Simulation of journal bearing friction in severe mixed lubrication – Validation and effect of surface smoothing due to running-in

• Numerical and experimental study of journal bearing friction.
• Stribeck tests are carried out on a journal bearing test-rig.
• Results from mixed elasto-hydrodynamic simulation method match measurement results.
• Simulation model considers non-Newtonian and piezo-viscous behavior of the lubricant.
• Surface parameters for the contact model are derived from surface scans.
• The effect of surface smoothing on journal bearing friction is discussed.

This paper focuses on the friction behavior of journal bearings operating from hydrodynamic to mixed lubrication regime where severe metal–metal contact occurs. Therefore, friction tests with two different static loads are carried out on the journal bearing test-rig from KS Gleitlager. The test results in the form of Stribeck curves provide a solid base to proof the isothermal elastohydrodynamic simulation approach. The simulation approach solves the averaged Reynolds equation introduced by Patir and Cheng and considers metal–metal contact by using the Greenwood and Tripp contact model. All necessary surface parameters are derived from surface scans. No less essential in this approach are the experimentally identified lubricant properties under high pressure and high shear rate.The calculated friction torque matches the measurement results within the measurement uncertainty for a wide range of operation conditions. With the validated simulation approach the influence of surface smoothing due to metal–metal contact is discussed. Additionally, the limits of a constant boundary coefficient are identified and the effects of flow factors are presented.