Mechanisms of Railway Wheel Polygonization

  • Bo Peng

Student thesis: Doctoral Thesis


Railway wheel polygonization is manifest as uneven wear around the wheel circumference, which has been a severe problem worldwide for decades. It induces persistent periodic oscillation at the wheel-rail interface causing forced vibration to the vehicle/track dynamic system, which can seriously threaten the comfort and safety of the railway vehicles. Full understanding of its mechanisms is necessary for effective remedies to be proposed.

A Chinese electric locomotive suffering from severe wheel polygonization is employed as the research object. Abundant experimental data had been obtained by the CRRC Zhuzhou Locomotive Company through a long-term test campaign. With these measurement data, this dissertation aims to obtain general rules that the railway wheel polygonization will follow by simulation. The research is carried out in five fundamental aspects for railway wheel polygonization: the prediction program, the wear models, the effects, the influence of wheelset flexibility, and the influence of track flexibility. The main points of each aspect are described as follows.

(1) A common workflow for prediction of railway wheel polygonization is presented. Based on this workflow, some rules for the evolution of railway wheel polygonization are proposed providing innovative perspectives to understand the basic mechanisms of railway wheel polygonization. After summarising these rules, the general conditions for railway wheel polygonal wear to evolve are established. The phase between the instantaneous wear and the excitation is the key indicator determining the wheel OOR (Out-Of-Roundness) evolution direction (to grow or to diminish). The evolution tendency curve obtained from the instantaneous wear FRF (Frequency Response Function) is shown to be a useful tool for predicting the OOR evolution, especially for predicting the OOR order that would grow predominantly at a given operating speed.

(2) A comparative study on the applicability of existing popular wear models in simulation of railway wheel polygonization is carried out. Four representative wear models, developed by BRR (British Rail Research), KTH (Royal Institute of Technology), USFD (University of Sheffield), and Professor Zobory respectively, are selected for the comparison, with consideration of global and local methods. A uniform expression of the converted wear functions is derived analytically with the equivalent wear coefficient as a useful index to identify the proportional relationship between the wear models quantitatively. Simulation results show that all the wear models investigated present a similar ability to reflect the fluctuation of the instantaneous wear under various circumstances. Additionally, it is found that the global method is not suitable for calculating the polygonal wear of railway wheels.

(3) A tracking test for an electric locomotive suffering from serious wheel polygonization is introduced. Data is used to demonstrate the evolution of the polygonal wear of wheels and the vibration of the locomotive immediately before and after wheel re-profiling. A comparison is carried out between simulation results and measurement data. Based on the simulation model, parameter analysis is implemented to identify the effect of wheel polygonization on the dynamic performance of the vehicle quantitatively. Some general principles regarding the effect of wheel polygonization on the vehicle are derived.

(4) The influence of wheelset flexibility on wheel polygonization is investigated. Results show that the wheelset flexibility cannot dominate the railway wheel polygonization in a general sense, unless some prerequisites are fulfilled to provide a suitable environment for the wheelset flexibility to be effectively and continually excited to fluctuate the contact responses. The torsional mode of the wheelset can be effectively excited by stick-slip vibration due to saturated contact adhesion that can occur on track with small curve radii or by large traction torque. If this situation persists for a long time, the development of the wheel polygonization can be expected. The excited order will be exactly determined by the wheelset torsional modal frequency and the vehicle speed.

(5) The influence of track flexibility on wheel polygonization is investigated. The sleeper passing frequency and the P2 frequency are considered as the two dominant frequencies coming from the track flexibility. Although the sleeper passing frequency is the most dominant frequency coming from the flexible track, it will not produce visible development of wheel OOR. The P2 resonance is an important factor contributing to the development of wheel OOR. The local rail bending modes are not found to influence the wheel OOR based on the Simpack FTR method.
Date of Award2023
Original languageEnglish
SupervisorSimon Iwnicki (Co-Supervisor) & Phil Shackleton (Co-Supervisor)

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