Elastohydrodynamics

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. 

Wedeven, L., Optical Measurements in Elastohydrodynamic Rolling Contacts, Ph.D. thesis, Univ. of London, 1970. 

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. 

Chang, L. "An Efficient and Accurate Formulation of the Surface Deformation Matrix in Elastohydrodynamic Point Contacts, ASME 7. Tribol,Vol.in, 1989, pp. 642-647. 

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. 

Lubricant Film Thickness in Rough Surface, Mixed Elastohydrodynamic Contact, ASME J. Tribol., Vol. 122, 2000, pp. 

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

Hooke, C. J., Surface Roughness Modification in Elastohydrodynamic Line Contacts Operating in the Elastic Piezovis-cous Regime," Proc. Inst. Mech. Eng., PartJ.J. Eng. Tri- [69] fooZ.,Vol.212,1998,pp.l45-162. 

Elastic recovery, 19 744 in olefin fibers, 11 227—228 Elastic scattering, 24 88-89 Elastic springs, in virtual two-way SMA devices, 22 346-347 Elastic waves, 17 422 Elastohydrodynamic (EHD) lubrication regime, 15 211-212 Elastomer-coated dies, in bar soap manufacture, 22 752 Elastomer designations, ASTM, 9 552t Elastomeric fibers, dyeing, 9 204 Elastomeric polycarboranylsiloxanes,... 

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

Wear of fuel system components can occur due to poor elastohydrodynamic or mixed lubrication properties. 

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 ... 

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