抄録
In this study, an ultrasonic torsional fatigue testing machine was developed in order to investigate the very high cycle fatigue properties of carburized steels. The testing machine can apply more than 800MPa of shear stress amplitude at 18.3kHz. The very high cycle fatigue diagram and crack propagation behavior of carburized SCM420H were obtained by using the testing machine and compared with results of non-carburized SCM420H. Fatigue crack initiation and growth was observed in very high cycle regime for both carburized and non-carburized SCM420H. It was found that carburizing of SCM420H was effective to enhance the fatigue life in very high cycle regime. In addition, crack deflection from mode II to mode I under torsional fatigue was discussed based on the fracture mechanics.
