Polygonisation is a common nonuniform wear phenomenon occurring in railway vehicle wheels and has a severe impact on the vehicle–track system, ride comfort, and lineside residents. This paper first summarizes periodic defects of the wheels, including wheel polygonisation and wheel corrugation, occurring in railways worldwide. Thereafter, the effects of wheel polygonisation on the wheel–rail interaction, noise and vibration, and fatigue failure of the vehicle and track components are reviewed. Based on the different causes, the formation mechanisms of periodic wheel defects are classified into three categories: (1) initial defects of wheels, (2) natural vibration of the vehicle–track system, and (3) thermoelastic instability. In addition, the simulation methods of wheel polygonisation evolution and countermeasures to mitigate wheel polygonisation are presented. Emphasis is given to the characteristics, effects, causes, and solutions of wheel polygonisation in metro vehicles, locomotives, and high-speed trains in China. Finally, the guidance is provided on further understanding the formation mechanisms, monitoring technology, and maintenance criterion of wheel polygonisation.

Out-of-roundness in railway wheels, in particular polygonal wear resulting in regular, multi-lobed, out-of-round wheels, has become a significant problem in recent years. It is of concern to railway operators due to the increased noise and vibration it can cause. This polygonisation is caused by cyclic wear but the exact mechanism leading to this type of wear is not fully understood. It appears to be the result of dynamic linking between a resonance or other periodic excitation in the coupled vehicle–track system and the existing wear at the wheel. This paper reviews the developing body of research being carried out in many countries by research groups, manufacturers and operators. Some examples of polygonisation on different types of railway vehicles are reported including feight trains, urban transit trains and high-speed trains. The main theories for the formation mechanisms are presented and the current measurement methods, computer simulation techniques and the effects and potential mitigation methods are reviewed. In parallel, the mechanisms and consequences of discrete wheel tread irregularities, such as wheel flats and material fall-out due to rolling contact fatigue cracking, are addressed.

This paper presents an investigation into the mechanism of polygonal wear of metro train wheels through experiments conducted at field sites. The experiments comprise dynamic behaviour test of vehicle and track system, the wheel transverse wear and polygonal wear measurements, rail corrugation and rail weld joint irregularities’ measurements. Moreover, the numerical modal analysis of the wheelset is also performed. The wheel measurement results show that most wheels exhibit obvious eccentricity and polygonal wear with 5–8 harmonics. The investigation results indicate that the wavelength-fixing mechanism of the wheel out-of-roundness with 5–8 harmonics is the P2 resonance. Four measures have been proposed to mitigate the formation of wheel polygonal wear based on the field measurement results.

Experiments were conducted at field sites to investigate the mechanism of the polygonal wear of electric locomotive wheels. The polygonal wear rule of electric locomotive wheels was obtained. Moreover, two on-track tests have been carried out to investigate the vibration characteristics of the electric locomotive's key components. The measurement results of wheels out-of-round show that most electric locomotive wheels exhibit polygonal wear. The main centre wavelength in the 1/3 octave bands is 200 mm and/or 160 mm. The test results of vibration characteristics indicate that the dominating frequency of the vertical acceleration measured on the axle box is approximately equal to the passing frequency of a polygonal wheel, and does not vary with the locomotive speed during the acceleration course. The wheelset modal analysis using the finite element method (FEM) indicates that the first bending resonant frequency of the wheelset is quite close to the main vibration frequency of the axle box. The FEM results are verified by the experimental modal analysis of the wheelset. Moreover, different plans were designed to verify whether the braking system and the locomotive's adhesion control have significant influence on the wheel polygon or not. The test results indicate that they are not responsible for the initiation of the wheel polygon. The first bending resonance of the wheelset is easy to be excited in the locomotive operation and it is the root cause of wheel polygon with centre wavelength of 200 mm in the 1/3 octave bands.

This paper presents a detailed investigation of out-of-round electric locomotive wheels through extensive measurement conducted at field sites. More than 2000 wheels, of seven types of locomotives widely used in China, have been measured since April 2013. The measurement results indicate that two types of freight traffic locomotives suffer serious polygonal wear problems with center wavelengths ranging from 160 to 315 mm. The dominating wavelength is 200 mm. Therefore, the investigations are mainly focused on the two locomotive types. The other types, which are taken for comparison, do not exhibit obvious polygonal wear. However, they exhibited more or less eccentricity. The effect of wheel re-profiling on the wheel polygon is also investigated and discussed. The dominating harmonic orders and center wavelengths after re-profiling are consistent with those before re-profiling at the correct circumstances, if the center wavelength of the polygonal wear is about 200 mm.

High-order polygonal wear wheels have been detected on metro express train operating on one metro line in China, which cause fatigue failures of steel coil springs in the primary suspension. A series of tests and theory analysis were conducted to figure out the mechanism of wheel high-order polygonal wear. The wheel out-of-roundness (OOR) measurement results show that the wheels exhibit polygonal wear with 12–14 harmonics, which are very different from other metro train wheels reported in the literature. The investigation results indicate that the first bending vibration of the wheelset is the root cause of wheel high-order polygonal wear. Rail corrugation with a wavelength of 200 mm in the 1/3-octave band on sharply curved tracks is the main excitation source of the first bending vibration of the wheelset. The formation process and key influencing factors of wheel high-order polygonal wear are analysed in detail. Three measures are suggested to mitigate the formation of wheel high-order polygonal wear.