Study on damage evaluation using cavitation-bubble collapsing time

Cavitation bubbles grow and collapse due to impulsive pressure change in liquids and the damage could be imposed on the interfaces between liquid and solid walls. Liquid heavy metals are applied as high-intensity spallation neutron sources, e.g., mercury targets in SNS (spallation neutron source in ORNL) and MLF/J-PARC, etc. The cavitation damage gets to be one of crucial issues from the viewpoint of structural integrity, i.e., durability under high power operation. The relationship between the dynamic behavior of cavitation bubbles and the local impact which generated at the cavitation collapse and causes the damage was systematically investigated using the direct visualization technique with a high-speed camera and electric spark thermal loading technique under water as comparing with the numerical simulation based on the Keller-Miksis equation. The results show a linear correlation between the impact energy of cavitation bubble collapse and the volume change of the bubble. In addition, this volume change can be evaluated from the collapsing time of the cavitation bubble. The collapsing time furthermore can be derived from the cavitation bubble development time using the simplified equation, and the local impact and damage due to cavitation collapse can be qualitatively estimated from bubble collapsing time.