Research on Wheel Polygonal Wear of Metro Vehicles Based on Wheel/Rail Vertical Coupling

Wheel polygonal wear is a critical form of non-uniform tread degradation in metro systems, leading to abnormal vibration, noise, and accelerated deterioration of wheel-rail components. This study aims to clarify the underlying mechanism of polygonal wear formation from the perspective of vehicle-track coupling dynamics. A comprehensive investigation combining field measurements, dynamic modelling, and finite element modal analysis is conducted. Field data reveal that polygonal wear is primarily concentrated in the 7~9th orders, corresponding to a dominant vibration frequency band of 50~70 Hz. A vertical vehicle-track coupling dynamic model is established to analyze the frequency response characteristics, while finite element models of different track structures are employed to identify intrinsic modal properties. The results indicate that the P2 resonance of the coupling system, occurring at approximately 63.36 Hz for floating slab track, closely coincides with the characteristic frequency of the 8th-order polygonal wear. This frequency matching condition leads to significant dynamic amplification at the wheel-rail interface, initiating initial geometric irregularities. Subsequently, a self-reinforcing feedback mechanism is formed, in which polygonal wear acts as a periodic excitation source that continuously excites the system near resonance. Meanwhile, local rail bending modes at higher frequencies further modulate the contact force distribution, promoting the growth and stabilization of polygonal patterns. In contrast, for trapezoidal sleeper track, the P2 resonance frequency shifts to approximately 126.91 Hz, which is significantly separated from the dominant excitation band. This frequency mismatch suppresses resonance amplification and inhibits the formation of low-order polygonal wear. In addition, it was found during investigation that periodic irregularities in rail joints are the external cause of wheel-rail P2 force resonance. These findings demonstrate that wheel polygonal wear is governed by a resonance-driven coupling mechanism controlled by frequency matching among track excitation, system resonance, and wear-induced vibration. The study provides a theoretical basis for vibration mitigation through track design optimization and wheel maintenance strategies.