A Surface Layer Model for Thin Film Lubrication

A rheological model has been developed which can be applied to thin film lubrication. It is known that great differences are seen between behavior in thin (molecular scale) films and in bulk (macroscopic) rheological measurements. There appear to be layers near the surface in which viscosity is increased by many orders of magnitude. The model contains three material property parameters, i.e., the conventional viscosity, the thickness of the surface layer, and a surface layer viscosity. A modified Reynolds equation is developed. Behavior of correction factors to Reynolds' equation and to the shear stress are shown. Results are computed for a one-dimensional converging wedge contact. The effect of increasing the layer thickness parameter is to increase the load and reduce the friction coefficient. Increasing the surface layer vicosity also tends to increase the load and reduce the friction coefficient.