Effect of Residual Stresses on Safe Life Prediction of Railway Axles

Residual stresses play an important role in fatigue crack growth in railway axles. Due to crack closure, they affect not only the stress ratio R but add directly to the effective range of the cyclic crack load in terms of stress intensity factor. In order to account for this effect in a safe life analysis, the stress intensity factor KIrs due to the residual stress is required. The cut-compliance method is a suitable means to determine KIrs. The method is described briefly, and by an example it is shown how it can be applied to railway axles. The obtained residual stresses turned out to be compressive in the vicinity of the surface, which is beneficial for the fatigue performance of the axle. If these stresses are accounted for in the crack growth law, the calculated safe life in case of a pre-existing crack-like defect is increased dramatically. Furthermore, the effect of the press-fit of the wheels is investigated. The corresponding stresses were calculated by FEM. Actually, these stresses represent another type of residual stresses and can be superimposed to the measured residual stresses in the analysis. They also affect the crack growth rate significantly.