EVOLUTION OF DEBRIS PLUMES AS INFERRED FROM WITNESS PLATES

Photographic overviews and first-order interpretations are presented o f witness-plate damage patterns that were produced by 3.2 mm diameter (D-p) soda-lime glass projectiles penetrating targets of aluminum(1110 -0) and aluminum(6061-T6), Inconel, lead, and teflon at 6 km/s, and of additional aluminum(1100-0) targets penetrated at 2, 4, 5 and 6.7 km/ s. These targets varied systematically in thickness (T) from infinite halfspace to thin films (i.e., 0.1 < D-p/T < 1000). The witness-plate spray patterns from these diverse target materials have remarkably sim ilar characteristics determined in strict response to the absolute tar get thickness; velocity-dependent effects are minor by comparison. Mat erials emanating from massive targets (D-p/T < 1) are irregularly dist ributed on the witness plate, yet they organize into substantially con centric patterns as T decreases, including prominent ''hole-saw-rings' ' of craters that are remarkably constant in size, radial dispersion, and azimuthal separation. Components derived from very thin targets or ganize into radial streaks and projectile debris forms a centrally loc ated cluster of craters. Without exception, projectile debris dominate s the central plume portions and target-derived materials reside at th e periphery; as target thickness decreases, the spatial separation of these two components becomes increasingly prominent.