Assessment of fatigue crack growth in metro cast manganese steel frogs and inspection strategy

Fatigue cracking is one of the notable failure mechanisms of railway turnout frogs due to high contact forces induced by the wheel-rail impact. However, the treatments specific to the frogs of cast high manganese steel to prevent sudden failure are rarely provided and are independent of the crack conditions, which can significantly affect the fatigue crack growth rate. To address this shortcoming, the fatigue crack growth in a cast high manganese steel frog is computationally investigated with varied wheel and crack conditions. The dynamic wheel-frog impact is first simulated to obtain the distribution of contact pressure imposed on the frog, and the propagation of the fatigue crack is then predicted using the finite element formulation in fracture mechanics. The simulation results show that the train speed and axle load can change the maximum contact stress. Nevertheless, when representing the growth rate in terms of the cumulative passing axle load, the effect of axle load and train speed on the crack growth is minimal and moderate, respectively. In contrast, the initial crack conditions, including the location and angle, have an overweighted influence. As a result, an inspection scheduling strategy for identified cracks with different conditions is proposed to consider both safety and operational efficiency.