Abstract
In order to develop an estimating method of fatigue damage caused by stress amplitude below fatigue limit, the present authors carried out several types of varying stress amplitude tests in the past. However, many of them were done at room temperature and only few investigations at elevated temperatures have been reported.
In the present study, repeated two-step varying stress amplitude tests which composed of a stress higher than the fatigue limit(overstress) and a stress lower than the fatigue limit(understress), were carried out on the smooth specimens of SUS 316, SCMV 4 and SCM 435 steels under rotating bending stress at temperatures up to 600°C. The fatigue data were analyzed by the Miner's and the modified Miner's laws, and the cumulative fatigue damage was discussed. The main results obtained are as follows:
(1) Under varying stress amplitudes, the understress gave a fatigue damage to the specimens and the cumulative fatigue damage calculated by Miner's law was less than unity.
(2) The modified Miner's law gave a conservative damage value for SUS 316 stainless steel at 600°C, although it gave poor damage values for SCMV 4 steel at 300°C and 500°C, and SCM 435 steel at 300°C.
