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The dimensions of 96 holes produced by the impact of 2017-T4 aluminum spheres with various thicknesses of 6061-T6 aluminum sheets are presented and analyzed. The sphere diameters ranged from 1.40mm to 19.05mm and the sheet-thickness-to-projectile-diameter ratio, t/D, ranged from 0.008 to 0.618 with the majority of the tests having t/D ratios of less than 0.234. Impact velocities ranged from 1.98km/s to 9.89km/s. The measured hole diameters were normalized by dividing them by the diameter of the sphere that produced the hole. The normalized diameters of the holes are shown to scale when compared on the basis of t/D ratio. When the impact velocity was held constant, a relationship between the t/D ratio and the morphology of the lip structure surrounding the hole was noted. As the t/D ratio increased, the holes tended to be less circular and the lip morphology became more complex. The results of the analysis of all hole data was used to develop a description of the hole-formation sequence.

Titanium alloy, Ti-6Al-4 V, and commercially pure (CP) Titanium will be used to protect the Solar Probe Plus (SPP) spacecraft against hypervelocity impacts by solar dust particles. The results of six hypervelocity impact (HVI) tests performed on Ti-6Al-4 V and CP monolithic samples (3 each) are evaluated in terms of cratering and spall damage, and compared with crater depth and spall initiation predictions using the Ballistic Limit Equation (BLE) for Titanium shields developed at NASA Johnson Space Center and hydrocode computations. In the tests, 2017-T4 aluminum spheres with a diameter of 2.35 mm were used to impact the shields at an impact velocity of about 7 km/s. In general, the measured and predicted values of crater depth are found to be in good agreement with each other, regardless of the type of Titanium alloy. In terms of spall damage, two of the three Ti-6Al-4 V samples exhibit a noticeable incipient spall and one sample shows a very faint incipient spall, whereas only one of the CP samples shows a faint incipient spall. Polished cross- sections of the samples also indicate sub-crater damage modes such as microcracking, shear localization and large scale grain deformation, and possibly recrystallization. Differences observed in the macroscopic and microscopic damage phenomenologies exhibited by the two types of Titanium alloys are presented and discussed in terms of their implications on the BLE for shielding design calculations.

The results of 28 hypervelocity impact tests performed using a full-scale and two subscale versions of a simple Whipple shield and aluminum spheres are presented. “Pass/Fail” lines were developed for each subscale shield for impact velocities ranging from 6.90 to 9.77 km/s. These lines were compared to one another and to a scale-appropriate ballistic limit curve generated using Ballistic Limit Equations (BLE) from Christiansen. Both subscale shields exhibited similar performance capabilities when the impact velocity was near 7 km/s. The Christiansen BLE closely described the capability of a 0.46-scale shield but underpredicted the capability of a 0.25-scale shield, which improved when compared to the ballistic limit curve, as the impact velocity was increased. The performance of the full- scale shield was significantly below its predicted capability when the impact velocity was 7 km/s.

Whipple shields were first proposed as a means of protecting spacecraft from the impact of micrometeoroids in 1947 [1] and are currently in use as micrometeoroid and orbital debris shields on modern spacecraft. In the intervening years, the function of the thin bumper used to shatter or melt threatening particles has been augmented and enhanced by the use of various types and configurations of intermediate layers of various materials. All shield designs serve to minimize the threat of a spall failure or perforation of the main wall of the spacecraft as a result of the impact of the fragments. With increasing use of Whipple shields, various ballistic limit equations (BLEs) for guiding the design and estimating the performance of shield systems have been developed. Perhaps the best known and most used are the "new" modified Cour-Palais (Christiansen) equations [2]. These equations address the three phases of impact: (1) ballistic ( 7 km/s), where the projectile melts or vaporizes at impact. The performance of Whipple shields and the adequacy of the BLEs have been examined for the first two phases using the results of impact tests obtained from two-stage, light-gas gun test firings. Shield performance and the adequacy of the BLEs has not been evaluated in the melt/vaporization phase until now because of the limitations of launchers used to accelerate projectiles with controlled properties to velocities above 7.5 km/s. A three-stage, light-gas gun, developed at the University of Dayton Research Institute (UDRI) [3], is capable of launching small, aluminum spheres to velocities above 9 km/s. This launcher was used to evaluate the ballistic performance of two Whipple shield systems, various thermal protection system materials, and other spacecraft-related materials to the impact of 1.6-mm- to 2.6-mm-diameter, 2017-T4 aluminum spheres at impact velocities ranging from 8.91 km/s to 9.28 km/s. Test results, details of the shield systems, and nominal ballistic limits for the two Whipple shields are shown in Figures 1 and 2.

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.

