High-speed image-forming instrumentation for hypervelocity impact studies

Abstract

Fast image-forming instrumentation is, by far, the most widely used means for studying hypervelocity impacts when time-resolved information is sought. Single frame (snapshot) cameras are available whose exposure times are short enough to effectively “freeze” material movements in even the fastest impact events. Flash X-radiography equipment is available for taking “snapshot” silhouettes through smoke/dust that defeat visible-light cameras. Similar X-ray equipment operating at higher voltage allows taking flash radiographs through massive materials so that internal features of impacts can be observed. A second series of imaging techniques take cine' sequences of photographs of dynamic events analogous to conventional motion-picture photography. Currently, available equipment operating in the visible is fast enough to time-resolve almost any conceivable macro-impact. X-ray cine' equipment is available, but it is in a considerably earlier stage of development. Streak photography has found wide use in the shock wave analysis community and has also been applied successfully to diagnosing hypervelocity impacts. Streak cameras produce position-vs.-time plots of visualized events that occur along a pre-selected line across the image of an impact process. To the author's knowledge, streak photography has been applied to ballistic research applications exclusively in the visual spectral region … although appropriate energy sources and electronic streak cameras for operating in the X-ray spectral regime have been available for at least a decade.