Hugoniot measurement by hyper-velocity impact at velocities up to 9 km/s using a two-stage light-gas gun under optimized shot conditions

The optimization for acceleration of a projectile was performed by varying piston mass in consideration with the correlation with projectile mass and the engineering limits of the two-stage light-gas gun, and the projectile velocity has been achieved 9.2 km/s using the optimum acceleration conditions. Moreover, the Hugoniot measurements of oxygen-free copper were performed using the line reflection method at pressures up to 380 GPa by symmetric impact. The tilt and curvature of shock front were investigated according to the impact velocity, and it is proved to be important that the continuous spatial profile of shock front would be recorded.     

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

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-gas 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.     

Hypervelocity impact tests and simulations of single whipple bumper shield concepts at 10km/s

A series of experiments has been performed to evaluate the effectiveness of a Whipple bumper shield to orbital space debris at impact velocities of 10 km/s. Upon impact by a 19 mm (0.87 mm thick, L/D 0.5) flier plate, the thin aluminum bumper shield disintegrates into a debris cloud. The debris cloud front propagates axially at velocities of 14 km/s and expands radially at a velocity of 7 km/s. Subsequent loading by the debris on a 3.2 mm thick aluminum substructure placed 114 mm from the bumper penetrates the substructure completely. However, when the diameter of the flier plate is reduced to 12.7 mm, the substructure, although damaged is not perforated. Numerical simulations performed using the multi-dimensional hydrodynamics code CTH also predict complete perforation of the substructure by the subsequent debris cloud for the larger flier plate. The numerical simulation for a 12.7 mm flier plate, however, shows a strong dependence on assumed impact geometry, i. e., a spherical projectile impact geometry does not result in perforation of the substructure by the debris cloud, while the flat plate impact geometry results in perforation.     

Hypervelocity penetration of gold rods into SiC-N for impact velocities from 2.0 to 6.2 km/s

This paper presents the experimental design and results of an advanced set of reverse ballistic experiments with long gold rods, impacting SiC-N ceramics at impact velocities from 2.0 to 6.2 km/s. Important issues for these experiments were the high accuracy and position requirements necessary to detect a possible failure wave or failure kinetics in SiC-ceramics as might be evidenced by a change in the slope of the penetration velocity–impact velocity curve. New and sophisticated evaluation methods were developed for this purpose and produced very reliable results. Analyses of the experimental results show clearly that there is no change in the slope of the penetration velocity–impact velocity curve, contrary to that inferred from previous data and analysis.     

Hypervelocity testing of advanced shielding concepts for spacecraft against impacts to 10 km/s

Experiments have been performed on NASA state-of-the-art hypervelocity impact shields using the Sandia Hypervelocity Launcher (HVL) to obtain test velocities greater than those achievable using conventional two stage light-gas sun technology. The objective of the tests was to provide the first experimental data on the advanced shielding concepts for evaluation of the analytical equations (shield performance predictors) at velocities previously unattainable in the laboratory, and for comparison to single Whipple Bumper Shileds (WBS) under similar loading conditions. The results indicate that significantly more mass is required on the back sheet of the WBS to stop an approximately flat-plate particle impacting at 7 km/sec and at 10 km/sec that the analytical equations (derived from spherical particle impact data) predicted. The Multi-Shock Shield (MSS) consists of four ceramic fabric bumpers, and is lighter in terms of areal density by up to 33%, but is as effective as the heavier WBS under similar impact conditions at about 10 km/s. The Mesh Double Bumper shield (MDB) consists of an aluminum wire mesh bumper, followed by a sheet of solid aluminum and a layer of Kevlar^® fabric. It provides a weight savings in terms of areal density of up to 35% compared to the WBS for impacts of around 10 km/s.     

Impact of thin aluminum sheets with aluminum spheres up to 9 km/s

The results of further development of the University of Dayton Research Institute (UDRI), three-stage, light-gas gun and impact test data are presented. We have successfully launched 2.38-mm-diameter aluminum spheres to velocities in excess of 9 km/s with no damage to the launcher components. The results of several tests in which 2.38-mm-diameter aluminum spheres impacted thin aluminum sheets at velocities up to 9.10 km/s are presented. Quantitative data obtained from these tests were used to extend previously established relationships to velocities which are typical of the collisions of orbital debris with spacecraft. These test results include: bumper-sheet hole diameter as a function of impact velocity; determination of the fragmentation-initiation-threshold velocity for spheres impacting very thin sheets; and continued demonstration of the “scalability” of the test results using the bumper-thickness-to-projectile-diameter ratio (t/D) as the scaling factor.     

