SURFACE ROUGHNESS EFFECTS IN MIXED RHEOLOGICAL THERMO-EHL ROLLING/SLIDING LINE CONTACTS

Abstract

Elastohydrodynamic lubrication of rolling/sliding line contacts is of great relevance in the successful operation of the mechanical components such as gears, roller element bearings, cams etc. which form a vital part of most of the machines. The success of the lubrication system depends upon the existence of a fluid film which has a thickness of the order of 1 gm or even less. Therefore, it is important to be able to predict the fluid film thickness along with the other associated parameters such as pressure distribution, coefficient of friction etc, under the given set of operating conditions at the design stage. In order to meet the growing demand of industry for highly advanced technologies, the operating loads are increasing, the fluid films are becoming thinner and special purpose lubricants are being employed. Moreover, due to increasing competition in the global market, the emphasis is on lower costs and longer lives of the components. In view of these facts, it is necessary to develop a better understanding of as well as to update and simplify the existing methods for analyzing the problems of elastohydrodynamic lubrication. Due to the aforesaid reasons, the focus of attention has shifted to more realistic and complex situations involving the effects of temperature rise on fluid properties, non-Newtonian behaviour of lubricant, surface roughness and dynamic loading. The analyses based on Newtonian fluid model, in general, fail to explain the experimentally measured traction coefficients for various slide to roll ratios. Therefore, in order to obtain a fundamental understanding of lubrication performance and failure in various triboelements, such as rolling element bearings and gears, it is essential to incorporate the effect of non-Newtonian behaviour of fluid in the numerical scheme. Surface roughness is found to play a significant role for the mechanical components operating under elastohydrodynamic and mixed lubrication conditions