Study On The Mechanism Of Rail Corrugation On Subway Track

Rail corrugation has excited the interest of railway researchers for more than a century. But there is not a good cure for it. It has been realized that different type of corrugation arises from different mechanism, and some types of corrugation can indeed be prevented through proper method. Now, rail corrugation appears on many metro lines. The mechanism of subway rail corrugation is complex and it is still not fully understood. Its research involves many subjects and multi-field knowledges, such as structural dynamics, rolling contact theory, tribology, material science, computational method, etc. Therefore, it is very important to carry out in-depth research on rail corrugation in metro system so as to understand the formation mechanism and then propose the corresponding mitigation measures, which is of great significance for ensuring the safe operation of metro vehicles and urban railway noise and vibration reduction.Rail corrugation has caused serious problems on a Metro line shortly after the operation, which not only caused strong vibration of the vehicle and track, but also brought annoying ambient noise, and aroused strong dissatisfaction of passengers and nearby residents. Aiming at investigating the formation mechanism and mitigation measurements of rail corrugation, the present paper conducts a detailed study on the following aspects.(1) A brief overview of the development of urban rail transit and the accompanied corrugation problem is presented. The studies on subway corrugation are reviewed in detail. The importance of study on rail corrugation is pointed out.(2) The thesis gives a detailed description of the characteristics of vehicle-track structure of the selected Metro line, rail corrugation on the typical sections, and obtained test results of track structure. The relationship between the natural frequencies of the track structure and the passing-frequencies of the existing corrugations is investigated. It shows that the corrugation occurrence has nothing to do with the wheelset twist resonance and mainly corresponds to the characteristic of the track structure.(3) The3D FEM mod is developed. The model considers the coupling effect of the vehicle unsprung mass and the track structure. Using the model finds the relationship between the mode shapes and the corresponding resonance frequencies of the track structure and the corrugations. The preliminary explanation of the formation mechanism of corrugation on different track structure is presented.(4) A rail corrugation model for the metro vehicle and the slab track is developed. It considers a combination of the coupling dynamics model of a whole vehicle and track, the modified Kalker’s non-Hertzian rolling contact model for wheel and rail, a material wear model and a accumulated wear model. It considers not only the effect of wheel/rail transient dynamic interaction on the formation and development of corrugation, but also the effect of the accumulated corrugation on the wheel/rail contact and coupling dynamics. That is, this model can take into account a feedback process between the long-term effects of the rail corrugation and the transient coupling dynamic of whole vehicle. In the coupling dynamic model, the vehicle is treated as a full rigid multi-body system; the rail is modeled with a Timoshenko beam resting on discrete rail pads. The slab is modeled as a three-dimensional flexible structure based on finite element method. The effect of the accumulated corrugation on the wheel/rail contact is considered in rolling contact model. The material model is based on the frictional work which considers the spin effect. The accumulated wear model can superimpose the corrugation formed due to the interaction between the8wheels of the whole vehicle and the rails.(5) Extensive filed measurements of rail corrugation are carried out and analyzed in detail. The developed corrugation model is validated by using the tracking test results and the validation shows a good agreement between the results of the test and the calculation by the model.(6) The formation and development mechanism of corrugation on the tracks with fix-dual short sleepers and Cologne fastenings is investigated through the numerical simulation which calculates the response of the wheel/rail system to the excitations of white noise, mixed-sin irregularities and dent defect. The obtained results are as follows:①the resonant in the band of60Hz-90Hz of the fix-dual short sleepers track is an underlying cause of the125mm-160mm wavelength corrugation, and indicates that the rail together with the slab vibrates with respect to the subgrade in vertical direction.②the resonant in the band of160Hz-300Hz of the Cologne fastenings track is the root cause of the40mm-50mm wavelength corrugation. The resonant includes the vertical bending vibration and the torsional vibration of the rail, with respect to the slab.③the calculated wavelengths of corrugation are consistent with the measured results.④the formation of corrugation is mainly influenced by the inherent characteristics of track structure and vehicle speed.⑤the track irregularities can develop into rail corrugations only when the passing frequencies of their wavelengths are close to the frequencies of the track resonances to be easily excited. Otherwise, they will disappear gradually in the wheel/rail rolling contact process.(7) The effect of fastener parameter, curve superelevation, vehicle load and friction coefficient on the rail corrugation formation is also investigated through the numerical simulation, and the corresponding mitigation methods are proposed. The numerical results show that with the increase of fastener parameter the sensitive resonance frequencies of the Cologne track are changed and the fluctuating amplitude at the passing frequency of the corrugation significantly decrease and the development speed of the corrugation is quite slow. An appropriate reduction in the superelevation can slow down the formation and development rate of corrugation. When passing over the corrugated rail, the vehicle in non-peak results in larger non-uniform wear compared to the vehicle in peak, that is, the corrugation resulting from the vehicle in non-peak is more serious. On the premise of ensuring the braking and traction requirements, the friction coefficient less than0.35can effectively controls the development of rail corrugation.