An Approach for Quantitative EHD Friction Prediction Based on Rheological Experiments and Molecular Dynamics Simulations

Lubricated friction is controlled by the contact operating conditions, including temperature, normal load and sliding. In the elastohydrodynamic (EHD) regime, the rheological characteristics of the lubricants are also dependent on these conditions. Under extreme contact conditions (high load, high sliding), a possible friction plateau (limiting shear stress phenomena) can appear, making friction independent of the sliding speed. Since the physical origin of this friction plateau remains unclear, despite many efforts from the tribology community, predicting friction in EHD contact is still challenging. This work introduces an original EHD friction prediction approach built on a completely independent process from the tribological test. It consists of implementing two models a viscosity model based on the rheological experiment and molecular dynamics simulation data combined with a thermal-elastohydrodynamic contact model. Two fluids with different natures are studied squalane and benzyl benzoate. Friction predictions, including friction plateau and thermal effects, are obtained for both fluids and compared with experimental friction measurements, and a quantitative agreement is obtained. In addition, the role of the thermal effects on EHD friction and the origin of the friction plateau are investigated.