Kevin L. Poormon

Penetration of 6061-T6511 aluminum targets by ogive-nose steel projectiles with striking velocities between 0.5 and 3.0 km/s

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 of aluminum plates with ogive-nose steel rods at normal and oblique impacts

Abstract 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.

SCALE MODEL EXPERIMENTS WITH CERAMIC LAMINATE TARGETS

Abstract 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.

Analysis of the UDRI tests on Nextel multi-shock shields

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 5020mm, 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.

Comparisons of cadmium and aluminum debris clouds

Abstract 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.

Advanced all-metal orbital debris shield performance at 7 to 17 km/s

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.