Generalized Newtonian viscosity functions for hydrodynamic lubrication

- Measurements which penetrate far into the shear-thinning regime.
- Review of viscosity functions and their properties.
- Review of superposition.
- New viscosity function for multiple transitions which resolves issues with previous functions.

Among some of the generalized Newtonian viscosity functions used in hydrodynamic lubrication, the Cross and Ellis equations have a transition from the first Newtonian plateau to the power-law regime that is much broader than is typical of polymer-thickened oils. The Dobson method employs the Cross equation to extract the second Newtonian viscosity for a polymer-thickened oil from ambient pressure viscometry. This method will always produce a second Newtonian viscosity for a polymer thickened oil, even if none is present in the data. Shear-thinning measured at elevated pressure removes this issue.An improved viscosity function is offered which describes the shear-dependence of the polymer and of the base oil without the artifacts associated with a sum of individual viscosity equations.