Mixed lubrication regime

Due to lack of deterministic solutions of mixed lubrication in the literatures, it is difficult to conduct a direct result comparison in the mixed lubrication regime. Considering the fact that at the ultra-low speed mixed lubrication would transit to the boundary lubrication or lubricated contact... 

Caravia, L., Dowson, D., Fisher, J., Corkhill, P.H., and Tighe, B.J. Friction of hydrogel and polyurethane elastic layers when sliding against each other under a mixed lubrication regime. Wear 181-183, 236-240,1995. 

At higher normal force, or at lower lubricant viscosity and velocity, the mixed lubrication regime applies. The thickness of the liquid film, in this case, is comparable to the average surface roughness some asperities can therefore touch one another. 

The effect of polymer brushes in different lubrication regimes is seen in Fig. 4a and b, in which the Stribeck curves obtained from pin-on-disk and MTM measurements are plotted, respectively. The coefficient of friction is plotted against speed multiplied by viscosity for all HEPES-glycerol mixtures both in the presence and the absence of the polymer. As expected, the effect of polymer in reducing the friction is predominantly seen in the boundary-lubrication regime. The effect of polymer on the friction is also extended to the mixed-lubrication regime... 

Smeeth, M., Spikes, H.A. The influence of slide/roll ratio on the him thickness of an EHD contact operating within the mixed lubrication regime. In Proceedings of the 22nd Leeds-Lyon Symposium on Tribology, pp 695-703 (1996)... 

The importance of the lubrication r ime on wear volume was first demonstrated by Chan al (1999). The volumetric wear was shown to correlate fairly well with the X ratio. An increase in the X ratio led to an improvement in the lubrication regime and hence a significant reduction in the wear volume. However, even for a given X ratio, particularly in the mixed lubrication regime, there is usually a large scatter in the wear rates, highlighting the cranplexity of the lubrication and wear medianisms involved. 

The same boundary and mixed lubrication regimes are found in small diameter hard-on-hard metallic implants [10,11,12]. However, beyond a certain diameter, or below a certain clearance, the severity of mixed lubrication diminishes, as hydrodynamic action becomes increasingly significant [1], The severity of surface interaction and wear can thus be controlled through careful design and manufacture to optimise fluid film lubrication effects. 

Paper XV (ii) Calculation of EHL Contacts in Mixed Lubrication Regime... 

This simple surface feature enables insight to some important effects within mixed lubrication regime. After these results three different real surface topographies are compared with each other. Finally the friction calculation will be explained and two Stribeck curves are presented. 

As it will be explained in section 2.3 the mixed lubrication regime needs the solution of the dry contact problem. (Meaning of symbols see [8])... 

The first simulation was done for the dry contact situation as a kind of "worst case regarding the mixed lubrication regime. 

This section describes the calculation of the friction force within the mixed lubrication regime. This is fluid friction due to shear stresses within the... 

The mixed film lubrication model, being more efficient in modelling the effect of surface roughness on the lubricant film shear stresses, gives closer results to the experimental values, as explained above. These results also demonstrate how inqmrtant surface roughness is for the evaluation of the friction coefficient in mixed lubrication regime. 

Such models offer the possibility of predicting piston assembly performance variation with running time and their development should continue. They are currently limited by over-reliance on empirical wear data from laboratory tribometers, interpretation of such data in the mixed lubrication regime and the inability to predict at the microscopic scale, for roughness as well as profile change. 

The evolutions quahtatively shown in Fig.l are based on results obtained for journal bearings, as reported for instance in [4]. Under mixed lubrication regime, for a given value of SP, an increase in load or viscosity as well as a decrease in roughness or hardness tends to decrease f (constant-speed curves) an increase in speed tends to decrease f (constant-load curves). The differences tend to vanish at high values of SP (fiill fluid conditions), at least for journal bearings. Under these conditions, f varies almost linearly if an opportune SP function is chosen. 

A < 0.1 - 1 boundary lubrication regime 0.1-l 2 - 5 full fluid lubrication regime. 

Reply bv the Author Professor Spencer raises an important question. The concept of the Lambda Ration is useful the difficulty lies in its evaluation and application. Since many, hard-on-hard total replacement joints appear to operate in the mixed lubrication regime, both the wear and the friction of such components will depend strongly upon the sharing of the applied load between asperity contact and fluid-film action. Both friction and wear can vary by some two orders of magnitude in the transition from full boundary to fluid film conditions. Furthermore, this transition can be achieved with relatively small changes in operating conditions, as demonstrated by the results shown in the present paper. The Lambda Ratio reflects the... 

Paper XV (ii) Calculation of EHL Contacts in Mixed Lubrication Regime by Dr A C Redlich, Dr D Bartel and Professor L Deters. (Otto-von-... 

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