Fracture mechanics assessment of crack propagation in railway axle steels under fully reversed variable amplitude loading

Application of fracture mechanics methods for predicting inspection intervals for wheelset axles requires, among other things, an accurate assessment of the level and sequence of service loads in the cross section subjected to examination. In order to characterize the crack propagation behaviour of typical railway axle materials such as 25CrMo4 (A4T) and 34CrNiMo6, tests on M(T) specimens have been performed under constant and variable amplitude loading conditions. The considered load spectra are derived from in-service measurements of stress amplitude histories of two different types of wheelset axles. A particular emphasis of the work is on the examination of crack growth acceleration and retardation phenomena arising under fully reversed loading (R = -1).