高強度ステンレス鋼SUS630の超高サイクル疲労強度とき裂進展特性に及ぼす応力比の影響

抄録

Since SUS630 is good at strength and anticorrosion, it is used for a wide range of engineering fields, where high reliability is required for the material. Along with the aging of structural components, fatigue strength and fatigue crack growth characteristics are becoming more significant in very high cycle regime. In this study, crack growth tests were conducted using ultrasonic fatigue testing machine in order to clarify the effect of stress ratio on the crack growth characteristics of SUS630. The crack growth test results show that stress ratio have strong influence on threshold characteristics and that the crack growth rate of stress ratio, R, of 0.8 is higher than those of other R. The characteristics were compared with a standard, WES2805, published by The Japan Welding Engineering Society. Fatigue crack growth diagram of WES2805 showed conservative crack growth characteristics compared with the experimental data. Ultrasonic fatigue tests were also conducted for sharp notched round bar specimens. The fatigue test results revealed that the threshold stress intensity factor range calculated by tensile component of the cyclic stress and the notch depth regarded as a crack length is a controlling parameter for the fatigue fracture of the sharply notched specimens. Maximum stress intensity factor at fatigue limit and threshold stress intensity factor range at R of 0.5 showed similar values due to the crack closure behavior.