2 - Surface topography and surfaces in contact

Abstract

All surfaces are rough, if only at an atomic level. This chapter explains the concepts behind the measurement and description of roughness, and defines the most common measures of roughness based on line and areal profiles. The topography of typical engineering surfaces is reviewed, and the important concept of asperity contact between surfaces is introduced. Deformation of asperities at low loads is elastic, while at higher loads it is plastic: the theoretical basis of the mechanics of elastic and plastic contact is presented, and then applied to the contact of rough surfaces under normal and tangential loads. The extent of plastic flow depends on the value of the plasticity index which is defined and discussed, and the chapter concludes with some comments on the contact mechanics of coated surfaces and the effects of surface energy on elastic contact.