1987 Fiscal Year Final Research Report Summary

Fundamental Studies on the Estimation of Cavitation Erosion

Research Project

Project/Area Number	61460082
Research Category	Grant-in-Aid for General Scientific Research (B)
Allocation Type	Single-year Grants
Research Field	機械材料工学
Research Institution	Fukui University
Principal Investigator	OKADA Tsunenori Fukui University, Dept.of Mechanical Engineering, Professor, 工学部, 教授 (40020185)
Co-Investigator(Kenkyū-buntansha)	HATTORI Shuji Fukui University, Dept.of Mechanical Engineering, Research Associate, 工学部, 助手 (00143933) IWAI Yoshiro Fukui University, Dept.of Mechanical Engineering, Associate Professor, 工学部, 助教授 (40115291)
Project Period (FY)	1986 – 1987
Keywords	Cavitation / Bubble Collapse / Impact load / Critical Pulse Height / Cavitation Erosion / Erosion Pit / Damage Estimation System / 直線疲労被害則 / 浸食試験方式 / 浸食面形状解析システム
Research Abstract	Cavitation damages were studied by both the measurements of cavitation bubble collapse pressures (impact loads) using our developed method with a piezoelectric detector and the cavitation erosion tests. The magnitude of impact loads produced by bubble collapses fractuates in the wide range in a magnetostrictive vibratory facility. There exists a lower critical impact load which contributes to fatigue fracture of surface. This value becomes higher for harder materials in Al, Cu and steel but scarecely increases with the tensile strength for steels. The lower critical impact load is larger in a high water based fluid (HWBF) than ion exchanged water due to the improvement of fatigue strength of the material. Thus, the detachment of erosion particles are prevented, resulting to decrease of cavitation damage in HWBF. When we consider that the lower critical pulse height(impact load) corresponds to fatigue limit of the material, the distributions of impact load are compared with the asuumed S- N curves of fatigue. As a result, Miner's law is realized for the incubation period and the reciprocal of volume loss rate during the stationary stage regardless of the cavitation conditions and the materials. The cavitation bubble collapse pressures in a flowing system were also studied. In a venturi facility, the generating number of impact pulses is very small but impact pulses to form a erosion pit impulsively are considerably large compared with the results obtained by a vibratory facility. In a rotating disk facility, the erosion depends on the fatigue fracture caused by the repeated action of the small collapse pressures below the lower critical pressure which forms a erosion pit. From these results, it is concluded that erosion loss can be estimated quantitatively from the distributions of bubble collapse pressures and lower critical pressure of material.