Study On The Mechanism Of Rail Corrugation On High-speed Railway Unballasted Track

Corrugation is a wave-like periodical wear along the running band of rails due to the nonuniform wear of the rail surface. Although corrugation has been studied nearly a century, it remains a open scientific problem because of its complications. The study of corrugation involves knowledge from material science, tribology, structural dynamics,rolling contact theory, contact mechanics, and numerical analysis. Corrugation increases wheel/rail interaction force, enlarges vibration and noise of vehicle and track,deteriorates riding comfort, shortens service life of parts on vehicle or track, and affects operation safety.Corrugation has been found on some rails of China's high-speed railways after being put into service. The corrugation on high-speed railways not only causes high frequency vibration, but induces potential operation safety problems. However, the development characteristics, the forming mechanisms, and the influence on vehicle and track of the corrugation on China's ballastless track of high-speed railways have not been systematically studied. Thus an in-depth study on the corrugation on ballastless high-speed track and its mechanisms is of theoretical and practical significance on raising the operation safety and riding comfort and lowering the operation cost of the high-speed railways.This dissertation studies the corrugation on China's high-speed railways,the causes,and its influence on the high-speed vehicle and track, which includes:(1) The corrugation status of a high-speed line was systematically monitored, the development of corrugation according to time and location on the track was analyzed,the characteristics of corrugation development on different track conditions were summarized. It is found that, on the investigated high-speed railway, the main wavelengths of rail corrugation are 65-80 mm and 125-160 mm. Corrugation exists on straight sections, spiral curve sections and round curve sections of the track. On curves,low rails corrugated more severe than high rails. Corrugation grows fast at its initiation but slows down with its development. Rail grinding can effectively alleviate corrugation but it comes back not long after grinding.(2) The vibration characteristics of the ballastless high-speed track was measured and the correlation between the vibration characteristic and corrugation was analyzed. A three dimensional finite element model of the ballastless high-speed track was established and used to study the effect of track vibration characteristics to the corrugation according to modal response analysis, frequency analysis, and wide frequency range excitation-response analysis. Both experimentation and simulation results show that the 65-80 mm wavelength corrugation is related to the vertical pinned-pinned resonance of the track at about 1000 Hz due to the discrete supported rail and the 125-160 mm wavelength corrugation is related to the vertical vibration of the rail with respect to the track. It is found that increasing the stiffness of rail fasteners can effectively alleviate the 125-160 mm corrugation.(3) The mechanism of the initiation and development of corrugation on ballastless high-speed track was investigated. The correlation of rail irregularity and decarburized layer with the rail corrugation was investigated. Based on vehicle-ballastless track dynamics, wheel/rail Hertian contact theory, Carter rolling contact model and wear model of wheel/rail materials, a numerical model that can reflect the effects of decarburized layer to the rail corrugation was established, numerical simulation of rail corrugation under the effects of decarburized layer was conducted. It is found that the initial rail irregularity is important to the growth of rail corrugation. When the rail surface has an initial irregularity with the same wavelength of corrugation, rail corrugation grows rapidly; But if the wavelength of rail initial irregularity is different from that of corrugation, the rail corrugation grows slowly or even does not grow.Thicker decarburized layer results in a lower rail surface hardness and wear resistance,thus leads to a more severe corrugation.(4) The influence of corrugation on the high-speed vehicle and track was investigated. Using the measured corrugation as the system excitation source, a vehicle-ballastless track dynamic model was established and used to simulate the effects of corrugation on high-speed vehicle and track. The results show that the more severe corrugation results in a stronger wheel/rail interaction, a larger wheel/rail vertical force and a larger derailment coefficient. With an increasing corrugation peak-to-valley depth,the vibration of parts on high-speed vehicle becomes larger, however this influence decreases along wheelsets, bogie frame, and car body. When the high-speed vehicle is running over corrugated rails, the fastener force shows a high frequency oscillation, the value of the maximum fastener force increases significantly.