The classification of rough surfce contacts in relation to tribology

Height and wavelength parameters of surface roughness are varied to show that three types of surface contact can exist in relation to tribology. These are (i) predominantly plastic asperity contact with gaps in the contact interface, (ii) the same contact geometry but with predominantly elastic asperity contact and (iii) almost total surface contact under an elastic state of stress (this state approaches the theoretical smooth surface conditions). These contact states are confirmed by rough surface contact techniques of a ball-on-flat geometry. Results from simple boundary-lubricated sliding tests are also presented to show that the frictional and tribological behaviour differs significantly for each of these contact states. The fundamental implications for tribology are discussed in relation to this work.