Edge loading and running-in wear in dynamically loaded journal bearings

Abstract

This paper focuses on the beginning phase of hydrodynamic journal bearing life time when the first adaption of the contacting surfaces occurs. Generally, this effect is known as running-in.Experimental data from a journal bearing test rig using a low viscosity 0W20 multi-grade automotive lubricant provide the solid basis for the simulative study of the running-in process. From these measurements and a subsequent determination of the surface roughness, parameters for the mixed lubrication contact model are derived. This analysis combined with the experimentally identified lubricant properties under high pressure and high shear rate enables the evaluation of an iterative simulation approach. In this iterative approach the bearing surface geometry is adapted stepwise until a steady state of operation is achieved.Results show worn regions at the edge of the highly loaded bearing shell. This wear is caused by metal–metal contact due to the elastic bending of the shaft. The calculated wear depth at the edge and the expansion of the worn area in axial and circumferential direction matches the measured profile. This agreement indicates that the simple iterative approach using the Greenwood and Tripp contact model and Archard׳s wear equation is suitable to predict the worn surface geometry after the running-in process is completed.Furthermore, the simulation shows that the maximum asperity contact pressure in mixed lubrication decreases with the stepwise adaption of the surface geometry, until only an insignificant metal–metal contact remains. With this adapted surface geometry, the influence of shaft speed, temperature and surface roughness is also discussed.