Several theories involving rarely analyzed but yet realistic rheological effects have been developed in an effort to find why lubricant film thicknesses in rolling contact, as measured by X rays for rigorous operating conditions, do not obey simple theories well, especially with respect to load effect. The analysis is based on actions in the inlet zone, using the approximate geometry implied for previous simple theories. Effects investigated include a generalized pressure variation of viscosity, a non-Newtonian rheology of Ree-Eyring form, and a time delay in pressure effect on viscosity. Simple formulas are found for the influence of all these factors on lubricant film thickness. The time delay theory is found to provide the best correlation with experimental measurements of film thickness, and it is suggested to offer an attractive field for further research embracing friction effects as well as film thickness.

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