| Railway transportation based on wheel rail technology is still one of the most important ways in modern transportation.Wheel/rail contact force and fatigue damage have always been one of the main directions in the research field of wheel/rail technology.The surface profiles of wheel and rail are composed of straight segments and circular curves with different radii.The geometrical relationship and mechanics properties of contact are very complicated.At present,the research on wheel/rail contact mechanics performance is still not deep enough when the wheel is in the static state,the linear running state and the turning state,and the prediction of the wheel/rail rolling contact fatigue life has not come to a general model accepted by all people.Taking the standard LM tread wheel and rail CHN60 as the research object,the contact position of wheel and rail,the mechanics properties of wheel/rail contact and the rolling contact fatigue of wheel and rail are deeply studied in this dissertation.The main research contents and achievements of this dissertation include:(1)Based on the geometric analysis of wheel/rail contact,the contour equation of the wheel/rail surface is constructed.By solving the mathematical equations of the contour,a basic method is established to calculate the position of contact point with considering the rail cant,and the accurate calculation of the contact position of the wheel and rail is realized.By using MATLAB software programming,the variation of wheel/rail contact point with the relative position of wheel and rail is studied numerically when rail cant is 0,1:40 and 1:20.(2)The contact mechanics problem with curvature transition point in wheel/rail contact is studied.A "slice model" which can calculate the maximum normal stress and the size of contact spot in any shape is establshied.In this calculating model,the contour geometric interference is used to replace the contact deformation between wheel and rail,and the surface of the wheel is discretized into many thin slices.The stress and load of a single slice are calculated by the Hertz line contact theory.Through the correction of this calculating model,accurate calculation of the contact stress of the curvature transition points is realized.A case study is carried out for the specific working condition.A specific experimental device is designed and established to test the contact condition of two bodies when the curvature transition point exists in the contact surface.(3)Based on the method of calculating normal stress between the wheel and rail,the method of calculating normal stress,shear stress and the distribution of the adhesion and sliding zones in the wheel/rail contact spot on a straight line is established.Based on the theory of elastic mechanics,mechanics performance of contact body below the contact surface is calculated when the train runs in a straight line through the discretization of contact surface.With a specific example,the maximum normal stress,the maximum longitudinal shear stress and the longitudinal tangential load on wheel/rail contact surface on a straight line are obtained with the change of lateral displacement of wheelset.Distribution of Mises stress and maximum shear stress under wheel/rail contact surfaces at different wheel/rail relative positions is calculated.(4)A method for calculating and analyzing the internal and external mechanics properties of wheel/rail contact on a curve line is established Calculation of normal stress,shear stress and distribution of the stick slip area on wheel/rail contact surfaces on a curve section is realized by establishing the force analysis model on the curve section and combining the analysis of contact surface mechanics properties on the linear line.Calculation of the Mises stress and the maximum shear stress inside contact bodies is also achieved on the curve section.Through an example on the curve section,the stress of wheel/rail contact surface,Mises stress and the maximum shear stress in contact bodies are studied with the change of contact position.An example is taken to analyze the influences of train velocity,rail curvature radius,axle load,superelevation on the surface stress and internal stress of the wheel.(5)Randomness of wheel/rail contact is analyzed and determined.By discretizing wheel profile and using the normal distribution function,a method for calculating contact probability of each point on wheel surface is established.Combined with fatigue damage accumulation hypothesis and fatigue curve equation,the fatigue life damage and fatigue life prediction method for each contact point on wheel surface are established.A case study is carried out on a specific line,and the theoretical calculation of fatigue life for wheel/rail rolling contact is realized.The research content and achievements obtained in this dissertation can provide useful theoretical support for both the further study of wheel/rail contact and the prediction of wheel/rail rolling contact fatigue life. |
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