An elusive goal of the hypervelocity impact community has been the evaluation of the ballistic response of space hardware to impact velocities ranging from 8 to 11 km/s using projectiles with known properties. The design, development, and use, during the 1960s, of a three-stage, light-gas gun at McGill University is reviewed. The developers of this gun claim that they were able to launch cylindrical, 12.7-mm-diameter Lexan disks with masses of 1.5 and 1.1 g to velocities of 9.6 and 10.5 km/s, respectively. This paper presents the results of an internally funded program at the University of Dayton Research Institute (UDRI) to duplicate the published performance of the McGill University launcher. A support structure and various components of a third stage which used an 8.1-mm-diameter launch tube were added to the UDRI 75/30-mm, two-stage, light-gas gun, making the arrangement of the components similar to the one used by McGill University. Work on the development of the UDRI three-stage, light-gas gun is a continuing effort, with the goal of successfully launching small diameter (∼3 mm or less) aluminum spheres to velocities in excess of 9 km/s. To date, the highest projectile velocity achieved with the UDRI three-stage, light-gas gun has been 8.65 km/s.

In this paper, we document the results of a combined experimental, analytical, and computational research program that investigates the penetration of steel projectiles into limestone targets at oblique angles. We first conducted a series of depth-of-penetration experiments using 20.0 g, 7.11-mm-diameter, 71.12-mm-long, vacuum-arc-remelted (VAR) 4340 ogive-nose steel projectiles. These projectiles were launched with striking velocities between 0.4 and 1.3 km/s using a 20-mm powder gun into 0.5 m square limestone target faces with angles of obliquity of 15° and 30°. Next, we employed the initial conditions obtained from the experiments with a technique that we have developed to calculate permanent projectile deformation without erosion. With this technique we use an explicit, transient dynamic, finite element code to model the projectile and an analytical forcing function based on the dynamic expansion of a spherical cavity to represent the target. Due to angle of obliquity we developed a new free surface effect model based on the solution of a dynamically expanding spherical cavity in a finite sphere of incompressible Mohr–Coulomb target material to account for the difference in target resistance acting on the top and bottom sides of the projectile. Results from the simulations show the final projectile positions are in good agreement with the positions obtained from post-test castings of the projectile trajectories.

In this paper we present the results from a combined experimental, analytical, and computational penetration program. First, we conducted a series of depth-of-penetration experiments using 0.021 kg, 7.11 mm diameter, 71.12 mm long, vacuum-arc-remelted 4340 ogive-nose steel projectiles. These projectiles were launched with striking velocities between 0.5 and 1.3 km/s using a 20 mm powder gun into 254 mm diameter, 6061-T6511 aluminum targets with angles of obliquity of 15°, 30°, and 45°. Next, we employed the initial conditions obtained from the experiments with a new technique that we have developed to calculate permanent projectile deformation without erosion. With this technique we use an explicit, transient dynamic, finite element code to model the projectile and an analytical forcing function derived from the dynamic expansion of a spherical cavity (which accounts for compressibility, strain hardening, strain-rate sensitivity, and a finite boundary) to represent the target. Results from the simulations show the final projectile positions are in good agreement with the positions obtained from post-test radiographs.

Summary We performed a series of depth-of-penetration experiments using 7.11-mm-diameter, 71.12-mm-long, ogive-nose steel projectiles and 254-mm-diameter, 6061-T6511 aluminum targets. The projectiles were made from vacuum-arc remelted (VAR) 4340 steel (Rc 38) and AerMet 100 steel (Rc 53), had a nominal mass of 0.021 kg, and were launched using a powder gun or a two-stage, light gas gun to striking velocities between 0.5 and 3.0 km/s. Since the tensile yield strength of AerMet 100 (Rc 53) steel is about 1.5 times greater than VAR 4340 (Rc 38) steel, we were able to demonstrate the effect of projectile strength on ballistic performance. Post-test radiographs of the targets showed three different regions of penetrator response as the striking velocity increased: (1) the projectiles remained rigid and visibly undeformed; (2) the projectiles deformed during penetration without nose erosion, deviated from the target centerline, and exited the side of the target or turned severely within the target; and (3) the projectiles eroded during penetration and lost mass. To show the effect of projectile strength, we present depth-of-penetration data as a function of striking velocity for both types of steel projectiles at striking velocities ranging from 0.5 and 3.0 km/s. In addition, we show good agreement between the rigid-projectile penetration data and a cavityexpansion model.

Perforation experiments were conducted with 26.3 mm thick, 6061-T651 aluminum plates and 12.9 mm diameter, 88.9 mm long, 4340 R c = 44 ogive-nose steel rods. For normal and oblique impacts with striking velocities between 280 and 860 m/s, we measured residual velocities and displayed the perforation process with X-ray photographs. These photographs clearly showed the time-resolved projectile kinematics and permanent deformations. In addition, we developed perforation equations that accurately predict the ballistic limit and residual velocities.

