Abstract
To improve fatigue strength and to reduce weight of a machine, surface treated materials are commonly used. Fatigue strength can be improved by the surface treatment, however, the estimation method of the fatigue life is not well established. To estimate a fatigue life, it is important to divide the fatigue life into crack initiatin life and crack extention life. In this study, a strain gage metod is proposed to detect a small crack initiation life accurately. Bending fatigue tests of round notched bar specimens with nitriding and with carburized quenching, and detect the small crack initiation with this method to find the difference of the fatigue crack initiation and propagation behaviors.
