Quantitative Study on the Friction of Different Types of Base Oils Based on Stribeck Curve and Traction Curve Characterization

Oils with low-friction performance are essential to meet the evolving requirements of the modern industry. Except for the viscosity, there is still a lack of a high-pressure rheological parameter that can quantitatively compare the friction performance of base oils. This study investigated the frictional behavior of six types of base oils with identical viscosity at 40 °C—paraffinic mineral oil 500N, naphthenic mineral oil, polyalphaolefin (PAO), oil-soluble polyether, ester oil, and alkyl naphthalene. Stribeck and traction curves were measured. The limiting shear stress (LSS) has been proposed and modeled for the quantitative comparison of the friction behavior of the base oils at high pressures (1.2–1.7 GPa). Results indicate that the PAO exhibits the lowest friction coefficient. Additionally, the LSS of all tested oils has a linear relation with the average contact pressure (R2 > 99%), suggesting that the LSS at different mean contact pressures can be predicted using a linear LSS-pressure fitting model. This work contributes to providing fluid rheological models for the quantitative EHL friction prediction and provides guidance for choosing low-friction base oils for EHL-lubricated rolling/sliding contacts.