Elastohydrodynamic lubrication in rolling and sliding contacts
Abstract
Elastohydrodynamic (EHD) lubrication is a form of fluid-film lubrication where the elastic deformation of the lubricated machine element in the contact region is significant. Under EHD lubrication, the pressure and temperature induced by the hydrodynamic motion within the fluid film cause a cyclic-stressed condition which results in severe fatigue and reliability problems. Therefore, a better understanding of the state of stress could greatly improve the design of machine elements operating under EHD lubrication. The objective of this study was to develop numerical models to analyze elastohydrodynamic lubrication under rolling and sliding conditions. A satisfactory solution of the EHD problem requires the simultaneous solution of the hydrodynamic motion of the lubricant, the elastic deformation of the solids, and the energy transfer within the fluid film. The nonlinear Newton-Raphson method was implemented to obtain the hydrodynamic pressure and the lubricant film thickness in the conjunction region. The control volume finite element method was used to provide the temperature rise within the lubricant film. The developed models were tested for various loads, speeds, slip ratios, and lubricant models. Some of the models developed in this study are: 1. Surface roughness effects on EHD lubrication. A numerical model was developed to incorporate the effect of surface roughness in EHD lubrication. The effects of various loads, surface pattern, and roughness parameter were investigated. 2. Thermal effect on EHD lubrication. A complete solution of the thermal compressible elastohydrodynamic lubrication problem was obtained. The objective was to investigate the load, speed, and slip effect on lubricant temperature, film thickness, and surface traction. 3. Non-Newtonian effect on EHD lubrication. The hydrodynamic motion of the lubricant was solved considering a non-linear rheology fluid model. Numerical solutions were presented for a wide range of load, speed and slip ratios. The results from the EHD lubrication analysis were used to calculate the subsurface stress distributions. The effects of surface pressure and traction on the mechanical subsurface stresses were discussed. In addition, the thermoelastic effect on EHD lubrication due to the heating input from the hydrodynamic motion of the fluid film was investigated. The thermal stresses were calculated and compared to the mechanical stresses. The effects of thermal stresses on the location and magnitude of the maximum shear stress were also presented.
Degree
Ph.D.
Advisors
Sadeghi, Purdue University.
Subject Area
Mechanical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.