshock and release differs significantly from the hydrostate constructed from low-pressure data. Finally, a spatially resolved interferometer was used to directly measure spatial variations in particle velocity during the shock event. These spatially resolved measurements are consistent with previous work and suggest a nonuniform failure mode occurring in the material.

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Tube fragmentation of multiple materials

Vogler, Tracy V.; Thornhill, Tom F.; Chhabildas, Lalit C.; Vogler, Tracy V.

In the current study we are developing an experimental fracture material property test method specific to dynamic fragmentation. This test method allows the study of fracture fragmentation in a reproducible laboratory environment under well-controlled loading conditions. Motion and fragmentation of the specimen are diagnosed using framing camera, VISAR and soft recovery methods. Fragmentation properties of several steels, nitinol, tungsten alloy, copper, aluminum, and titanium have been obtained to date. The values for fragmentation toughness, and failure threshold will be reported, as well as effects in these values as the material strain-rate is varied through changes in wall thickness and impact conditions.

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Hyperveolcity impacts on aluminum from 6 to 11 km/s for hydrocode benchmarking

Chhabildas, Lalit C.; Chhabildas, Lalit C.; Reinhart, William D.; Thornhill, Tom F.; Bessette, Gregory B.; Saul, WVenner S.; Lawrence, R.J.; Kipp, Marlin E.

A systematic computational and experimental study is presented on impact generated debris resulting from record-high impact speeds recently achieved on the Sandia three-stage light-gas gun. In these experiments, a target plate of aluminum is impacted by a titanium-alloy flyer plate at speeds ranging from 6.5 to 11 km/s, producing pressures from 1 Mb to over 2.3 Mb, and temperatures as high as 15000 K (>1 eV). The aluminum plate is totally melted at stresses above 1.6 Mb. Upon release, the thermodynamic release isentropes will interact with the vapor dome. The amount of vapor generated in the debris cloud will depend on many factors such as the thickness of the aluminum plate, super-cooling, vaporization kinetics, the distance, and therefore time, over which the impact-generated debris is allowed to expand. To characterize the debris cloud, the velocity history produced by stagnation of the aluminum expansion products against a witness plate is measured using velocity interferometry. X-ray measurements of the debris cloud are also recorded prior to stagnation against an aluminum witness plate. Both radiographs and witness-plate velocity measurements suggest that the vaporization process is both time-dependent and heterogeneous when the material is released from shocked states around 230 GPa. Experiments suggest that the threshold for vaporization kinetics in aluminum should become significant when expanded from shocked states over 230 GPa. Numerical simulations are conducted to compare the measured x-ray radiographs of the debris cloud and the time-resolved experimental interferometer record with calculational results using the 3-D hydrodynamic wavecode, CTH. Results of these experiments and calculations are discussed in this paper.

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HVL{_}CTH: A Simple Tool That Simulates The Hyper-Velocity Launch of a Flyer Plate

Vogler, Tracy V.; Vogler, Tracy V.; Chhabildas, Lalit C.

Sandia National Laboratories has developed a unique method for a hyper-velocity launch (HVL), the three-stage gun. The three-stage gun is a modified two-stage light-gas gun, consisting of a piston used in the first stage, an impactor in the second stage, and a flyer plate in the third stage. The impactor is made up of different material layers that are increasing in shock impedance. The graded or pillowed layers allow the flyer to be launched at velocities up to 16 km/s without the formation of a single shock wave in the flyer plate and without it melting. Under certain experimental conditions the flyer velocity cannot be measured by standard means, X-rays and VISAR. Also, there is a need to know the flyer velocity prior to a launch in order to calibrate instruments and determine the appropriate shot configuration. The objective of HVL{_}CTH is to produce an accurate forecast of the flyer plate velocity under different launch conditions. CTH is a Eulerian shock physics computational analysis package developed at Sandia National Laboratories. Using CTH requires knowledge of its syntax and capabilities. HVL{_}CTH allows the user to easily interface with CTH, through the use of Fortran programs and batch files, in order to simulate the three-stage launch of a flyer plate. The program, HVL{_}CTH, requires little to no knowledge of the CTH program and greatly reduces the time needed to calculate the flyer velocity. Users of HVL{_}CTH are assumed to have no experience with CTH. The results from HVL{_}CTH were compared to results of X-ray and VISAR measurements obtained from HVL experiments. The comparisons show that HVL{_}CTH was within 1-2% of the X-Ray and VISAR results most of the time.

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Dynamic properties of AerMet® 100 steels to 25 GPa

Journal De Physique. IV : JP

Chhabildas, Lalit C.; Reinhart, William D.

Well-controlled impact studies have been conducted on "as-received" and heat-treated AerMet® 100 steel alloy samples to determine their dynamic material properties. Gas guns and time-resolved laser interferometry have been used to measure the fine structure in the particle velocity profiles resulting from symmetric plate impact. Impact velocities ranged from 0.40 km/s to 1.20 km/s. These experiments have allowed us to estimate the dynamic yield strength, and the spall strength of the "as-received" and heat-treated AerMet® 100 steel. The as-received material undergoes a phase transformation at around 13 GPa, while the heat-treated material exhibits the phase change at ∼ 15GPa. The results of this study clearly suggest that the dynamic yield strength, spall strength and the phase transition kinetics are influenced by the heat-treatment.

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Multicomponent-Multiphase Equation of State for Carbon

Kerley, Gerald I.; Chhabildas, Lalit C.; Chhabildas, Lalit C.

