Study on cavitation damage evolution influenced by input power

Cavitation damage, so called pitting damage, is one of crucial issues to predict the structural endurability of the mercury targets for highly intensive pulsed neutron sources. Experiments to systematically investigate the cavitation damage evolution on the surface in contact with the mercury have been carried out by using specially developed electroMagnetic IMpact Testing Machine (MIMTM) and then pit depth and equivalent diameter distributions in a certain damaged area of the specimen were measured in detail using a laser microscope. Pits with a maximum depth of less than 0.5 μm and an equivalent diameter of less than 5 μm were mainly observed. Based on the comparison with numerical simulation on the pit shape, the cavitation bubble collapsing was assumed to be resulted in the micro jet with the impact velocity of 160-200 m/s, imposing then impact pressure of 3-4 GPa at the input power simulating the operation condition in the mercury targets. As results, it was statistically understandable that cavitation damage evolution was proportional to 4th power of the input power approximately, as taking the aggressivity of cavitation bubbles and the distribution of the maximum diameter of grown bubbles and the space of distribution of bubbles in the mercury into account. (author)