Topographical Change of Engineering Surface due to Running-in of Rolling Contacts

Abstract

The above quotation indicates the important of running-in phase, which occurs at the beginning of the contact in a mechanical systems. Tribologist identifies that running-in takes place on the first stages of the practical mechanical system operation such as automotive engines, gears, camshaft and followers, and bearings. Kehrwald (1998) expressed the significance of running-in phase by predicting that an optimized running-in procedure has a potency to improve the life time of a mechanical system by 40% and more and to reduce the engine friction without any material modification. The running-in phase is known as a transient phase where many parameters seek their stabilize form. During running-in, the system adjusts to reach a steady-state condition between contact pressure, surface roughness, interface layer, and the establishment of an effective lubricating film at the interface. These adjustments may cover surface conformity, oxide film formation, material transfer, lubricant reaction product, martensitic phase transformation, and subsurface microstructure reorientation (Hsu, et al., 2005). Next, the running-in phase is followed by a steady state phase which is defined as the condition of a given tribo-system in which the average dynamic coefficient of friction, specific wear rate, and other specific parameters have reached and maintained a relatively constant level (Blau, 1989). Due to the complexity of the involved parameters, the discussion of running-in in this book chapter will be focused on the topographical change, contact stress and residual stress of an engineering surface which is caused by rolling contact of a smooth body over a rough surface. Specifically, the attention will be concentrated on the asperity of the rough surface. There are many applications of the rolling contact in mechanical components system, such as in bearing components, etc., therefore, the observation of the running-in of rolling contact becomes an interesting subject. The obvious examples are the contact of the thrust roller bearing and deep groove ball bearing where the running-in occurs on the rings. Its initial