An Analysis of Surface Roughness and its Influence on a Thrust Bearing
Type of DegreePhD Dissertation
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Thrust bearings are a widely used type of bearing in many rotary industrial applications. In this work, a thrust bearing surface under the mixed lubrication regime is analyzed. A new model which coupled the mechanical deformation, thermo-elastic deformation, boundary lubrication and solid contact is developed to investigate the behavior of the thrust bearing during rotation. This new model provides predictions of important quantities such as the frictional torque, the load carrying capacity, the minimum film thickness, the temperature rise and the contact pressure. During the rotation of the thrust bearing in the mixed lubrication regime, surface asperities in the thrust bearing surfaces can come into contact to influence the properties of the thrust bearing. Therefore, the characterization of the rough surfaces is also very important in studying the thrust bearings. Fractal descriptions of rough surfaces are widely used in tribology. The fractal dimension, D, is an important parameter which has been regarded as instrument independent, although recent findings bring this into question. A thrust bearing is analyzed in the mixed lubrication regime while considering the multiscale roughness of its surfaces. Surface data obtained from a thrust bearing surface is characterized and used to calculate the fractal dimension value by the roughness-length method. Then these parameters are used to generate different rough surfaces via a filtering algorithm. By comparing the predicted performance between the measured surface and generated fractal surfaces, it is found that the fractal dimension must be used carefully when characterizing the tribological performance of rough surfaces, and other parameters need also be considered or found.