On the prediction of high-cycle fretting fatigue strength: Theory of critical distances vs. hot-spot approach

This paper summarises the results we obtained when applying both the theory of critical distances (TCD) and the hot-spot approach to predict high-cycle fretting fatigue strength. In particular, the accuracy of such approaches was checked considering some experimental results taken from the literature and ad hoc generated to explicitly investigate the size effect in fretting fatigue. According to the well-known experimental outcome that initiation and initial growth of fretting fatigue cracks is mainly mixed-mode dominated, both the TCD and the hot-spot approach were used in conjunction with two different multiaxial fatigue criteria: the so-called modified Wöhler curve method (MWCM), that is, a conventional critical plane approach, and the well-known mesoscopic criterion due to Dang Van. Considering cylindrical-on-flat contacts tested under partial slip conditions, it was seen that the TCD is successful in predicting the size effect in fretting fatigue, resulting in more accurate predictions than those obtained by applying the classical hot-spot approach. Moreover, the present study revealed that the overall best accuracy is obtained when applying the TCD along with the MWCM. This result is very promising, especially in light of the fact that such a design methodology can be employed by simply post processing linear-elastic FE results, making it suitable for being used to assess real mechanical assemblies without the need for carrying out time-consuming elasto-plastic analyses.