Friction and wear

Friction and wear of materials are the main topics of tribology, which is the science and technology of phenomena occurring at the contact interface between solids. Friction is the resistance to the relative movement between two solids in contact. Wear is the volume loss from solid surfaces in contact which occurs as a result of friction. The following functions have to be taken into consideration in order to understand the mechanisms of friction and wear according to these definitions. (a) Environment: vacuum, gases, liquids. (b) Materials: metals, ceramics, polymers. (c) Surfaces: smooth rough, curved, flat, clean, contaminated, lubricated, coated. (d) Types of contact or loading: stationary, oscillating, sliding, rolling, impact. (e) Electronic and atomic interactions: attractive forces, repulsive forces, adhesion, diffusion. (f) Deformation: elastic, elasto-plastic, plastic, local, general. (g) Heat generation and transfer: adsorption, desorption, chemical reaction, evaporation, melting, softening, phase transition. (h) Fracture: ductile, brittle, fatigue, creep, microscopic, macroscopic. (i) Movement of wear particles: transfer, re-transfer, mixturing, indenting, abrasion, removal. (orig.)