Fracture mechanics assesssment of crack propagation behaviour in railway axles

Railway axles are safety relevant components which in some cases are designed for thirty years of service. Besides the experienced based definition of inspection intervals the application of fracture mechanics tools is currently being introduced as an appropriate method. Basic fatigue crack growth data both in the range of stable crack propagation and near the threshold have been experimentally derived for the widely used heat-treated railway axle steel 25CrMo4 (EA4T) under constant amplitude loading at relevant stress ratios (predominantly fully reversed load cycles, R = -1). For the computational modeling of fatigue crack propagation generally applicable solutions for stress intensity factors have been derived by FE analyses. The results are employed for predicting fatigue crack growth for cracks initiating in the axle shaft. However, the methodology may also be applied to fillets (transition radii). Additionally important aspects influencing the crack propagation behaviour in the vicinity of press-fits are discussed.