| 520 |
|
|
|a A re-interpretation of recent RCF experiments by Clayton and Su (C&S) [Wear 200 (1996) 63] under water lubricated rolling/sliding conditions, with careful measurements of ratchetting strains, and their comparisons with experimentally observed lives, seems to confirm the validity of ratchetting failure (RF) mechanism and Kapoor's "critical ratchet strain" as a material property. However, the complexity of modelling the ratchetting phenomenon and the uncertainties on the material's critical ratchet strain, suggests that perhaps a more realistic alternative is the use of empirical Wöhler-like life curves similarly to currently used for the contact fatigue evaluation in gears design and standards. In particular, it is found that the "pitting" fatigue limit at 107 cycles suggested by the gears standard is reasonably accurate also for the C&S experiments on various typical rail steels. Since the gears life factor suggested for gears turns out quite conservative at shorter lives, it seems a single new life factor could be suggested, at least for all pearlitic and bainitic steels tested by C&S under water lubrication.
|
