Numerical study on temperature and thermomechanical rolling contact fatigue of polygonised wheel during tread braking

Wheel polygonization (polygonal wear) changes the wheel–rail contact and the wheel–brake shoe contact, which in turn changes the wheel temperature and the resulting rolling contact fatigue during tread braking. A simulation procedure based on the transient fully coupled thermomechanical finite element method is developed to investigate the response of the wheel material in the elastoplastic region, taking into account the synergistic effect of non-uniform thermal load and cyclic mechanical load due to wheel polygonization. The Dowling damage formula, Jiang–Sehitoglu fatigue model and Kapoor model are applied to investigate the rolling contact fatigue from the aspects of high cycle fatigue, low cycle fatigue and ratcheting failure, respectively. The temperature, stress–strain response, and fatigue pattern of a polygonised and a non-polygonised wheel during tread braking are compared. The simulation results show that wheel polygonization results in localized areas of low temperature at the troughs, while significantly higher temperature bands occur at the edges of contact hollows. Radial and circumferential compressive stresses and surface material flow increase as some stress–strain components tend to shakedown. Fatigue damage worsens especially at the polygonization crest, where the critical plane of crack initiation is more oblique to the axial direction and more towards the tread surface, while the ratcheting failure is attenuated. This research draws particular attention to polygonised wheels against excessive local temperature and rolling contact fatigue.