Advanced modeling of mixed lubrication and its mechanical and biomedical applications

Mixed lubrication is one of the most common types of lubrication found in a wide range of systems, from machine components of drivetrains and transmissions to artificial knee and hip prostheses. The lubricant film in mixed lubrication can be extremely thin, in the same order of magnitude as that of surface roughness, or even thinner, forcing a part of the interactive surfaces into direct contact. Surface topography and material are among the important aspects that determine lubrication pressure distribution, surface deformation, and subsurface stress. Therefore, the study of mixed lubrication must consider the effects of material and surface topographic features. In-depth exploration of mixed lubrication is a key step towards developing methods for friction reduction and wear control. One of the efficient and cost-effective ways to study mixed lubrication is through numerical simulation. The primary challenge is the demand for a large computation power and data storage space. The development of advanced analysis models thus becomes vital to the success of the numerical simulation of mixed lubrication.;This research is focused on the development of mixed lubrication models considering both topographic and material complications, the exploration of the nature of mixed lubrication by means of numerical analyses, and applications of these models in tribological and biomedical designs. The following problems are investigated. Virtual surface texturing has been advanced via refinement of a mixed lubrication model that enables the simulation of surface textures in elastohydrodynamic lubrication (EHL). The effects of micro-scale textures on lubrication enhancement are examined for various texture distribution patterns and bottom shapes together with relative motion design. A line-contact mixed elastohydrodynamic lubrication (L-EHL) model involving three-dimensional (3D) surface topography has been developed for simulating the interaction of cylindrical elements with engineered surfaces. A more complete mixed lubrication model, 3D plasto-elastohydrodynamic lubrication (3D PEHL) model, has been developed by taking into account plastic deformation and material work-hardening. The effect of surface/subsurface plastic deformation on lubricant film thickness, surface pressure distribution, and subsurface stress field has been investigated. The interface of components in an artificial knee replacement involves mixed lubrication, which may be experimentally explored with a Wheel-on-Flat simulator. The mixed lubrication model has been implemented to simulate the interaction between a cobalt-chromium wheel and an ultra high molecular weight polyethylene (UHMWPE) flat. Surface wear of the UHMWPE flat has been predicted with the developed mixed lubrication analysis approach.