Elastohydrodynamic lubrication in rolling element bearings: Static and dynamic properties

Rolling element bearings are widely used in rotating machines such as jet engines, pumps and motors. The lubrication of these bearings is essential for their successful operation in machinery. Elastohydrodynamic lubrication is the type of lubrication regime that takes place in the contact areas between the rolling element and the bearing races. The elastohydrodynamic analysis offers the characteristics required to design and understand the operation of the rolling element bearings.;The work of this dissertation focuses on the static and dynamic properties of rolling element bearing contacts. The static properties are: contact pressure distribution, film thickness profile, temperature distribution and subsurface stresses. The dynamic property is mainly the contact stiffness. These properties are governed by the elastohydrodynamic lubrication which is a multi-physics problem that involves two strongly-coupled physical domains: the fluid domain and the structural domain. The thermal distribution is a key factor that cannot be neglected. The cornerstone of a successful elastohydrodynamic lubrication solution is the direct coupling between fluid governing equations and elasticity equations along with the energy equation.;The presented work offers a finite element solution for the coupled elastohydrodynamic lubrication problem and the energy equation. The solution does not require the user's guidance for convergence which is needed for the available numerical methods. Models for the lubricant density and viscosity are included in the fluid model to capture their pressure and temperature dependency. The fluid equations become nonlinear which adds some challenge to the numerical problem. The work addresses three levels for the structural model: a one dimensional model for the line contact, a two dimensional model for the point contact, and a full solid modeling of the contact bodies for the line contact. The different levels provide an understanding of the effect of the contact bodies elasticity on the behavior of the elastohydrodynamic lubrication. For each of the three elastohydrodynamic model levels, the stiffness properties are calculated based on the flexibility of the solid structure and of the fluid film.;For the full solid model, the work shows that the half space assumption over predicts the stiffness of the contact. Taking the actual geometry and profile into account gave lower contact stiffness by about 5%. The subsurface stresses magnitudes for the full line contact model are similar in magnitude to the line contact case but closer to the surface by about 50%. For the modeling of a hardened roller surface, this work shows that the peak pressure increases by about 55% for the studied cases. Tensile stress are generated in the subsurface region which can help in opening any microcracks. The shear stress for the hardened surface increased about 40% and approached the surface by about 15% more. The life of the defected hardened surface roller was shown to be based on the thickness of the hardened layer as well as the hardness level of the layer. The work provides an analysis tool for the mechanical engineer to better understand and optimize the rolling element bearing operation.