The discipline of tribology investigates the effects of mechanical forces during sliding, including energy dissipation, wear and chemical reactions. Various models have been developed to describe these phenomena, but it is becoming evident that these apparently disparate models are based on the same fundamental concept; that an external force lowers the energy barrier for the transition from one state of the system to another. When the initial and final states are identical, only energy is dissipated. However, if the final and initial states differ, the model describe wear or tribo- or mechanochemistry. This concept was first developed by Prandtl in 1928 to describe crystal plasticity, and recently used to describe the velocity and temperature dependences in atomic-scale friction in an atomic force microscope (AFM) by the so-called Prandtl-Tomlinson model. Eyring in 1936 using similar concepts to model liquid viscosity. The way in which these models can describe a wide range of tribological and mechanically induced phenomena is discussed, with examples ranging from atomic and macroscale friction, to material degradation and fracture, to mechano- and tribochemistry. The way in which the external force couples into the system introduces different effects. In the case of constant-force sliding, the external potential V(x) is given by V(x) = -Fx, where F is the constant force, and is predominantly used to describe macroscale phenomena. However, if the external force is harmonically coupled, such as in AFM friction, atomic stick-slip, non-monotonic temperature variations of friction, or extremely low friction (superlubricity) can be obtained.<br/>The concept of stress-assisted, thermal activation provides a link between macro-scale tribological phenomena and their atomic and molecular origins.

Stress-assisted thermal activation in tribology: From friction and rheology to wear and tribo/mechanochemistry

255th National Meeting (2018)

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