Fracture mechanics assessment of railway axles based on experimental and computational investigations

In this paper the results of the ongoing joint research project - Safe and Economic Operation of Running Gears - aiming at developing validated fracture mechanics assessment procedures for railway axles are presented. The paper includes material characterisation for the commonly used axle steel 25CrMo4 (A4T) and the high strength steel 34CrNiMo6. Fatigue crack growth parameters are experimentally determined both in the range of stable crack propagation and near the threshold. The results are employed for predicting fatigue crack growth for cracks initiating at the axle shaft. For the computational modelling of fatigue crack propagation a generally applicable solution for stress intensity factors has been derived. Furthermore, the influence of variable amplitude loading (block loading) on the crack propagation behaviour has been studied and is discussed. The computational results are compared with experimental data determined on standard fracture mechanics specimens as w ell as down-scaled and geometrically similar axle specimens.