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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 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.

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For the study of mixed lubrication in dynamically loaded journal bearings, this paper employs a combined experimental and simulative approach. Extensive measurements on a journal bearing test rig with a low-viscosity 0W20 multi-grade lubricant with a strong Non-Newtonian behaviour provide the basis for the investigation of the lubrication conditions in journal bearings. In this paper, temperature effects and the influence of running-in (breaking-in) wear are investigated. To this task, a high dynamic load is applied to the journal bearing under test. To vary the lubrication conditions, only the journal speed is changed. To investigate the lubrication conditions a detailed and validated simulation approach is utilized that takes into account both the piezoviscous effect and the non-Newtonian behaviour of the investigated lubricant as well is able to describe metal-metal contact. With this combined approach the run-in process of the journal bearing under test can be investigated as well as the role of temperature settling effects.