A HIGH-SPEED PHOTOGRAPHIC STUDY OF CAVITATION DAMAGE

Cylindrical cavities, viewed through the side as they collapsed onto s olid surfaces, were studied using high-speed streak and framing photog raphy. The cavities were collapsed asymmetrically using shock waves of varying amplitude so that the rear surface formed a high-speed jet wh ich crossed the cavity and interacted with the target surface. Schlier en optics were used to visualise waves in the fluid and in the target. Two features of the collapsing bubble affected the damage to the targ et surface. The first was the impact of the high-speed liquid jet on e ither the rear wall of the cavity or the target itself. The second was the production of a strong compression wave on the rebound of the bub ble after it reached minimum volume. Damage to the targets related to their material properties. Metals, with low compressive but higher ten sile strengths, plastically deformed beneath the penetrating jet to fo rm a pit. Brittle materials, with high compressive but low tensile str engths, deformed by cracking. The position of the cavity relative to t he surface had a major effect upon the geometry of the damage. With th e cavity close to the target, the penetrating jet dominated the damage leaving single pits. With the cavity at some distance, the rebound wa ve was more important than the jet giving rise to a circular damage ma rk. This mechanism can be used to re-interpret previous experimental o bservations [Y. Tomita and A. Shima, J. Fluid Mech. 119, 535(1986)]. ( C) 1995 American Institute of Physics,