Effect of load frequency on high cycle fatigue strength of bullet train axle steel

A middle carbon steel is used for the axle of Japanese bullet train "Shinkansen". In order to clarify the effect of load frequency on the high cycle fatigue strength for this material, a series of high cycle fatigue tests were performed under the load frequency of 10 Hz, 400 Hz and 19.8 kHz up to 10⁹ cycles. As a result, the fatigue limit of tests performed at 10 Hz was almost equal to that of tests performed at 400 Hz, whereas that of tests performed at 19.8 kHz was much higher than that of tests performed at 10 Hz or 400 Hz. The increase of fatigue limit in tests performed at 19.8 kHz may be mainly due to the increase of lower yield strength by the rapid straining in an ultrasonic fatigue test. In addition, it seems that the fatigue limit for the cyclic softening material corresponds to the proportional limit in the cyclic stress-strain curve.