Effects of non-Newtonian rheology on the line contact elastohydrodynamic lubrication problem.

The Bair and Winer, Gecim and Winer, Circular and Cardiff limiting shear stress models are compared and contrasted under different load, viscosity, limiting shear stress, surface velocities, Young's modulus, relative radius of curvature and temperature. Isothermal comparisons show that limiting shear stress rheology reduces the pressure gradients in the centre of the contact. Also a localised increase in film thickness in the inlet and a reduction near the exit of the contact occur. The bulk oil temperature significantly influences the limiting shear stress features developed. As a result a full thermal approach was adopted that includes the heat generated, by slip, at the fluid-surface interface. Regions where limiting shear stress and temperature effects dominate are identified under optical interferometry operating conditions. The heat generated during contact was included in the thermal approach. Sinusoidal roughness features promoted contact and the temperature responses were compared using different coefficients of friction. Contact develops higher temperatures than those generated in full film regions, with much greater temperature rises for higher coefficients of friction. Thermal and isothermal gear meshes are simulated using equivalent roller and involute geometries with rough and smooth surfaces. Roughness data taken from gear teeth are linked to the numerical involute used in the simulation, allowing roughness features to be used in the correct part of the gear mesh. Smooth and rough surface results are obtained for three different meshes. 'Running in' was investigated by measuring the amount of surface modification and contact developed between two rotating disks using 'in situ' Talysurf profiles and contact resistance measurements respectively. 'Running in' occurred quickly, with temperature effects reducing the films prolonging the contact period. Comparisons using the software developed incorporating actual roughness profiles, bulk disk and bulk oil temperatures, gave good agreement between the numerical and experimental approaches