An approach to determine a critical size for rolling contact fatigue initiating from rail surface defects

A methodology for the determination of a critical size of surface defects, above which RCF can initiate, has been developed and demonstrated with its application to the passive type of squats under typical Dutch railway loading conditions. Such a methodology is based on stress evaluation of transient rolling contact at the defects, for which a detailed 3D frictional rolling contact model is integrated in the vehicle–track interaction system. Through comparing the maximal von Mises stress at defects of different sizes with the tensile strength of the rail material, the critical size is derived for squats. Observations during a field monitoring test show a good validation of the determined critical size. In practice, the critical size can be used for distinguishing between light squats and trivial defects by visual inspection or by automatic image recognition, so that false statistics of squats can be reduced or prevented. With necessary modifications and improvements, the developed methodology may also be applied to RCF of other rolling contact pairs in general, such as bearings and gears.