Ballistic impact experiments were performed on ceramic laminate targets at three scale sizes, nominally 1 3 , 1 6 , and 1 12 , to quantify the effects of scale on various responses, in particular, the ballistic limit velocity. The experiments were carefully designed and controlled so that the different scale sizes were high fidelity replicas of each other. A variety of responses, such as residual projectile quantities, hole size, and the extent of bulging, were measured. Some of the measured quantities showed little or no dependence on scale size, whereas other quantities, particularly the ballistic limit velocity, were found to vary with scale size. The percentage difference was quantified, and the results extrapolated to estimate full-scale response from the subscale tests.

Increasing demands on orbital debris shielding systems have spurred efforts to develop shields that are more efficient than the standard single-bumper system. For example, for a given total bumper mass, experiments at velocities near 7 km/s have shown that a multiple-bumper system is more efficient than a single bumper in preventing wall perforation. However, the performance of multiple bumper systems at velocities above 7 km/s is unknown. To address this problem, the cadmium surrogate-material technique described by Schmidt et al. [1] has been extended to two dual bumper systems. A complete dimensional analysis is developed to include similarity requirements for the intermediate layers. Results of experiments, for impact angles of 0° and 45°, are presented and compared to those for single bumpers, along with limited results for an equal-mass four-bumper shield. Surprisingly, for scaled velocities near 16 km/s at normal incidence, a single bumper defeats impactors approximately 30% larger in diameter than multiple bumpers of the same total areal density.

Results of a study comparing the debris clouds produced by hypervelocity impacts of cadmium spheres on cadmium bumper-sheets and aluminum spheres on aluminum bumper-sheets are presented. The shape, fragment size and distribution, and phase state of the cadmium and aluminum debris clouds were qualitatively compared and matched. The front, rear, and radial velocities of particles in the cadmium debris clouds were determined from radiographs and normalized by dividing by the impact velocity. These data were compared with similar aluminum debris velocity data to determine whether the debris velocities could be scaled by a constant value. Comparisons were made at the same bumper-thickness-to-projectile-diameter ratios ( t D ). The normalized debris velocities scaled reasonably well. The impact velocities for the aluminum tests were about two times greater than those of the cadmium tests to achieve the same normalized debris velocities. A velocity scaling technique is proposed in which the cadmium impact velocities are scaled using this factor and momentum is converted. Use of this scaling technique allows aluminum projectile impacts on aluminum bumper shields to be simulated to about 14 km/s using cadmium projectiles and cadmium bumper shields at velocities attainable with current launcher technology. A brief description is included on the phase transition from solid to liquid and liquid to vapor.

This paper analyzes the results of further development of the Nextel ceramic cloth, multiple-bumper or multi-shock shield, first presented at the 1989 HVIS and published as Cour-Palais and Crews (1990). The supporting hypervelocity impact testing was done by the University of Dayton Research Institute, Dayton, Ohio, in their Impact Physics Laboratory, using 0.953cm aluminum spheres and equal-mass (l/d=0.16) aluminum discs. The projectiles were launched at 6.6 to 6.9km/s by a 50 20 mm , two-stage light gas gun, normal to the targets. The objective of this development project was to investigate light-weight, flexible, multiple-bumper shields for possible use as protection for some elements of Space Station Freedom. The analysis discusses the performance of shields consisting of different combinations of Nextel ceramic cloth bumpers and aluminum rear sheets. Several Nextel fiber strengths and weaves were investigated as bumpers and a baseline, light-weight shield that met the failure criteria was established using the spherical aluminum projectiles. This same target was then tested against the aluminum discs to investigate the effect of projectile shape. The multi-shock phenomena was also investigated during this project using the UDRI multiple, orthogonal x-ray system to observe the first three or four sequential impacts of the projectile fragments. Some of these are reproduced in the paper, together with views of the associated rear sheet damage. Similarities between the shock effects of the Nextel and thin aluminum bumpers are shown, and the aluminum multiple-bumper shield results are used to further understand the multi-shock process. Finally, the paper modifies the equation constants given by Cour-Palais and Crews (1990), adds constants for the l/d=0.16 disc, and provides evidence that they scale with momentum to 10km/s.

Impact of foreign or domestic material on components in the hot section of gas turbines with ceramic components is a common cause of catastrophic failure. Several such occurrences were observed during engine testing under the Ceramic Stationary Gas Turbine program sponsored by the U.S. Department of Energy. A limited analysis was carried out at Solar Turbines Incorporated (Solar), which involved modeling of the impact in the hot section. Based on the results of this study an experimental investigation was carried out at the University of Dayton Research Institute Impact Physics Laboratory to establish the conditions leading to significant impact damage in silicon-based ceramics. The experimental set up involved impacting ceramic flexure bars with spherical metal particulates under conditions of elevated temperature and controlled velocity. The results of the study showed a better correlation of impact damage with momentum than with kinetic energy. Increased test specimen mass and fracture toughness were found to improve impact resistance. Continuous fiber-reinforced ceramic composite (CFCC) materials have better impact resistance than monolithics. A threshold velocity was established for impacting particles of a defined mass. Post-impact metallography was carried out at Oak Ridge National Laboratory to further establish the impact mechanism.