Investigation on the Rolling Contact Fatigue Cracks Initiation of Subway Fixed Frogs Based on Transient Dynamics

• • The 30 mm top width cross-section of the nose rail is identified as the critical fatigue-prone zone, with crack initiation occurring on the rail surface. This localization enables targeted inspection and maintenance protocols, potentially reducing unplanned track failures by focusing non-destructive testing on this specific geometric region. • • Crack initiation angles relative to the lateral direction range from 70° to 95°, while vertical orientation angles remain unpredictable. This angular constraint provides a quantitative basis for designing crack-arresting features or surface treatments, as the predominant lateral orientation governs the stress intensity factor driving crack propagation. • • Increasing fastener vertical stiffness slightly amplifies wheel–rail impact response, but the effect is marginal. The calculated RCF crack initiation life is approximately 24,000 cycles under three different stiffness conditions, indicating that fastener stiffness optimization alone cannot substantially extend frog service life, necessitating alternative mitigation strategies. • • Higher vehicle speeds result in shorter fatigue life, establishing a direct operational trade-off between subway speed increases and turnout component durability. This speed-dependent degradation rate must be incorporated into maintenance scheduling and speed restriction policies to prevent accelerated crack initiation in fixed frogs.