Comparisons of cadmium and aluminum debris clouds

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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.