A novel method for evaluating wheel-flat dimensions under braking in railway vehicles

A coupled numerical analysis framework combining vehicle-dynamics simulation using the commercial multibody software SIMPACK with wheel–rail frictional-thermal analysis was developed to elucidate the mechanisms governing wheel-flat initiation and growth during braking. This framework integrates dynamic wheel–rail interaction, transient frictional heating, the temperature-dependent yield stress of wheel steel, and a geometrically derived expansion law of the contact ellipse to quantitatively predict wheel-flat dimensions under locked-wheel conditions. A one-way coupled analysis enables efficient computation while retaining the physical fidelity required to reproduce thermomechanical deformation at the wheel–rail contact interface. Validation using measured data from an in-service commuter train demonstrated that the predicted wheel-flat dimensions agreed with observations within approximately 10%, confirming the reliability of the model. A parametric study revealed that wheel-flat growth is strongly influenced by the initial braking velocity, the wheel–rail friction coefficient, and the lateral motion of the wheelset induced by vehicle dynamics. The proposed numerical analysis framework provides a practical tool for predicting wheel-flat behaviour under realistic operating conditions and offers insights for developing improved wheel-flat prevention and mitigation strategies.