A More Complete Description of the Shear Rheology of High-Temperature, High-Shear Journal Bearing Lubrication

High-pressure viscometers, which have in the past been used mainly to obtain rheological properties for elastohydrodynamics, can be used to obtain flow curves for motor oils that extend much deeper into the shear-thinning regime than conventional high-temperature, high-shear (HTHS) viscometers and the constitutive information obtained should be immensely helpful in journal bearing calculations. A simple infinite journal bearing calculation shows that the effect of pressure on viscosity is at least as important as the effect of shear rate and that shear rate alone is a poor measure of the extent of shear thinning in a bearing under HTHS conditions. Then variability in piezoviscous response should be at least as important as variability in shear thinning. Sufficiently accurate theory exists to possibly design lubricants for both high load capacity and low friction by balancing pressure and shear rate effects.