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%.
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.
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.
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.
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.
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%.
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.
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.
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.
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.
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.
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.
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].
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.
Understanding high pressure behavior of homogeneous as well as heterogeneous 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. At very high impact velocities, material properties will be subjugated to phase-changes, such as melting and vaporization. These phase states cannot be obtained through conventional gun technology. These processes need to be represented accurately in hydrodynamic codes to allow credible computational analysis of impact events resulting from hypervelocity impact. 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 km/s. 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.
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.
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.
Controlled impact methodology has been used on a powdergun to obtain dynamic behavior properties of Tributyl Phosphate (TBP). A novel test methodology is used to provide extremely accurate equation of state data of the liquid. A thin aluminum plate used for confining the liquid also serves as a diagnostic to provide reshock states and subsequent release adiabats from the reshocked state. Polar polymer, polyvinylidene fluoride (PVDF) gauges and velocity interferometer system for any reflector (VISAR) provided redundant and precise data of temporal resolution to five nanoseconds and shock velocity measurements of better than 1%. The design and test methodologies are presented in this paper.
Shock-induced depoling of the ferroelectric ceramic PZT 95/5 is utilized in a number of pulsed power devices. Several experimental and theoretical efforts are in progress in order to improve numerical simulations of these devices. In this study we have examined the shock response of normally poled PZT 95/5 under uniaxial strain conditions. On each experiment the current produced in an external circuit and the transmitted waveform at a window interface were recorded. The peak electrical field generated within the PZT sample was varied through the choice of external circuit resistance. Shock pressures were varied from 0.6 to 4.6 GPa, and peak electrical fields were varied from 0.2 to 37 kV/cm. For a 2.4 GPa shock and the lowest peak field, a nearly constant current governed simply by the remanent polarization and the shock velocity was recorded. Both decreasing the shock pressure and increasing the electrical field resulted in reduced current generation, indicating a retardation of the depoling kinetics.
Relatively straightforward changes in the optical design of a conventional optically recording velocity interferometer system (ORVIS) can be used to produce a line-imaging velocity interferometer wherein both temporal and spatial resolution can be adjusted over a wide range. As a result line-imaging ORVIS can be tailored to a variety of specific applications involving dynamic deformation of heterogeneous materials as required by the characteristic length scale of these materials (ranging from a few {micro}m for ferroelectric ceramics to a few mm for concrete). A line-imaging ORVIS has been successfully interfaced to the target chamber of a compressed gas gun driver and fielded on numerous tests in combination with simultaneous measurements using a dual delay-leg, ''push-pull'' VISAR system. These tests include shock loading of glass-reinforced polyester composites, foam reverberation experiments (measurements at the free surface of a thin aluminum plate impacted by foam), and measurements of dispersive velocity in a shock-loaded explosive simulant (sugar). Comparison of detailed spatially-resolved material response to the spatially averaged VISAR measurements will be discussed.
A new test methodology is described which allows access to loading rates that lie between split Hopkinson bar and shock-loading techniques. Gas gun experiments combined with velocity interferometry techniques have been used to experimentally determine the intermediate strain-rate loading behavior of Coors AD995 alumina and Cercom silicon-carbide rods. Graded-density materials have been used as impactors; thereby eliminating the tension states generated by the radial stress components during the loading phase. Results of these experiments demonstrate that the time-dependent stress pulse generated during impact allows an efficient transition from the initial uniaxial strain loading to a uniaxial stress state as the stress pulse propagates through the rod. This allows access to intermediate loading rates over 5 x 10{sup 3}/s to a few times 10{sup 4}/s.
Record-high impact speeds achieved using the Sandia Hyper Velocity Launcher have permitted a systematic study of shock-induced full vaporization of zinc. Pressures up to 5.5 Mbar and temperatures as high as 39000 K (∼3.4 eV) are induced in a thin zinc plate by impacting it with a tantalum flier at speeds up to 10.1 km/s. Such high pressures produce essentially full vaporization of the zinc because the thermodynamic release isentropes pass into the vapor dome near the critical point. To characterize vapor flow, the velocity history produced by stagnation of the zinc expansion products against a witness plate is measured with velocity interferometry. For each experiment, the time-resolved experimental interferometer record is compared with wave-code calculations using an analytical equation of state, called ANEOS, that is known to have performed quite well at lower impact speeds (less than -7 km/s) where vaporization is negligible. Significant discrepancies between experiment and calculation are shown to exist under conditions of the more recent higher impact speeds in excess of 7 km/s where the release isentrope appears to pass near the critical point.
