Probabilistic fatigue S–N curves including the super-long life regime of a railway axle steel

A concurrent probability method is proposed for estimating probabilistic fatigue S–N curves including the super-long life regime. This work is based on experimental investigation of LZ50 railway axle steel. Test results reveal that fatigue cracks are initiated from the weakest surface phase and the damage preferentially follows a competition mechanism between the surface quality and subsurface inclusions. The curves are estimated by the test data in the mid-long life regime and the fatigue limits, which were connected together in concurrent probability levels. The accuracy of the curves was verified by the test data in the super-long life regime.