Performance of Whipple shields at impact velocities above 9 km/s

The results of 18 impact tests performed on Whipple shields were compared to the predicted ballistic limits of the shields in the region where the impact velocity of the threatening particle was high enough to produce melting and incipient vaporization of the particle. Ballistic limit equations developed at NASA Johnson Space Center were used to determine nominal failure thresholds for two configurations of all-aluminum Whipple shields. In the tests, 2017-T4 aluminum spheres with diameters ranging from 1.40 to 6.35 mm were used to impact the shields at impact velocities ranging from 6.94 to 9.89 km/s. Two different aluminum alloys were used for the rear walls of a simple Whipple shield. The results of 13 tests using these simple Whipple shields showed they offered better-than-predicted capability as impact velocity increased and that the strength of the rear wall material appeared to have a smaller-than-predicted effect on the shield performance. The results of five tests using three configurations of a scaled Space Station shield - a plain shield at 0 degrees, two shields with multilayer insulation in the space between the bumper and the rear wall (also at 0 degrees), and two tests with the plain shield at 45 degrees obliquity - showed that these shields met their predicted capabilities.     

Reverse impact experiments against tungsten rods and results for aluminum penetration between 1.5 and 4.2 km/s

Reverse impact experiments against 0.76 mm diameter L/D = 20 tungsten rods have been conducted with a 38 mm diameter launch tube, two-stage light-gas gun using four 450 kV flash X-rays to measure penetration rates. Techniques for projectile construction, sample placement, alignment, and radiography are described. Data for penetration rate, consumption velocity, and total penetration were obtained for 28 mm diameter 6061-T651 aluminum cylinders at impact velocities between 1.5 and 4.2 km/s. It was found that penetration velocity was a linear function of impact velocity over this velocity range. Above 2 km/s impact velocity, penetration was completely hydrodynamic. There was substantial secondary penetration, and the total penetration increased linearly with impact velocity over the range 1.5 to 2.5 km/s.     

An impact technique to accelerate flier plates to velocities over 12 km/s

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 10⁹-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.     

Crater morphology at impact velocities between 8 and 17 km/s

The crater morphology of impacts in the velocity range between 8 and 17 km/s has been investigated Glass projectiles with diameters between 20 ωm and 200 ωm were impacted on targets of gold, tungsten, iron and aluminum. Data have been compiled for the dependence of the crater diameter D_c and the crater depth T_c on the projectile velocity.     

Hypervelocity impact of spaced plates by a mock kill vehicle

In support of the National Missile Defense (NMD) program, a series of Light Gas Gun (LGG) lethality tests were conducted at the Arnold Engineering Development Center (AEDC). A new projectile was designed for this test series that would be representative of aspects of a generic NMD system kill vehicle. A series of projectile development tests were performed during the design phase of the projectile. This paper reports the results from the second development shot, in which the projectile impacted normally against two thin aluminum target plates, spaced approximately 5.5 diameters apart. Results reported include the documentation of the damage to the first and second plates, the debris generated behind the first plate, and correlation of these with analytical and numerical predictions. Hydrocodes used for analyses included ALE3D, run by the Lawrence Livermore National Laboratory, and CTH, run by the Sandia National Laboratory. The purpose of the hydrocode analyses was to help in assessing the ability of these codes to predict the debris formation process and the target damage.     

Ultra-high velocity impacts: cratering studies of microscopic impacts from 3 km/s to 30 km/s

Cratering experiments performed under carefully controlled conditions at impact velocities ranging from 3 km/s to 30 km/s into a wide variety of target materials are presented. These impact experiments use the 6 MV vertical Van de Graaff accelerator of the Ion Beam Facility at the Los Alamos National Laboratory to electrostatically accelerate highly charged iron micro-spheres. The sub-micron spheres, from a random size distribution, are shocklessly accelerated along an 8 m flight path. Ultra-sensitive charge detectors monitor the passage of the projectiles at a rate of up to 100 projectiles/second. An online computer records and displays in real time the charge, velocity and mass of the projectiles and provides cross correlation between the events observed by the several in-flight charge detectors and impact detectors. Real-time logic controls an electrostatic kicker which deflects projectiles of selected charge and velocity onto the target. Thus each experiment consists of an ensemble of 10 to 40 impacts onto a single target within a narrow window of the projectile parameter space, providing excellent statistical resolution of each data point.

The target materials used include single crystal copper and single crystal aluminum, gold, and quartz as well as pyrolytic graphic and anoxy used in composite materials of interest to space applications. We also conducted impact experiments onto thin Mylar and nickel foils. This paper presents these experiments and summarizes the cratering characterization performed to date. Emphasis is placed on cratering results in several materials over a range of impact velocities.     

Measured charge generation by small mass impact at velocities between 1 and 45 km/s

The electrical charge that is generated by the impact of a small mass at velocities between 1 and 45 km/s was investigated using the Electrostatic Dust Accelerator of the Max-Planck-Institut in Heidelberg (MPI) and the Plasma Accelerator of the Lehrstuhl fu¨r Raumfahrttechnik (LRT) of the Technische Universita¨t Mu¨nchen (TUM). Glass beads were accelerated, and the targets were of different materials i.e., (Au, W, Fe, Al). The mass/velocity range of the accelerated small masses was: MPI: 10⁻¹⁵g−10g/ 1km/s−10g−5g/ 2km/s±_total of both polarities can be described by the empirical formula: Q^±_total =Cmv^β[Coulomb], C being a function of the density ratio of target/projectile, is approximately unity and β between 2.92 and 3.77. The charge detector is described and the results that were obtained in test series at both facilities are discussed in relation to the empirical formula.     

