Aspects of flow and viscoelasticity in a model elastohydrodynamically lubricated contact

Abstract

In order to extend the service life of rolling bearings and other heavily loaded lubricated contacts, the need of lubricant film thickness control significantly increases under more extreme conditions of mechanical and thermal loading and with reduced lubricant supply. To ensure maximum service life, all lubricated contacts should be designed such that under all circumstances a sufficiently large protective layer of lubricant is present to prevent direct contact between the moving parts. Pressures in the order of several gigapascals can be encountered in the contact zone between the moving parts. The field of Elasto-Hydrodynamic Lubrication (EHL) studies cases for which the elastic deformation of (one of) the solids is of the same order of magnitude, or larger, than the film thickness of the lubricant. This thesis focuses on the reseach of highly-loaded circular-shaped EHL contacts, under pure rolling conditions in the low velocity regime. Experimental results for film thicknesses under these conditions show discrepancies with the results from the conventional EHL model. The conventional EHL model assumes that there is always a sufficient supply of lubricant to the contact zone. Extensions of this model for the situation of mixed lubrication (i.e. when one or more parts of the contact do not have a protective lubricant layer present) are not based on first principles and their results depend on the employed computational grid density. The purpose of the present study is to gain more knowledge about how the flow of lubricant around the contact influences the ability to form an enduring lubricant film in the contact zone. A second objective is the development of a model for mixed lubrication from first principles regarding the physics of contact and flow. The model should open a way to better predict EHL contacts in bearings operating in the extreme thin film regime. The approach taken in this research is threefold and involves experimental, analytical and numerical aspects.