Damage to the surface of railway wheels and rails commonly occurs in most railways. If not detected, it can result in rapid deterioration and possible failure of rolling stock and infrastructure components causing higher maintenance costs. This paper presents an investigation into the modelling and simulation of wheel flat and rail surface defects. A simplified mathematical model was developed and a series of experiments were carried out on a roller rig. Timefrequency analysis is a useful tool for identifying the content of a signal in the frequency domain without losing information about its time domain characteristics. Because of this it is widely used for dynamic system analysis and condition monitoring and has been used in this paper for the detection of wheel flats and rail surface defects. Three commonly used time-frequency analysis techniques: Short-Time-Fourier-Transform (STFT); Wigner-Ville Transform (WVT) and Wavelet Transform (WT) were investigated in this work.

This paper reports on fundamental research to investigate the influence of wheelset flexibility on the development of wheel polygonization of a locomotive. After preparing a flexible wheelset model by importing a FE (Finite Element) model into the MBS (Multi-Body System) environment, the investigation work proceeded in 3 steps. Firstly, FRF (Frequency Response Function) of the contact responses against the track irregularity is analysed for a free wheelset and an on-track wheelset, with consideration of rotation effect. Secondly, the influence of the wheelset flexibility on the contact responses excited by white noise is investigated for straight and curved tracks. The final step is to check the influence of the wheelset flexibility on the development of wheel polygonization based on a developed prediction program for railway wheel polygonization. 6 scenarios are investigated with comparison between rigid and flexible wheelsets. 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 in order to fluctuate the contact responses, and thereby initiate wheel polygonization. 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. In this case, the developed wheel polygonization order will be exactly determined by the wheelset torsional modal frequency and the vehicle speed.

This paper presents a comparative study on the applicability of existing popular wear models in simulation of railway wheel polygonalization. Four wear models developed by BRR (British Railway 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. All the wear models are firstly converted to calculate the instantaneous wear of one contact patch. A uniform expression of the converted wear functions is analytically derived, which allows a quantitative comparison between each wear model. Several scenarios grouped by simple excitation and complex excitation are adopted to assess the fluctuation of the instantaneous wear depth calculated by different wear models. The evolved polygonal wear around the wheel circumference is also compared among the wear models based on a developed prediction program. Simulation results show that all the wear models being investigated in this paper present a similar ability to reflect the fluctuation of the instantaneous wear under various circumstances. Specifically, the fluctuation of the instantaneous wear is obtained with almost the same results using different wear models with respect to the frequency and phase. While the mean value and the fluctuation amplitude of the instantaneous wear, as well as the roughness level of the evolved polygonal wear are all determined by the original wear coefficients used. The derived equivalent wear coefficient is a useful index to identify the proportional relationship among the wear models. Besides, the global method is believed not to be suitable for calculating the polygonal wear of railway wheels due to sharp corners probably generated by the absolute operation for the global WI (Wear Index).

The wheel-wear characteristics of the motor and unpowered car of a high-speed train were investigated, for the first time, by a wheel-wear prediction model comprising a wheel-wear submodel, an unpowered car dynamics sub-model, and a novel motorcar dynamics sub-model. The motorcar dynamics model considers the detailed structural characteristics and working mechanics of the traction transmission system. Assuming the real track parameters and track irregularities, it handles the nonlinear factors such as the traction characteristics, gear backlash, time-varying mesh stiffness, gear friction and wheel-rail contact. This study assessed the wheel-wear characteristics of a high-speed train by suitable performance indices (wheel-wear depth and contact patch energy). Finally, the model was validated by comparing the simulation results with those of field tests. The predicted and measured wheel wear were in good agreement. Both the wheel wear depth and contact energy were higher for the motor car than the unpowered car, because the traction torque on the wheelsets of the motor car increased the longitudinal creepage. During one re-profiling cycle, the transmission stability of the gear transmission system worsened with continuous wheel-wear. Furthermore, the proposed methods can assess the wheel wear and working status of the traction transmission system in the vehicle vibration environment of any rail vehicle.

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