Shock equation of state and strength data have been obtained on the explosive PBXW-128 over the pressure range O-3 GPa using gun impact techniques and velocity interferometry diagnostics. Nonlinear shock-velocity-versus-particle velocity behavior is observed. Possible mechanisms are discussed and a Hug.oniot equation of slate model for the data is provided.
Gas guns and velocity interferometric techniques have been used to determine the loading behavior of AD995 alumina rods 19 mm in diameter by 75 mm and 150 mm long, respectively. Graded-density materials were used to impact both bare and sleeved alumina rods while the velocity interferometer was used to monitor the axial-velocity of the free end of the rods. Results of these experiments demonstrate that (1) a time-dependent stress pulse generated during impact allows an efficient transition from the initial uniaxial strain loading to a uniaxial stress state as the stress pulse propagates through the rod, and (2) the intermediate loading rates obtained in this configuration lie between split Hopkinson bar and shock-loading techniques.
Development of well-controlled hypervelocity launch capabilities is the first step to understand material behavior at extreme pressures and temperatures not available using conventional gun technology. In this paper, techniques used to extend both the launch capabilities of a two-stage light-gas gun to 10 km/s and their use to determine material properties at pressures and temperature states higher than those ever obtained in the laboratory are summarized. Time-resolved interferometric techniques have been used to determine shock loading and release characteristics of materials impacted by titanium and aluminum fliers launched by the only developed three-stage light-gas gun at 10 km/s. In particular, the Sandia three stage light gas gun, also referred to as the hypervelocity launcher, HVL, which is capable of launching 0.5 mm to 1.0 mm thick by 6 mm to 19 mm diameter plates to velocities approaching 16 km/s has been used to obtain the necessary impact velocities. The VISAR, interferometric particle-velocity techniques has been used to determine shock loading and release profiles in aluminum and titanium at impact velocities of 10 km/s.
Gas guns and velocity interferometric techniques have been used to determine the loading behavior of an AD995 alumina rod 19 mm in diameter by 75 mm and 150 mm long, respectively. Graded-density materials were used to impact both bare and sleeved alumina rods while the velocity interferometer was used to monitor the axial-velocity of the free end of the rods. Results of these experiments demonstrate that (1) a time-dependent stress pulse generated during impact allows an efficient transition from the initial uniaxial strain loading to a uniaxial stress state as the stress pulse propagates through the rod, and (2) the intermediate loading rates obtained in this configuration lie between split Hopkinson bar and shock-loading techniques.
Planar impact experiments and wave profile measurements provided single and double shock equation of state data to 30 GPa. Both compression wave wave profile structure and release wave data were used to infer time-dependent strength and equation of state properties for soda-lime glass.
New, previously unpublished shock wave data on soda-lime glass are presented. These data are examined in light of recent experimental evidence for failure wave behavior in brittle solids. An underlying physical basis for failure waves is explored in terms of inelastic deformation kinetics processes.
Understanding high-pressure material behavior is crucial to address the physical processes associated with a variety of hypervelocity impact events related to space sciences such as orbital-debris impact on a debris shield. At very high impact velocities material properties will be dominated by phase-changes, such as melting or vaporization, which cannot be achieved at lower impact velocities. Development of well-controlled and repeatable hypervelocity launch capabilities is the first step necessary to improve our understanding of material behavior at extreme pressures and temperatures not currently available using conventional two-stage light-gas gun techniques. In this paper, techniques used to extend the launch capabilities of a two-stage light gas gun to 16 km/s are described. It is anticipated that this technology will be useful in testing, evaluating, and design of various debris shields proposed for use with many different spacecrafts before deployment.
In this paper a brief description of dynamic techniques commonly available for determining material property studies is presented. For many impact applications, the material generally experiences a complex loading path. In most cases, the initial loading conditions can be represented by the shock commonly referred to as the Hugoniot state. Subsequent loading or release structure, i.e., off-Hugoniot states would however be dependent on the physical processes dominating the material behavior. The credibility of the material model is tested by the accuracy of predictions of off-Hugoniot states. Experimental techniques commonly used to determine off-Hugoniot states are discussed in this survey.
An experimental technique is described to launch an intact ``chunk,`` i.e. a 0.3 cm thick by 0.6 cm diameter cylindrical titanium alloy (Ti-6Al-4V) flyer, to 10.2 km/s. The ability to launch fragments having such an aspect ratio is important for hypervelocity impact phenomenology studies. The experimental techniques used to accomplish this launch were similar but not identical to techniques developed for the Sandia HyperVelocity Launcher (HVL). A confined barrel impact is crucial in preventing the two-dimensional effects from dominating the loading response of the projectile chunk. The length to diameter ratio of the metallic chunk that is launched to 10.2 km/s is 0.5 and is an order of magnitude larger than those accomplished using the conventional hypervelocity launcher. The multi-dimensional, finite-difference (finite-volume), hydrodynamic code CTH was used to evaluate and assess the acceleration characteristics i.e., the in-bore ballistics of the chunky projectile launch. A critical analysis of the CTH calculational results led to the final design and the experimental conditions that were used in this study. However, the predicted velocity of the projectile chunk based on CTH calculations was {approximately} 6% lower than the measured velocity of {approximately}10.2 km/S.
