Influences of Foreign Object Damage on Fatigue Strength of 25CrMo4 Axle Alloy Steel

To study the correlation between the foreign object damage (FOD) and the fatigue strengh of alloy steel 25CrMo4, the simulated test for FOD of high speed railway axle steel specimens was carried out by a compressed-gas gun device. Firstly, the FOD defects were simulated on railway axle steel specimen surfaces. Secondly, the fatiuge S-N curves of smooth and FOD specimens were obtained from rotating bending fatigue tests. Furthermore, the stress concentration factor was evaluated for different types of defects by elastic finite element method (FEM). The fatigue limit and fatigue notch coefficient (FNC) of FOD specimens were calculated based on Peterson formula. The results show that the fatigue performance of FOD specimens is considerably lower than that of smoothed ones, the higher the impact velocity, the lower the fatigue performance. The FNC of edge defect specimens is the largest (about 1.52) while the smallest (about 1.14) for plane defect specimens, thus leading to a larger dispersion in lifetime. Compared with the experiments, theoretical evaluation and FEM method can obtain relatively conservative results in fatigue strength.