ABSTRACT
Almost all surfaces found in nature are observed to be rough at the microscopic scale. Contact between two rough surfaces occurs at discrete contact spots. During sliding of two such surfaces, interfacial forces that are responsible for friction and wear are generated at these contact spots. Comprehensive theories of friction and wear can be developed if the size and the spatial distributions of the contact spots are known. The size of contact spots ranges from nanometers to micrometers, making tribology a multiscale phenomena. This chapter develops the framework to include interfacial effects over a whole range of length scales, thus forming a link between nanometer-scale phenomena and macroscopically observable friction and wear. The key is in the size and spatial distributions, which depend not only on the roughness but also on the contact mechanics of surfaces. This chapter reexamines the intrinsic nature of surface roughness as well as reviews and develops techniques to characterize roughness in a way that is suitable to model contact mechanics. Some general relations for the size distributions of contact spots are developed that can form the foundations for theories of friction and wear.
