Normal stress effects in viscoelastic fluid lubrication

Abstract

Non-Newtonian flow effects are evaluated in a slider-bearing configuration. The material model taken is that of the Coleman—Noll second-order fluid. An explicit result is given for the portion of the bearing load supported by the non-Newtonian normal stresses as well as that portion resulting from the usual lubrication theory (Newtonian effect). Particular attention is given to the non-Newtonian effect of a high-polymer additive applied to a Newtonian base stock. The non-Newtonian effect has a particular dependence on the bearing geometry as well as a dependence on the relaxation time of the addtive and the amount by which the additive increases the viscosity. The strength of the non-Newtonian effect is assessed in realistic conditions of bearing operation. We find that under certain conditions the non-Newtonian effect could provide a significant load-supporting capability. However, with slight changes in the conditions of the bearing operation, the non-Newtonian load support is negligible. These results are interpreted and qualified with respect to the limitations of the second-order theory, which does not include shear thinning effects.