Lubrication mechanism hydrodynamic

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 ... 

The introduction of surface roughness into Che bearing model has but a small effect upon film thickness prediction under cyclic conditions, but mlcro-elasto-hydrodynamic action effectively smooths out the surface ripples and ensures a fluid-film lubrication mechanism. 

Greenberg et al. compared the effects of IF addition in oil under three lubrication regimes hydrodynamics, mixed and limit [44]. They based the lubrication mechanism of IF on a film formation on surfaces and showed that the IF are most effective at mixed Inbrication because all conditions for a good efficiency of IF are combined, hi the hydrodynamic regime, fullerenes do not have interactions with surfaces. In a boundary Inbrication regime, film formed on surfaces is quickly removed, due to contact severity. 

Unlike traditional textbooks of tribology, in this book we regard boundary lubrication as a limit state of hydrodynamic lubrication when film thickness is down to molecular dimension and independent of the velocity of relative motion. The discussions are based on the existing results, some from literatures but mostly from the authors own work. The topics are mainly focused on the mechanical properties of boundary films, including rheology transitions, molecular ordering, and shear responses. Ordered molecule films, such as L-B films and SAM, are discussed, with emphasis on the frictional performance, energy dissipation and the effects from structural features. Boundary films can be modeled either as a confined substance, or an adsorbed/reacted layer on the... 

Wear can result from a number of different processes, such as corrosion, metal-to-metal contact, or abrasion by solid particles. Corrosion wear can start from acidic products of combustion (Kreuz, 1969) mechanical wear from metal-to-metal contact or abrasion is normally prevented by hydrodynamic lubrication with an oil film thick enough to keep moving parts separated. 

By examining Eq. 6.4-1, as pointed out in Example 2.8, we see that at equal entrance and discharge pressures, the pressure profile exhibits a maximum at H = 2Hq/( 1 + 0), or at z/L = Cq(1 + Co), which for Co 2 is two-third of the way down the channel. This result focuses attention on the important difference between parallel plate and non-parallel plate geometries. In the former, equal inlet and outlet pressures imply no pressurization and pure drag flow in the latter it implies the existence of a maximum in pressure profile. Indeed, as we saw in Section 2.11, Example 2.9, this pressurization mechanism forms the foundation of hydrodynamic lubrication. 

J. Tichy, J. Levert, L. Shan, and S. Danyluk, Contact Mechanics and Lubrication Hydrodynamics of Chemical-Mechanical Polishing", to be published in Journal of The Electrochemical Society, 1998... 

Interestingly, this slip behaviour of hard-sphere glasses is different in nature from that found earlier by Meeker et al. in jammed systems of emulsion droplets [60]. There, a non-linear elasto-hydrodynamic lubrication model, appropriate for deformable particles, could quantitatively account for their observations. It therefore appears that, while slip is ubiquitous for yield stress fluids flowing along smooth walls, the mechanism for its occurrence can be highly system dependent. 

Previous studies have indicated that no hydrodynamic lubrication occurs during CMP.28 3la There is always a physical contact between the wafer and the polishing pad asperities. In the following section, we will see that there is enough evidence to prove interactions between a wafer and a pad. The boundary lubrication associated with tribochemical interactions plays a dominant role. In order to understand the mechanisms of boundary lubrication in CMP, the physical, electrochemical, and mechanical processes of interfaces must be considered. The mechanisms can be classified into the following categories based on the surface physical chemistry of materials involved during CMP. 

The mechanisms of particle removal have been studied in the past few years. Reports show that the particles adhere to a surface primarily by van der Waals forces, electrostatic attraction, or capillary action.2 The cleaning is by hydrodynamic lubrication. The thickness of the hydrodynamic fluid layer, as estimated, was around 3.7 pm.1 On the contrary, numerical analysis concluded that the lift force in the hydrodynamic boundary layer of fluid was too small to lift particles off the surface.3 The possible removal force comes likely from the drag force between the brush and the wafer surface. Major... 

It is obvious from scrutiny of the nature and mechanism of fluid film lubrication that in order for the to lubricate the rubbing of one solid surface against another it must separate them. Hydrodynamic calculations will show whether or not a fluid film of the requisite thickness theoretically can exist under the given pressure distribution over the opposing surfaces. We may therefore take as an idealized criterion of fluid film failure a calculated film thickness of zero. The physical consequence implied by this criterion is that the solid surfaces can then come into direct contact. 

If the idealized concept of fluid film failure proposed above is to have any significance in the world of experimental mechanics and engineering, we must find a basis for its validity and utility. The study of fluid film failure in a practical sense then becomes the study of the behavior of the boundary surfaces of the solids and of the intervening fluid lubricant as the thickness of the lubricant film approaches zero. An important aspect is the reliability of the measurement technique for very thin films. We must be careful not to think of fluid film failure as rupture or breakdown by exceeding the intrinsic strength of the lubricant material. Bulk liquid films do not behave in that way. We know by hydrodynamic theory that the pressure a film of fluid is able to... 

In looking at the basic mechanisms of lubricated sliding friction, the major emphasis falls on the adhesive process because a p/ilonj. it is the one most likely to be influenced by the presence of the lubricant at the rubbing interface. The mechanisms to be considered here in particular are those that make their effect felt in thin film or boundary lubrication. The action of macroscopic liquid films, generated hydrodynamically or otherwise, are not included in this treatment because the surfaces are completely separated from each other the meaning of friction in such cases is discussed in Chapter 2. 

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