Mean stress effects in fretting fatigue life estimation method using fatigue damage gradient correction factor

Abstract

In our previous study, we developed a fretting fatigue life estimation method that considers stress gradient effect [Journal of Mechanical Science and Technology 28 (2014) 2153-2159]. In this method, fatigue damage value at the cracking location is corrected with the factor that is a function of fatigue damage gradient, and the corrected value is treated as the fatigue damage value in plain fatigue for life estimation. In the present study, we examined the effect of mean stress on fatigue damage gradient correction function, because the reliability of the developed method was only verified at a stress ratio (R) of -1 in previous studies. Fretting fatigue experiments were conducted to obtain the fatigue life data of three different fretting pad shapes with R values ranging from -1.0 to 0.3. Finite element analyses were then conducted to evaluate the fatigue damage parameter in the cracking region. The results revealed that fretting fatigue life decreases at increased stress ratio. Furthermore, the fatigue damage gradient correction function was unaffected by the stress ratio, although it is affected by plastic deformation at the cracking location. Thus, a correction function for the occurrence of plastic deformation and another for the absence of plastic deformation are necessary. The developed method was demonstrated to predict the fretting fatigue life at various levels of stress ratio with the use of plain fatigue data.