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Abstract
In this work the Johnson-Segalman fluid model is employed to investigate the combined effects of elasticity and shear thinning on the load bearing capacity of lubricants under isothermal conditions. A dimensional analysis, using characteristic lubricant properties and realistic bearing operating conditions, yields a simplified set of equations for the stresses and the balance of mass and momentum. A perturbation solution to these equations gives the stresses, velocities and pressure as second order expansions in the powers of Weissenberg number, We.
The results of this study show that for characteristic lubricant relaxation times of few microseconds, lubricant elasticity (including stress overshoots) has negligible influence on the load bearing capacity of short journal bearings. Additionally, the Johnson-Segalman solution reveals that when both elasticity and shear-rate dependence of viscosity are present in a lubricant, the latter phenomenon is of overriding importance and leads to a decrease in the load bearing capacity. Experimental studies conducted by other workers are cited in support of this finding.