Entropy and Dissipative Processes of Friction and Wear

Friction and wear, often treated as unrelated, distinct phenomena, are manifestations of the same dissipative physical processes occurring at sliding interfaces. Friction force dissipates power and generates entropy. Wear irreversibly changes a material structure, often with loss of material. Associated with both friction and wear is production of irreversible entropy by interfacial dissipative processes. This article relates friction and wear through the irreversible dissipative processes occurring at sliding interfaces and the concomitant entropy produced. First, friction, wear and laws of thermodynamics are reviewed. Dissipative processes common to sliding interfaces and associated with types of friction and wear are identified and discussed. Finally, friction and wear are related to these processes, and to each other, via the Degradation-Entropy Generation theorem, which formulates wear in terms of the irreversible entropy produced, and a combination of the first and second laws of thermodynamics that relates work of friction to the irreversible entropy of the dissipative processes.