Effect of mean stress on fretting fatigue strength at elevated temperature.

In order to investigate the effect of mean stress on fretting fatigue strength at elevated temperature, high-temperature fretting fatigue tests with various levels of mean stress were carried out using 12Cr-Mo-W-V steam turbine steel. The main results obtained are as follows. The fatigue strengths were decreased by fretting by a factor of three at both room and elevated temperatures regardless of the mean stress level. The modified Goodman relation held for fretting fatigue as well as for plain fatigue. The relationships between relative slip amplitude, friction coefficient and stress amplitude were independent of the mean stress level. The proposed method of fatigue life prediction based on fracture mechanics analysis, where the crack closure behavior was taken into consideration, was successfully applied to fretting fatigue with various levels of mean stress at elevated temperature.