A series of experiments has been performed on the Sandia HyperVelocity Launcher (HVL) to evaluate the effectiveness of a Whipple bumper shield to orbital space debris at impact velocities in excess of 10 km/s. Upon impact by a 0.67 g (0.87 mm thick) flier plate, the thin aluminum bumper shield disintegrates into a debris cloud. The debris cloud front propagates axially at velocities of {approximately}14 km/s and expands radially at a velocity of {approximately}7 km/s. Subsequent loading on a 3.2 mm thick aluminum substructure by the debris penetrates the substructure completely. However, when the mass of the flier plate is reduced to 0.33 g, the substructure, although damaged, is not perforated over the duration of the experiment. Numerical simulations performed using the multi-dimensional hydrodynamics code CTH also predict complete penetration of the substructure by the subsequent debris cloud for a 0.87 g flier plate. The numerical simulations for a 0.33 g flier plate show a strong dependence on assumed impact geometry. For the assumption of a spherical projectile impact geometry, perforation of the substructure by the subsequent debris cloud is not predicted by CTH.
In this paper, measurements on the quasi-isentropic compression of tungsten to stress levels of 250 GPa are reported. Results of these experiments have been compared to those obtained under shock loading conditions to comparable stresses. These experiments have allowed the determination of temperature, pressure, and loading rate effects on the dynamic yield strength of tungsten up to 250 GPa. These results show that the dynamic yield strength of tungsten is dependent on the loading rate with the strength being higher for the relatively slower rates of loading along the quasi-isentropic. The pressure dependence of the yield strength of tungsten is determined nearly independent of temperature effects from quasi-isentropic loading experiments to 250 GPa, because the temperature rise in an quasi-loading experiment is much lower than those associated with shock loading experiments.
Very high driving pressures (tens or hundreds of GPa), are required to accelerate flier plats to hypervelocities. This loading pressure pulse on the fiber plates must be nearly shockless to prevent the plate from melting or vaporizing. This is accomplished by using graded-density impactors referred to as ``pillows.`` When this graded-density material is used to impact a flier-plate in a modified two-stage light gas gun, nearly shockless megabar pressures are introduced into the flier plate. The pressure pulses must also be tailored to prevent spallation of the flier-plate. This technique has been used to launch nominally 1-mm-thick aluminum, magnesium and titanium (gram-size) intact plates to 10.4 km/s, and 0.5-mm-thick aluminum and titanium (half-gram size) intact plates to 12.2 km/s. This is the highest mass-velocity capability attained with laboratory launchers to data, and should open up new regimes of impact physics and lethality studies related to space sciences for laboratory investigations. 14 refs.
Very high pressure and acceleration is necessary to launch flier plates to hypervelocities. In addition, the high pressure loading must be uniform, structured, and shockless, i.e., time-dependent to prevent the flier plate from either fracturing or melting. In this paper, a novel technique is described which allows the use of 100 GPa megabar loading pressures and 10{sup 9}-g acceleration to launch intact flier plates to velocities of 12.2 km/s. The technique has been used to launch nominally 1-mm thick aluminum, magnesium and titanium alloy plates to velocities over 10 km/s, and 0.5-mm thick aluminum and titanium alloy plates to velocities of 12.2 km/s.
A systematic study is described which addresses the technical issues associated with launching flier-plates intact to hypervelocitites. First, very high pressures are needed to launch the flier plates to hypervelocitites, and second this high pressure loading must be uniform and nearly shockless. To achieve both these criteria, a graded-density material referred to as a pillow'' is used to impact a flier plate. When this graded-density material is used to impact a flier plate at high velocities on a two-stage light-gas gun, nearly shockless megabar pressure pulses are introduced into the flier plate. Since the loading on the flier plate is shockless, melting of the flier plate is prevented. This technique has been used to launch a 2-mm thick titanium alloy (Ti-6Al-4V) plate to a velocity of 8.1 km/s, and a 1-mm thick aluminum alloy (6061-T6) plate to a velocity of 10.4 km/s. A method is described by which the flier plate velocities could be further augmented to velocities approaching 14 km/s. 18 refs., 16 figs.