Pressure Distribution Within EHD Point Contacts Based on Measured Film Thickness

Surface topography significantly influences the behavior of lubricated contacts between highly loaded machine elements. Most oil- or grease- lubricated machine elements such as gears, rolling bearings, cams and traction drives operate in mixed lubrication conditions and the lubricant film thickness is directly related to the main practical performance parameters such as function, wear, contact fatigue and scuffing. For determination wear and especially contact fatigue, the values and distribution of the pressure in rolling contact are required. The theoretical studies usually involve the numerical solution of pressure and film thickness in the contact, using some physical mathematical model built around the Reynolds equation to describe the flow and the theory of elastic deformation of semi-infinite bodies. Such calculations can be extremely time consuming, especially when lubricant films are very thin and/or contact load very high. This study is aimed at obtaining pressure distribution within lubricated contact from measured film thickness. Lubricant film thickness distribution within the whole concentrated contact is evaluated from chromatic interferograms by thin film colorimetric interferometry. Consequently, an elastic deformation is separated from the film thickness, geometry and mutual approach of the surfaces. Calculation of the pressure distribution is based on inverse elasticity theory. EHD lubricated contact with smooth surfaces of solids was first investigated. Calculated pressure, distributions were compared with data obtained from full numerical solution to check the accuracy. The approach was also applied to surfaces with dents and their influence on distribution of pressure in lubricant film.