Role of Bubble Collapse Pressure in Cavitation Erosion.

Abstract

A quantitative relation(F-N curve)was obtained betweent the constant impact load due to cavitation bubble collapse and the number of cycles to the incubation period termination. The relation was derived from the linear cumulative damage law, in which all impact loads including those of very low intensity(0.3 N)are assumed to cause damage. The slope of the F-N curve corresponds well with that of the S-N curve for a smooth specimen obtained from a standard fatigue test, provided that the contact area is obtained by the Hertz theory. The incubation period can be evaluated regardless of cavitation test conditions from the cumulative cycle ratio Σ(ni/Ni), using both the number ni of impact loads and Ni from an extrapolated F-N curve(modified Miner's law)for the corresponding impact load Fi. Similarly, the F-N' curve was obtained for the steady-state period, where N' was defined as the number of cycles required to achieve a mean depth of penetration(MDP) of 1 micron. The slope of the curve coincides well with that of the S-N curve for a slightly notched specimen. The Σ(ni/N'i)has a linear relation with the MDP in the steady-state period. Since N'i is proportional to 1/F2i from the F-N' curve, the cumulative cycle ratio was reduced to Σ F2i·ni, which is consistent with the impact energy from the authors' previous report. It is concluded that the ratios Σ(ni/Ni)and Σ(ni/N'i)are suitable parameters for evaluation of the cavitation damage in the incubation and steady-state periods, respectively.