On ratchetting-based models of wear and rolling contact fatigue (RCF)

Recent efforts to develop simple unified models of both wear and rolling contact fatigue (Kapoor et al. [1], Franklin et al. [2]) are discussed, in view of previous theoretical and experimental results on ratchetting in rolling contact. It is shown that ratchetting in rolling contact is a combination of "structural ratchetting" (that modelled with the perfect plasticity model) and "material ratchetting", and the latter is very sensitive to the hardening behaviour of the material. Also, rolling contact fatigue at large number of cycles in the Clayton and Su experiments [3, 41 seems not well correlated with shakedown theory, and accordingly, simple ratchetting equations based on excess of shakedown such as that of Tyfoor et al. [5], do not seem well suited as a Wohler SN life curve. However, these conclusions are only very qualitative as the materials in the two tests are different, and at present empirical separate models for wear and rolling contact fatigue based on hardness of materials and a posteriori data fitting seem the only quantitative way forward for engineering purposes.