HIGH-SPEED OBSERVATIONS OF THE VIBRATORY CAVITATION ACCOMPANYING HARDEROSION

In this paper, the term ''hard erosion'' refers to erosion which is fa ster than ordinary erosion by a factor of two or more. Here, we carefu lly observe cavitation aspects of several types and the corresponding eroded surfaces in typically accelerating vibratory erosion tests on a typical erosion-resistant material of 304 stainless steel by means of high-speed and SEM photography, under a specified condition of unifor m cavitation nuclei size distributions. Hard erosion clearly results f rom very high shock pressures accompanied not by microjet bubbles or b ubble clusters, but by collapsing massive bubbles. The massive bubbles very rapidly develop within the low-pressure region where the Hooper vortex is predominant around the test specimen, and then collapse, res ulting in marked shock waves by which almost all of the tiny bubbles a re destroyed.