Particle launch to 19 km/s for micro-meteoroid simulation using enhanced three-stage light gas gun hypervelocity launcher techniques

Particle launch experiments were performed to study application of the enhanced hypervelocity launcher (EHVL), i.e. the third-stage addition to the two-stage gun, for launching micron to millimeter sized particulates at velocities unobtainable with a standard two-stage light gas gun launch. Three types of particles or fliers were tested along with several barrel designs. For micron scale particles fine-grain polycrystalline ceramics were impacted and fractured, launching particulate clouds at velocities of 15 km/s. Multiple titanium particles 400 μm diameter embedded in plastic were “shotgun” launched to velocities of 10 km/s. Flier plates of 3 mm diameter by 1 mm thick Ti6Al4V were launched to 19 km/s. All experiments used a second-stage projectile with graded density facing impacting a flier in an impact generated acceleration reservoir. This paper describes the modification and adaptation of the Sandia EHVL to provide micrometeoroid simulation capabilities.     

Whipple shield ballistic limit at impact velocities higher than 7 km/s

The Whipple bumper shield was the first system developed to protect space structures against Meteoroids and Orbital Debris (M/OD), and it is still extensively adopted. In particular, Whipple shields are used to protect several elements of the International Space Station, although the most exposed areas to the M/OD environment are shielded by innovative low weigh and high resistance systems.

Hydrocode simulations were used to predict the ballistic limit of a typical aluminium Whipple shield configuration for space applications in the impact velocity range not accessible by the available experimental techniques. The simulations were carried out using the AUTODYN-2D and the PAMSHOCK-3D codes, allowing to couple the gridless Smoothed Particles Hydrodynamics with the Lagrange grid-based techniques. The global damage of the structure after the impact was determined with particular attention to the back wall penetration, and the results obtained with the two hydrocodes were compared with those given by semi-empirical damage equations.

A few hypervelocity Light Gas Gun impact experiments, performed on the same shield configuration at velocities up to 7.2 km/s, were previously simulated in order to assess the capability and limitations of the two hydrocodes in reproducing the experimental results available in the lower velocity regime. The influence of material models on the numerical predictions is discussed.     

Ultra-high-speed deformation by impact of a projectile flying at speeds on the order of km s

An apparatus was developed to facilitate application of an electro-thermo-chemical accelerator to high-speed deformation experiments. The apparatus is designed on the principle of sequential collision of elastic bodies. Speeds ranging from 600 to 780 m s⁻¹ were achieved, and estimated strain rate of deformation is 10⁷ s⁻¹. The newly developed apparatus can be applied to various types of accelerators for attaining deformation speeds as high as several km s⁻¹. Transmission electron microscopy of aluminum deformed at high speed by use of the apparatus revealed the formation of very small stacking fault tetrahedra (SFTs). This observation is quite new for aluminum; previously, SFTs had not been observed in aluminum, although deformation had been carried out at strain rates lower than 10⁶ s⁻¹. Use of the apparatus promises to provide new insight into high-speed deformation.     

Hypervelocity impact of rod projectiles with L/D from 1 to 32

Beside a short remark on the “hydrodynamic theory of rod projectiles”, the paper deals with the terminal ballistic behaviour of cylindrical projectiles against semi-infinite targets. Experimental data of EMI, completed by results of some other authors, are presented. Crater parameters like depth, diameter and volume and their dependence on projectile velocity (up to 5000 m/s), projectile and target material properties, as well as L/D-ratios (1–32), will be discussed. Mainly the projectile materials steel and tungsten sinter-alloys are considered. Target materials are mild steel and high strength steel, an Al-alloy and a tungsten sinter-alloy. The results show that the influence of material density on the crater dimensions is considerably greater than the influence of strength. The L/D ratio determines the velocity dependence of crater depth, diameter and volume. At high velocities in the hydrodynamic regime, the crater depth of short cylinders (L/D 1) is approximately proportional to v_p^2/3 (V_p=projectile velocity). With increasing L/D-ratio, the slope of the penetration curves decreases and converges for rods (L/D 1) versus a saturation, i. e. becomes nearly independent on v_p. A consequence of this saturation is the existence of a so-called “tangent velocity”, above which an optimal increase of efficiency is only realized by increasing the projectile mass and not the velocity. Furthermore, ballistic limits of real targets like single plates and symmetric double plates meteorite bumper shield) are taken into account. The expected better performance of “segmented rods” is also discussed.