Multiscale Modeling of Friction Coefficients: A Review from Nanocontacts to Macroscopic Sliding

Friction, being a very ubiquitous form of energy dissipation and material wear in engineering systems, has a range of physical scales, including atomic interactions and bulk mechanical behaviour. Despite the continued use of the classical laws of Coulomb and Amontons in engineering practice, recent research has shown that the behaviour of friction is much more intricate than can be suggested by these linear relationships. The review gives an overall overview of the progress made in multiscale tribology, including macroscopic measurements of friction, surface roughness modelling, dynamics of stick-slip on the nanoscale, energy dissipation processes, and atomistic simulations. Special attention is given to the effects of surface topography, material structure, lubrication state, and environmental conditions on the value of the friction coefficient in various regimes. The critical roles of interfacial adhesion, third-body effects, and multiphysical coupling in regulating the frictional response are also explained. Additionally, we highlight the development of combined multiscale methods and predictive methods, such as machine learning-based parameter inference and experiment-simulation co-modelling. We discuss that friction has become a complicated interfacial phenomenon with statistically emergent behaviour, and its controlled regulation in detail is necessary through a synergistic framework that cuts across scales and disciplines. Such an approach offers a basis for the rational design of friction in future intelligent mechanical systems.