人工キャビテーション壊食を付与したステンレス鋳鋼水車ランナSCS5の疲労強度特性

概要

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In hydraulic turbine runners, accidents due to cyclic loading often occur. In this study, bending fatigue tests were carried out for the stainless cast steel SCS5 cut out from the hydraulic turbine runner vane used for 22 years, in order to clarify fatigue properties and fracture mechanism of SCS5 with artificial cavitation eroded surface. The test results are summarized as follows : (1)The fatigue strength of the specimen with artificial shallow cavitation eroded surface was higher than the specimen data cut out from vane inside. In the meanwhile, hole shape and uniformity part of artificial cavitation eroded surface was smaller than the specimen data cut out from that. (2)From SEM observation of the fracture surfaces, crack initiation sites were found to be the cavitation eroded surface and the casting defect which consist of dendritic phase and pore. (3)It is possible to evaluate the fatigue life of cavitation eroded hole shape by using stress concentration factor. (4)It is possible to evaluate the fatigue life of aged SCS5 by using the defect size √area and the initial stress intensity factor calculated by cavitation damage size and casting defect size. The value of the threshold stress intensity factor of cavitation eroded surface obtained in this study were 5.3 MPa·m1/2.