The unique properties of carbon have made it both a fascinating and an important subject of experimental and theoretical studies for many years [1]-[4]. The contrast between its best-known elemental forms, graphite and diamond, is particularly striking. Graphite is black, has a rather low density and high compressibility (close to that of magnesium), and is greasy enough to be useful as a lubricant and in pencil leads. Diamond is brilliantly translucent, 60% more dense than graphite, less compressible than either tungsten or corundum, and its hardness makes it useful for polishing and cutting. This variability in properties, as well as that observed among the many classes of carbon compounds, arises because of profound differences in electronic structure of the carbon bonds [5]. A number of other solid forms of carbon are known. Pyrolytic graphite [6] is a polycrystalline material in which the individual crystallites have a structure quite similar to that of natural graphite. Fullerite (solid C 60), discovered only ten years ago [7], consists of giant molecules in which the atoms are arranged into pentagons and hexagons on the surface of a spherical cage. Amorphous carbon [8][9], including carbon black and ordinary soot, is a disordered form of graphite in which the hexagonally bonded layers are randomly oriented. Glassy carbons [9][10], on the other hand, have more random structures. Many other structures have been discussed [1][9].

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Equation of state measurements of materials using a three-stage gun to impact velocities of 11 KM/S

International Journal of Impact Engineering

Reinhart, William D.; Chhabildas, Lalit C.; Carroll, Daniel E.; Bergstresser, Thomas K.; Thornhill, Tom F.; Winfree, Nancy A.

Results of an experimental series performed utilizing a three-stage gun to obtain precise material property equation of state (EOS) data for a titanium alloy (Ti6-Al-4V) at extreme pressure states that are not currently attainable using conventional two-stage light-gas gun technology is reported herein. What is new is the technique being implemented for use at engagement velocities exceeding 11 km/s. Shock-velocity in the target is being determined using 100 μm diameter fiber-optic pins and measuring shock transit times over a known distance between two parallel planes. These fiber-optic pins also indicate that the flyer-plate bow and tilt is comparable to two-stage light-gag gun technology. The thermodynamic state of the flyer plate prior to impact has also been determined both experimentally and calculationally. In particular, the temperature, and hence the density of the flyer-plate is also well known prior to impact. Results of these studies indicate that accurate Hugoniot information can be obtained using the three-stage light gas gun. This new test-methodology has extended the EOS of Ti6-Al-4V titanium alloy to stresses up to approximately 250 GPa. © 2001 Elsevier Science Ltd. All rights reserved.

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Dispersive Velocity Measurements in Heterogeneous Materials

Trott, Wayne T.; Castaneda, Jaime N.; Baer, Melvin B.; Chhabildas, Lalit C.; Knudson, Marcus D.; Davis, Jean-Paul D.; Asay, James R.

In order to provide real-time data for validation of three dimensional numerical simulations of heterogeneous materials subjected to impact loading, an optically recording velocity interferometer system (ORVIS) has been adapted to a line-imaging instrument capable of generating precise mesoscopic scale measurements of spatially resolved velocity variations during dynamic deformation. Combining independently variable target magnification and interferometer fringe spacing, this instrument can probe a velocity field along line segments up to 15 mm in length. In high magnification operation, spatial resolution better than 10 {micro}m can be achieved. For events appropriate to short recording times, streak camera recording can provide temporal resolution better than 0.2 ns. A robust method for extracting spatially resolved velocity-time profiles from streak camera image data has been developed and incorporated into a computer program that utilizes a standard VISAR analysis platform. The use of line-imaging ORVIS to obtain measurements of the mesoscopic scale dynamic response of shocked samples has been demonstrated on several different classes of heterogeneous materials. Studies have focused on pressed, granular sugar as a simulant material for the widely used explosive HMX. For low-density (65% theoretical maximum density) pressings of sugar, material response has been investigated as a function of both impact velocity and changes in particle size distribution. The experimental results provide a consistent picture of the dispersive nature of the wave transmitted through these samples and reveal both transverse and longitudinal wave structures on mesoscopic scales. This observed behavior is consistent with the highly structured mesoscopic response predicted by 3-D simulations. Preliminary line-imaging ORVIS measurements on HMX as well as other heterogeneous materials such as foam and glass-reinforced polyester are also discussed.

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Techniques for Equation-of-State Measurements on a Three-Stage Light-Gas Gun

Reinhart, William D.; Chhabildas, Lalit C.

Understanding high pressure behavior materials is necessary in order to address the physical processes associated with hypervelocity impact events related to space science applications including orbital debris impact and impact lethality. Until recently the highest-pressure states in materials have been achieved from impact loading techniques from two-stage light gas guns with velocity limitations of approximately 81cm/s. In this paper, techniques that are being developed and implemented to obtain the needed shock loading parameters (Hugoniot states) for material characterization studies, namely shock velocity and particle velocity, will be described at impact velocities up to 11 kds. The determination of equation-of-state (EOS) and thermodynamic states of materials in the regimes of extreme high pressures is now attainable utilizing the three-stage launcher. What is new in this report is that these techniques are being implemented for use at engagement velocities never before attained utilizing two-stage light-gas gun technology. The design and test methodologies used to determine Hugoniot states are described in this paper.

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Gas Gun Impact Testing of PZT 95/5, Part 1: Unpoled State

Furnish, Michael D.; Setchell, Robert E.; Chhabildas, Lalit C.; Montgomery, Stephen M.

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.

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43 Results
43 Results