A New Microcontact Model Of Conformal Contact And Wear Life Prediction For Spherical Plain Bearings Based On Fractal Theory

The Spherical plain bearing are widely used in the critical part of the control and transmission system in the aerospace,wind power and high-speed trains(motor vehicles)because of their advantages such as: compact structure,low friction coefficient,impact resistance,safe and reliable,easy disassembly.So the study of lifetime prediction of the Spherical plain bearing has a crucial role on these equipments' structural design,maintenance planning,safety and reliability.In order to predict the lifetime of the Spherical plain bearing accurately,the failure mechanism and the wear rule of spherical plain bearing should be studied deeply.The wear of contact surfaces is the main reason for the failure of the Spherical plain bearing,and the wear of surfaces is actually the friction between asperities.In order to analyze the contact state of the spherical friction pair from a microscopic level more accurately,the fractal theory is introduced to study the contact state of the surface of Spherical plain bearing.The classical fractal contact theory only studied the contact between the plane and plane,so this paper proposes a conformal spherical fractal contact model,which can solve the same curvature contact problem.The lifetime calculation formula is established by combining spherical fractal theory with the structural characteristics of Spherical plain bearing.The research of this paper can provide the support for the wear analysis and lifetime prediction of the Spherical plain bearing.The main contents are as follows:1.The advantages and disadvantages of the GW fractal model?MB fractal model and YK fractal model are analyzed deeply,which can provide basis for the construction of spherical micro topography characterization.Three amended methods to calculate the fractal dimension which is the most critical parameter in fractal theory based on Power spectrum method,Structure function method and Variation method are proposed,these amended methods to calculate fractal dimension can greatly reduce the error brought by the traditional method,and many straight lines on cylindrical surface are measured,which validates the correctness of the amended methods.It provides a method to get the key parameter(fractal dimension)in the analysis of the micro topography of the spherical plain bearing.2.A method of characterizing the microscopic topography of rough spherical surface under the conformal contact based on fractal theory is proposed,the fractal contact model of the single asperity is further established based on the method.The macroscopic parameters and fractal parameters are introduced to construct the Contact Surface Coefficient,and the area distribution function that is suitable for conformal contact is obtained.Considering the frictional factor of the conformal contact region,the conformal spherical fractal contact model is established.The new model proposed by the paper is validated by numerical simulation.The new model solves the problem that the traditional Hertz contact theory can't be applied to the same curvature contact,and overcomes the limitation that the traditional fractal model can only be applied to the planes and the cylindrical surfaces.3.The spherical wear fractal model is established by combining the Archard model with the spherical fractal theory,and the model is validated by numerical simulation.The wear lifetime equations of the thrust bearing and radial spherical plain bearing are established by combining the spherical wear fractal model with the structural characteristics of the thrust bearing and radial spherical plain bearing.Finally,the lifetime equation is validated by comparing with the predicted results of SKF and the data measured by the experiment.The proposed life prediction formula considers the micro topography and contact state,so it can reflect the failure process of the spherical plain bearing more accurately,and the life prediction results are more reasonable.