Investigation on the Rolling Contact Fatigue Cracks Initiation of Subway Fixed Frogs Based on Transient Dynamics
The escalating traffic density and operational speeds of subway systems have intensified fatigue damage in turnout rails, particularly within the hazardous space of fixed frogs where wheel–rail dynamic interaction is exacerbated. This study addresses the rolling contact fatigue (RCF) crack initiation behavior of a No. 9 turnout fixed frog, a configuration widely deployed in subway networks. A three-dimensional explicit transient rolling contact finite element model was developed to simulate wheel–rail interaction under varying vehicle speeds and fastener vertical stiffness conditions. The analysis focused on crack initiation locations, angles, and fatigue life. Results demonstrate that the 30 mm top width cross-section of the nose rail is the most susceptible to fatigue cracking, with cracks initiating on the rail surface. The angle between the crack initiation surface and the lateral direction ranges from 70° to 95°, while the angle relative to the vertical direction remains difficult to predict. Higher vehicle speeds significantly reduce fatigue life, whereas fastener vertical stiffness exerts a minor influence. The calculated RCF crack initiation life is approximately 24,000 cycles across three stiffness conditions. Simulation outcomes align with field survey findings, validating the model's fidelity. The established methodology provides theoretical support for optimizing fixed frog structures and predicting fatigue life in subway turnouts.