Rough surface lubrication

As the statistical models for rough surface lubrication and contact are established, a mixed lubrication model can be thus constructed in the following procedure. 

To examine the effects of height distribution on mixed lubrication, rough surfaces with the same exponential autocorrelation function but different combinations of skewness and kurtosis have been generated, following the procedure described in the previous section. Simulations were performed for the point contact problem with geometric parameters of... 

Fig. 30, while level-off phenomenon can be observed from the simulation result given in Fig. 33 for the rough surface in mixed lubrication. It is unclear at the present whether the downward turn shown in Fig. 30 is a manifest of real physical process, or a false phenomenon due to numerical inaccuracy. 

Christensen, H., "Stochastic Models for Hydrodynamic Lubrication of Rough Surfaces, Proc. Inst. Mech. Eng., PartJ J. Eng. Tribol.,Wo. 184,1969-70,p. 1013. 

Qiu, L. and Cheng, H. S., Temperature Rise Simulation of Three-Dimensional Rough Surface in Mixed Lubricated Contact, ASMS/. Tribol,Vol. 120,No.2,1998,pp. 310-318. 

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. 

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

When chemical reactions are involved in a process, it is important to know the reaction temperature. In the model described here, reactions at a point on the wafer surface are assumed to be driven by temperature excursions due to contact by passing pad asperities. This is known as flash heating. In systems in which there is dry sliding contact between two rough surfaces, it is known that flash temperatures at asperity contacts can be much higher than the average temperatures of the workpieces involved. In CMP, however, the contact is lubricated and cooled by the slurry, and this needs to be taken into account. In the case of polishing on a rotary tool, it is possible to derive a simple estimate of the mean reaction temperature, and it is this that we use in the chemical part of the two-step model. 

Problem 5-10. Drag Due to a Rough Surface. Consider a rough but lubricated surface moving over a smooth surface with velocity Uas indicated in the figure. The rough surface is located at h(y) above the smooth surface as given by... 

If the fluid film separating two metallic bounding surfaces is an electrical insulator, then loss of insulating behavior and appearance of conductance can be interpreted as contact between these surfaces. This is the premise behind the electrical conductance method of detecting lubricant film failure. A practical limit on the applicability of this premise is electrical breakdown of the fluid as thinning of the film concentrates the field intensity. Another complication arises from the fact that for the structured surfaces of every day experience first contact is at the highest asperities rough surfaces may therefore come into initial contact sooner than indicated by the overall trend of the resistance measurements. 

The surface friction is represented by the coefficient of friction, which, in turn, represents the cumulative effects of surface coating, surface fini.sh and surface roughness, surface hardness of both tooling and workpiece, as well as lubricant at the interface [38, 57]. 

Such lamellar structures are even able to prevent contact between highly loaded stationary surfaces. In the direction of motion, the lamellae easily shear over each other resulting in low friction. While larger particles perform best on relatively rough surfaces at lower speeds, finer particles perform best on relatively smoother surfaces and at higher speeds. A comparison of various solid lubricants with respect to their coefficients of friction is shown in Figure 19.2 [4]. 

The quantized friction would be a direct result of the multiple discrete values of the adhesion-controlled contribution to the total friction, and could be a common feature for fluids able to form thin film-layered structures. The results described by Smith et al. could account for discontinuities in friction across thin films as a function of the number of layers, particularly under boundary lubrication regimes with varying liquid film thickness across the contact zone between rough surfaces. 

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