Research on Fatigue Crack Propagation Behavior of SMA490BW Steel for Bogie

The fatigue crack propagation behavior of SMA490BW steel for high speed bogie under different sampling orientation and stress ratio was investigated. The microstructure and fracture morphology of the samples were analyzed by optical microscopy and scanning electron microscopy. The results indicate that the fatigue crack propagation rates of the sample in T-L orientation and L-T orientation is basically the same. However, the stress ratio has remarkable influence on the fatigue crack propagation behavior. The fatigue crack growth rate under higher stress ratio is higher than that under lower stress ratio, which have significant influences on the near-threshold region and rapid growth region. The fatigue crack propagation threshold value ΔK_th under low stress ratio is higher than that under high stress ratio, which are mainly influenced by crack closure effect and the maximum stress intensity factor K_max.