Characteristic analysis of journal bearing under thin film lubrication—Layered Viscosity Model
Journal bearing is a kind of widely used bearing and its study never stops. The analysis is carried to journal bearing with layered viscosity model in this paper. Layered Viscosity Model regards viscosity as piecewise function and averages every segment in order to get more accurate expression, and the pressure distributing, load capacity and friction are obtained for journal sliding bearing under thin film lubrication. The condition of thin film lubrication actualizing is made certain. The theoretical base is provided for the analysis of aggradation and liniment surface layer lubrication. This work could promote the understanding and research of the mechanism of the nano - scale thin film lubrication.
Rheological Models for Thin Film EHL Contacts
Rheological behavior in concentrated contacts has been studied extensively. In certain conditions such as a rough concentrated contact or sliding of nominally flat surfaces, films may be of molecular (nanometer) scale. The question arises as to whether the application of any viscous fluid model is appropriate. In this study, elastohydrodynamic lubrication analysis is performed on three candidate rheological models: (1) the classical case of viscosity variation with pressure, (2) an isoviscous model which idealizes porous layers on the solid surfaces representing the molecular microstructure, and (3) an isoviscous model which includes van der Waals and solvation surface forces. The latter two models predict behavior similar to classical behavior. The study is not sufficiently sensitive to determine which model best predicts experimental results, but some credence must be given to the latter two because experimental evidence suggests that Reynolds' equation is not valid for molecularly thin films
The Effects of a Stationary Surface Pocket on EHL Line Contact Start-Up
In this paper, the start-up process of line contact elastohydrodynamic lubrication with a stationary central surface pocket is studied. The solution of the pressure profile and film thickness distribution in the contact area is achieved by using a mixed lubricated-solid contact model. The mass balance of pocket lubricant flow is enforced by using a simple algorithm which adjusts the pocket cavitation boundary. With the surface pocket in the center of contact, the Hertzian contact area is divided into two micro-EHL contacts: the inlet micro-EHL contact and the outlet micro-EHL contact. The amount of lubricant trapped inside the pocket determines the overall start-up behavior If the lubricant trapped is less than a critical amount, the two micro-EHL contact would be in start-up condition in serial the lubricant film builds up in the inlet micro-EHL contact area first and then the lubricant film builds up in the outlet micro-EHL contact after the inlet lubricant flow fills the pocket. The start-up time in this case is longer than the start-up time for smooth surface start-up. If the lubricant trapped is more than the critical amount, the two micro-EHL contact would be in start-up condition in parallel: a lubricant film builds up in the inlet micro-EHL contact and at the same time a lubricant film builds up in the outlet micro-EHL contact. The start-up time in this case is much smaller than that of the smooth surface start-up. Compared with the smooth surface start-up condition, because the solid contact vanishes faster, there would be less frictional heat generated in the contact area and thus the surface temperature rise during the start-up process would be much smaller. These effects could prove beneficial in applications with frequent start and stop or oscillating running conditions, in which direct solid to solid contact occurs at the start (restart) of motion.