Lubrication mechanism elastohydrodynamic

Liquid lubrication mechanism. There are four defined regimes of liquid lubrication hydrodynamic (thickness of lubricant film (h), h > 0.25 pm), elastohydrodynamic (h 0.025 to 2.5 pm), boundary (h 0.0025 pm), and mixed. These regimes are dependent on oil viscosity (Z) and relative velocity (V) and are inversely proportional to the load (L), (ZV/L). Fig. 5.1, known as the Stribeck-Hersey curve, depicts these regimes in terms of friction coefficient versus viscosity, velocity, and load (ZV/L) (Fusaro, 1995). 

Lubrication mechanism How do you expect each of the following regimes to change in going from thickness of lubricating film h to a coefficient of friction, p in the Stribeck-Hersey curve Fig.5.1 There are three defined regimes of liquid lubrication (a) hydrodynamic, h 25 pm, (b) elastohydrodynamic, h = 0.025 to... 

Nascent surface Explain the difference in the concept of liquid lubrication mechanism in (a) hydrodynamic, (b) elastohydrodynamic and (c) boundary lubrication. Which of the following characterize (a), (b), and (c) lubrication regime continuous fluid film, negligible deformation, complete separation of the surfaces, elastic and plastic deformation, no wear takes place, no contact between the sliding surfaces, involving surface topography, physical and chemical adsorption, catalysis and reaction kinetics, and tribochemical film formation ... 

Experimental confirmation of the elastohydrodynamic lubrication theory has been obtained in certain selected systems using electrical capacitance, x-ray transmission, and optical interference techniques to determine film thickness and shape under dynamic conditions. Research is continuing in this area, including studies on micro-EHL or asperity lubrication mechanisms, since surfaces are never perfectly smooth. These studies may lead to a better understanding of not only lubricant film formation in high-contact-stress systems but lubricant film failure as well. 

It is known from recent investigations (2, 3, 4) that the transient elastohydrodynamic film formation and supplemental lubrication mechanism such as micro-elastohydrodynamic lubrication, weeping, blphasic, boosted or boundary lubrication are capable of providing sufficient protection to the articular cartilages in natural joints. On the contrary, there is just a little information on the actual lubricating film formation in total replacement joints. 

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. 

When one considers this mechanism of elastohydrodynamic lubrication, the question may arise, as to why one should ever see the failure of a lubricant. While the answer has yet to be determined definitively, two possible explanations are (1) even at the extremely high pressures involved, the extreme local temperatures that also exist surpass the critical point so that the lubricant is effectively evaporated away or (2) shear forces near points of contact are sufficient to effectively break up the solidified lubricant film, leaving bare spots that can have direct contact, leading to excessive wear and possible seizure. 

Jagatia, M and Jin, Z M, (2001), Elastohydrodynamic lubrication of metal-on-metal hip prostheses under steady-state entraining motion. Proceedings of the Institution of Mechanical Engineers, Part H , Engineering in Medicine, Volume 215, pp 531-541. 

Ville F., Nelias D., Tourlonias G., Flamand L. Sainsot P., "On The Two Disc Machine A Polyvalent and Powerful Tool to Study Fundamental and Industrial Problems Related to Elastohydrodynamic Lubrication ". Tribology series Tribology Research From model experiment to industrial problem A century ol efforts in mechanics, materials science and physico-chemistry , D. Dowson et al. Editeurs. Elsevier, Amsterdam, 2001, Vol. 39, pp.393-402... 

Pemberton, J., Evans, D., and Cameron, A., 1976, A Mechanism of Fluid Replenishment in ElastoHydrodynamic Contacts , WEAR, 37, pp. 184-190. Wolveridge, P.E., Baglin, K.P., Ar-chard, J.F., 1970-1971, The Starved Lubrication of Cylinders in Line Contact, Proc. Inst. Mech. Engrs., 181, pp. 1159-1169. Hamrock, B.J., and Dowson D., 1977, Isothermal Elastohydrodynamic Lubrication of Point Contacts, part IV, Starvation Results, ASME J. Lub. Tech., 99, pp. 15-23. Chevalier, F., Lubrecht, A.A., Cann, P.M.E., Colin, F., Dalmaz, G., 1995, Starvation Phenomena in EHL Point Contacts Influence of the Inlet Flow Distribution , Proceedings of the 22st Leeds-Lyon... 

The first theoretical description of elastohydrodynamic lubrication for the fine contact problem relevant to gears that combined the Reynolds equation. Bams law, and a Hertzian contact mechanics was developed by Ertel [961] and pubhshed 10 years later by Gmbin and Vinogradova [962]. The approach was to assume a Hertzian contact to calculate the pressure in the gap and let the pressure in the lubricant before the entrance increase exponentially to match the Hertzian contact pressure curve. The pressure distribution for such a line contact between parallel cylinders is shown in Figure 9.12. With this approximation, Ertel derived an expression for the average thickness ho of the lubricant film within the gap, which was later refined by Dowson [963] ... 

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