| During the Eleventh Five-Year Plan, the development of high speed railways of China has been a great success. With an increasing train speed, low adhesion between rail and wheel becomes more and more apparent. Surface damages on wheel-treads such as flats, skidding marks and shelling occur due to low adhesion. The study of the adhesion between the wheel and rail becomes one of the key technologies of improving the riding quality and safety. Thus the study of the adhesion between the wheel and rail is of significant theoretical and practical importance.The thesis first simulates a water or oil lubricated wheel/rail contact based on the full elastohydrodynamic lubrication (EHL) theory considering the real load between the rail and wheel and the real rail/wheel radius. The distributions of the liquid pressure and the film thickness are obtained using the EHL theory under the state of oil or water lubrication. The magnitude of the film thickness is determined. Second, partial elastohydrodynamic lubrication theory with Patir-Cheng's average flow model is used to model the characteristics of the adhesion between rail and wheel of the high speed rail vehicles taking surface roughness into consideration. To maintain the stability of the numerical calculation, Newton-Raphson method is used in the state of oil contamination. As the viscosity of water is low, multigrid method is used to study the state of water lubricated condition. The relationships between the speed, roughness, contact pressure, wheel radius and the adhesion of rail/wheel have been studied using the developed numerical model. In the end, comparisons are made for the adhesion coefficient under water and oil lubricated conditions at different speeds. The results explained the decrease of the adhesion coefficient. A simplified two dimensional line contact model is used to model the contact between the wheel and rail due to the difficuties of the adhesion theory and the numerical analysis.Several conclusions can be made according to the numerical simulation in this study:(1) The results of full lubrication show that the film thickness and the surface roughness are on the same level. The actual contact between wheel and rail is partial lubrication. Partial lubrication theory must be employed in the investigation of this problem.(2) The distributions of liquid pressure and pressure carried by solid and film thickness are obtained by partial EHL calculation. The distribution of pressure is different from Hertzian contact pressure. There is a spike near the outlet region under oil lubrication, which doesn't appear under water lubrication. Under oil lubrication the pressure carried by solid and film thickness like reflection relation. (3) The effects of speed on the adhesion under water and oil lubricated conditions are alike. With an increasing train speed, the adhesion between wheel and rail decreases. The decrease of the adhesion coefficient under water lubrication is greater than that under oil lubricated condition, which is the same as trend observed in the experimental test. Because the film thickness of water is larger than that of oil, the load carried by solid under water lubrication is much larger than that under oil lubrication.(4) With an increase surface roughness, the adhesion between wheel and rail increases under oil and water lubrication. The parameter of roughness orientation affects the adhesion coefficient. Under oil lubricated condition, when the roughness is transversly oriented, the nominal central film thickness is higher than the central film thickness when the roughness is longitudinally oriented. The adhesion coefficient shows a reversed relationship with respect to the roughness orientation.(5) With an increasing contact pressure, the adhesion between rail and wheel decreases gradually under water or oil lubrication. With an increasing wheel radius, the adhesion between rail and wheel increases gradually. |
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