Novel Self-Adapting Microscale Surface Textures For Hydrodynamic Lubrication

Abstract

The tribological performance of a lubricated surface depends largely on the ability of the surface to maintain a sufficient film thickness under high loads. One way of improving the performance is to modify the surface by inducing changes in the geometry of the surface. This work deals with modeling, creating and testing novel adaptive microscale surface geometries to improve the tribological performance in terms of load carrying capacity. Numerical methods are used to model and simulate the performance of these surfaces. Coupled mechanisms involving elasticity theory and the Reynolds equation were solved for the values of pressure and load acting on the surface. Parametric studies were also performed by varying the input conditions and variables involved. The results were nondimensionalized by using a standard normalization scheme throughout the work to make them easy to compare and deduce the trends. Efforts were made to optimize the geometry of the surface to improve the performance in terms of increased load carrying capacity. Numerical results show that the adapting surfaces are able to increase the effective stiffness of the hydrodynamic film in comparison to conventional textured surfaces. It was theoretically also shown that adapting microscale structures perform better in terms of load carrying capacity for the same amount of film thickness. This is due to the increase in the fluid film stiffness of the adapting or smart surfaces which change their geometric profile according to the applied load. The proposed self-adapting surfaces were fabricated using microfabrication techniques and a test rig to characterize the surfaces was designed and built. The self adapting or smart surfaces were made of Polydimethylsiloxane (PDMS) which is a polymer of silicon. PDMS was chosen for its ease of fabrication and design. PDMS has also the property of optical transparency which helps in viewing the surface behavior when in contact through a microscope. The test rig consists of a load cell to measure the amount of load acting on the surface due to the pressure exerted by the fluid. A variable- speed motor is also part of the rig which can be used to vary the velocities to simulate the real time conditions experimentally. The film thickness too can be controlled accurately at the microscale level with the help of micrometer stages. A microscope was planned to be used to view the whole process and observe phenomenon like cavitation for the better understanding of the surface behavior. Although the test rig was built, due to paucity of time the experimental measurements could not be conducted.