Evolution of Surface Topography During Wear Process

Abstract

There is an increasing demand for high power density (power throughput/weight) machines such as wind turbines, gear boxes, electric drive trains, and turbines. This requires design of heavily loaded tribological components such as bearings, gears, CVT etc., for preventing surface failure. Tribology analyzes surface contacts between two bodies which are in relative motion. To separate contacting surfaces lubricant is supplied between contacts which form a film. In lubricated non-conformal concentrated contacts (e.g. gears, bearings, cams etc.), it is always desirable to run the components in elastohydrodynamic regime for longer life and negligible wear. However, what is achieved is mostly boundary and mixed lubrication regimes. This is because it is almost impossible to create a surface with negligible roughness. The reason is manufacturing and machining processes by which solid components are produced. During the material processing, texture form on the surface of the components which is in form of roughness, waviness and form. The cavities, voids, inclusions are also induced on the surface during heat treatment. When components are subjected to rolling/sliding motion, these defects (roughness and inclusions) act as stress raisers which is responsible for the crack initiation and crack propagation and ultimately material fails due to material degradations in form of tiny particles (e.g. micro pitting) or in form of spall (macro pitting). Recently, the research has been focused on effect of surface topography on the life of tribological components. This chapter demonstrates the determination of important surface topography parameters by using statistical and fractal methods. Later on, evolution of topography parameters during the wear process is explored in detail and it will be shown that surface topography parameters significantly vary during wear.