Cavitation erosion incubation period

Abstract

To evaluate the "incubation period" (IP) stage of cavitation erosion, short-duration vibratory horn tests in tap water were made on soft aluminum alloy (aluminum alloy 1100-O) and also on a much more resistant alloy (316 stainless steel). Curves of weight loss versus time, and corresponding scanning electron microscopy photomicrographs taken during the IP, are presented and discussed. The effects of horn amplitude and temperature are investigated for "open-beaker" tests. The IP for 316 stainless steel is found to be about 500 times that for aluminum alloy 1100-O for the same amplitude and temperature. This ratio can be predicted almost exactly by applying an assumed relation between MDPRmax and IP, i.e. MDPRmax-1 = k(IP)n.Fatigue cracks and individual-blow craters were found for 316 stainless steel but only individual craters were found for aluminum alloy 1100-O, although their ductilities are approximately equal. It is found that the IP based on the eroded area only, IPerod, is much less than the conventional IP (based on the total specimen area) if IP is based on the attainment of a given mean depth of erosion MDP.Relations between the eventual erosion rate MDPRmax and the IP are considered. It is found that IP data can often be used to predict eventual MDPRmax values according to the relation MDPRmax-1 [is proportial to] (IP)n where n [approximate] 0.93 and n [approximate] 0.95 for our vibratory and Venturi data respectively. However, different values for n have been reported in the literature. By assuming a "characteristic" erosion-time curve the time of occurrence of MDPRmax can also be estimated.It is verified that only bubble collapse stresses are important in the vibratory horn test, although specimens are vibrated under very high accelerations.