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Fatigue property in gigacycle regime is focused as an important subject in recent years. In such a long-life region, a tremendous long period is required to perform the fatigue tests. In order to overcome this difficulty, special types of fatigue testing machines in rotating bending whose loading type is cantilever bending has been developed. It is known that this type of fatigue machine can be performed much quickly comparing with the tension and compression fatigue testing machines. And these experimental results are consistent with much data obtained by using traditional testing machines like tension and compression fatigue testing machines and the rotating bending fatigue test machines whose loading type is uniform bending named as Ono type, though it is unclear that much data of an ultrasonic fatigue testing machine are consistent with them. Although it prefers to perform the fatigue tests as fast as possible, but the maximum frequency of a rotating bending fatigue test are limited because of the possibility of temperature rise in specimen caused by the cyclic plastic work and the heat transfer from fatigue testing machine. Such local temperature rise might affect the fatigue property. However, the appropriate loading frequency limit is unclear because of the difficulty of the temperature measurement in the fracture portion of a specimen precisely during the rotating bending fatigue test. An in-situ temperature measuring technique is proposed to measure the temperature at the fracture portion of the specimen in real time during the fatigue testing, and the validity to determine the loading frequency of a rotating bending fatigue testing machine is discussed in this study. 1. 緒 言 金属材料の疲労試験は結果にばらつきが比較的多いことから,十分な数の試験結果を取得することが重要であ るが,広範囲の繰返し数範囲に対する S-N 曲線を得るためには長時間を要する問題がある.一方,近年,複数の 負荷条件に対して同時に疲労試験が可能である多連式回転曲げ疲労試験機(Yamamoto et al., 2011; Yamamoto et al., 2014; (株)山本金属製作所, 2015)が開発されており,同試験機を用いることで,引張圧縮疲労試験よりも高能 率に必要な試験結果を得られることが確認されている.一方,疲労試験期間の大幅な短縮という観点から近年そ の利用が拡大しつつある超音波疲労試験は,負荷方式が構造物や機器が実際に曝されている状況と異なることが 多いため,同試験方法を適用して得られた S-N 曲線を用いて疲労強度を評価してよいのかという点について,必 ずしも十分な理解が得られているとは言い難い面も残されている.また,超音波疲労試験では試験中に繰返し塑 Taizoh YAMAMOTO*1, Benning LIAN*1 and Koji GOTOH*2 *1 Yamamoto Metal Technos Co., Ltd. 2-4-7 Setoguchi, Hirano-ku, Osaka 547-0034, Japan *2 Kyushu University 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

The upper limit extension of loading frequency in the rotating bending fatigue test