Towards three-dimensional characterization of hypervelocity impact events using ultrahigh-speed digital holography

Abstract

This experimental study reports the development and use of high-speed and ultrahigh-speed digital holography (DH) systems to perform three-dimensional (3D) characterization of particle-fields created from the impact of a supersonic projectile with a target plate. Different target materials including clay and gypsum were tested producing a cloud of ejecta particles from the impact zone. While the megahertz-rate ultrahigh-speed DH instrument version was used for measurements in early (0-250 µs) time-scale processes, the 100 kilohertz-rate high-speed version was employed to interrogate extended (250 µs-1 s) durations following impact. By capturing holograms and performing wavefront reconstruction at different depths, holography allows scanning through the 3D space plane-by-plane at given moment in time, allowing the user to focus on different objects to determine their shape and precise 3D location. We automate this particle detection procedure in sequential holograms by using a minimum intensity focusing criterion and obtain their locations in three-dimensional space with respect to time. Further, we track particles over these durations to determine their trajectories along with instantaneous and mean velocities. Based on the optical configuration and field-of-view employed both instruments were able characterize the ejecta clouds for particle size distributions ranging 1 µm-1 mm. The results presented clearly demonstrate the applicability of digital holography for 3D characterization of ejecta and debris clouds arising from the impact of supersonic and hypersonic projectile with different material targets.