CADMIUM SIMULATION OF ORBITAL-DEBRIS SHIELD PERFORMANCE TO SCALED VELOCITIES OF 18-KM/S

An experimental technique is developed and used to simulate the response of aluminum debris shields for impacts up to 18 km/s. To simulate an aluminum impact on an aluminum shield, the velocity is reduced by a scale factor, and the impactor and bumper are surrogates that have the same dimensions as the originals, but are composed of a material whose specific energies of melting and vaporization are much lower than those of aluminum. Cadmium is used as the surrogate material, because it has unique properties that satisfy the attendant scaling requirements and because its velocity scale factor is 3.1, thereby allowing tests at actual velocities up to 5.8 km/s to simulate aluminum impacts at velocities up to 18 km/s. Such tests reproduce the initial momentum of an aluminum impactor and the impulse distribution delivered to the rear wall. Cadmium tests, at scaled velocities near 7 km/s, agreed well with aluminum tests near 7 km/s, both in terms of debris cloud geometry and the minimum impactor size for wall perforation. Simulations at higher scaled velocities showed that the minimum diameter for penetration increases with increasing velocities above 10.5 km/s, in sharp contrast to current empirical shield models.