Expansion wave and cavitation bubble generation by underwater shock wave reflection from the interface

This paper reports an experimental result of expansion wave and cavitation bubble generation by underwater shock wave reflection at the interface for understanding of shock wave interaction phenomena related to the mechanism of shock wave human tissue damage. Underwater shock wave was generated by detonating a micro-explosive (silver azide pellet). The process of underwater shock wave reflection at the interface, expansion wave and cavitation bubble generation were visualized by shadowgraph method and recorded by an ultra-high-speed framing camera at high spatiotemporal resolution. The pressure time history near the interface in water was measured simultaneously by a needle hydrophone. High-speed shadowgraph sequential images show that a compression wave (shock wave) was reflected from a thin interface plate (Polystyrene, acrylic, Teflon, thickness of t=0.5 mm), and expansion wave was then generated in water by reflection from the air. In addition, a cavitation bubble was created behind the expansion wave. The simultaneously measured pressure history also shows that an expansion wave propagated behind shock wave. The negative peak pressure of expansion wave in the case of a thin plate shock wave interaction was larger than that in water surface interaction.