Lubrication elastohydrodynamic

Conformal bearing geometry is associated with the support of large loads by relatively thick lubricant films at relatively low maximum film pressures. Counterformal geometry, on the other hand, is associated with concentrated loading. The Reynolds equation has been solved for 

a is a constant called viscosity pressure coefficient and t)q is the viscosity at ambient pressure. This Bams law tells us that the higher the pressure, the harder it becomes to squeeze the lubricant out of the gap. At the very high pressures of ssl GPa, there may even be a phase transition of the lubricant to a glassy state. 

Both effects allow stable lubrication with surfaces separated by a lubricant layer for contact pressures up to more than 1 GPa. A comprehensive book on this topic is Ref [958]. For reviews, see Refs [959, 960]. 

the dimensionless speed U, the dimensionless material parameter G, and the dimensionless load per unit length Wi are given by 

Pi/l is the normal load per unit length of the cylinders. The reduced radius and reduced Young s modulus are defined as usual as 

Ertel recognized that the pressure drop in the lubricant at the outlet should lead to a reduced deformation of the surfaces and thus to a restriction in the film that results in a pressure spike just before the outlet. A first numerical solution for the pressure profile of a line contact was published by Petrusevich [964], who also calculated the height of the second pressure peak close to the outlet, which then became known as the Petrusevich pressure spike. In 1959, an improved numerical approach was introduced by Dowson and Higginson [965]. It laid the foundation for elastohydro-dynamic lubrication as a distinct field of research. While experimental proof of the existence of a lubrication film and determination of its shape by optical interferometry [966, 968] in highly loaded point contacts was found at around the same time, it took much longer to solve the problem theoretically [969, 970]. Today, computer power and development of efficient algorithms have made computer-based solutions 

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Elastohydrodynamic Lubrication (EHL). Lubrication needs in many machines ate minimized by carrying the load on concentrated contacts in ball and toUet beatings, gear teeth, cams, and some friction drives. With the load concentrated on a small elastically deformed area, these EHL contacts ate commonly characterized by a very thin separating hydrodynamic oil film which supports local stresses that tax the fatigue strength of the strongest steels. 

Du, H. S., "Study on Elastohydrodynamic Lubrication with Fluorescent Technique, Beijing, Ph.D thesis, Tsinghua University, 1999. 

Thin film lubrication (TFL), as the lubrication regime between elastohydrodynamic lubrication (EHL) and boundary lubrication, has been proposed from 1996 [3,4], The lubrication phenomena in such a regime are different from those in elastohydrodynamic lubrication (EHL) in which the film thickness is strongly related to the speed, viscosity of lubricant, etc., and also are different from that in boundary lubrication in which the film thickness is mainly determined by molecular dimension and characteristics of the lubricant molecules. 

In elastohydrodynamic lubrication, the formula of film thickness was given by Hamrock and Dowson [44] as ... 

Hamrock, B. J., and Dowson, D., Isothermal Elastohydrodynamic Lubrication of Point Contact Part I—Theoretical For-... 

As noted before, thin film lubrication (TFL) is a transition lubrication state between the elastohydrodynamic lubrication (EHL) and the boundary lubrication (BL). It is widely accepted that in addition to piezo-viscous effect and solid elastic deformation, EHL is featured with viscous fluid films and it is based upon a continuum mechanism. Boundary lubrication, however, featured with adsorption films, is either due to physisorption or chemisorption, and it is based on surface physical/chemical properties [14]. It will be of great importance to bridge the gap between EHL and BL regarding the work mechanism and study methods, by considering TFL as a specihc lubrication state. In TFL modeling, the microstructure of the fluids and the surface effects are two major factors to be taken into consideration. 

Thin him lubrication is essentially a transition lubrication regime between elastohydrodynamic lubrication and boundary lubrication regimes. Papers devoted to the investigations of this lubrication regime are not enough for engineering needs. In this section, a function to describe the viscosity distribution is proposed in order to attain predictive results and to describe the characteristics of TFL in the viewpoint of engineering. 

Das, N. C., Elastohydrodynamic Lubrication Theory of Line [39] Contacts Couple Stress Fluid Model, Tribal. Trans., Vol. 40, No.2,1997,pp.353-359. 

Yang, P. and Wen, S., A Generalized Reynolds Equation for Non-Newtonian Thermal Elastohydrodynamic Lubrication," ASMEJ. Tribol,MoX.Wl, 1990,pp.631-636. 

Ai, X., "Numerical Analyses of Elastohydrodynamically Lubricated Line and Point Contacts with Rough Surfaces by Using Semi-System and Multi-Grid Methods, Ph.D. Thesis, Northwestern University, 1993. 

Holmes, M. J. A., "Transient Analysis of the Point Contact Elastohydrodynamic Lubrication Problem Using Coupled Solution Methods," Ph.D. Thesis, Cardiff University, 2002. 

Kaneta, M. and Nishikawa, H., "Experimental Study on [61] Micro-Elastohydrodynamic Lubrication, Proc. Inst. Mech. 

Ehret, R, Felix-Quinonez, A., Lord, J., Jolkin, A., Larsson, R., and Marklund, O., Experimental Analysis of Micro-Elastohydrodynamic Lubrication Conditions, Proceedings [64]... 

D. Dowson and G. R. Higginson, Elastohydrodynamic Lubrication, Pergamon, Oxford,... 

European Community European Commission Environmental. Council (Japan) Environment Canada energy conserving. Engine Fuels Technical Committee (CEC). Elastohydrodynamic (lubrication). 

This application illustrates the fact that friction will often be reduced by the addition of molybdenum disulphide to an oil where the geometry is such that the particles can enter the oil film and be loaded against the bearing surfaces. This is the case when boundary lubrication is occurring, and frequently when elastohydrodynamic lubrication is taking place. It can also arise where hydrodynamic lubrication is marginal, and it is often in such cases that frictional heating problems and premature failures occur. 

Fig. 18 Pairwise elastohydrodynamic lubrication interactions between two neighboring particles i and j...

The downside is that these base oils have lower values of pressure viscosity coefficients and hence under both hydrodynamic and elastohydrodynamic lubrication conditions, the films formed in contacts will be thinner than that for an iso-viscous, higher sulphur basestock. 

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