抄録
In this study, the fatigue tests for some engineering steels under the condition of stress rate R=-1 were conducted by the ultrasonic fatigue testing machine. The frequency of this machine was 20kHz. But net frequency f_<net> was lower than 20kHz. Because the intermittent operation with air cooling were conducted in order to suppress the heat generation by high speed test. The relationship between crack propagation rate and stress intensity factor range was compared with that of conventional fatigue test for low frequency (20kHz). The relation of ultrasonic was good agreement with that of conventional fatigue test. In-situ observation of a crack initiation and propagation was conducted. Striations were observed on the fatigue fracture surface.
