For well-defined contacts with sizes less than hundreds of nanometers, the friction force-displacement curves are characterized by the stick-slip behavior, which are very sensitive to surface atomic structure, lattice mismatch or incommensurability, sliding velocity, surrounding temperature, to name a few. While the stick-slip behavior can be modeled by the one-degree-of-freedom Tomlinson model, it cannot explain the role of lattice structure and interface defects. Molecular simulations, on the other hand, suffer the temporal limitations and thus have difficulties in modeling the dependence on velocity and temperature. In this work, a Peierls-type model is developed which views the sliding process as the initiation and gliding passage of interface dislocations with diffused cores. The dependence of the friction behavior on the contact size is naturally due to the introduction of the dislocation core size. The spatially inhomogeneous nature of rate-limiting processes is successfully determined, from which a quantitative comparison to the thermally activated friction behavior can be made. A number of experiments in literature will be compared.
 Jinhaeng Lee, Yanfei Gao, Allan Bower, Haitao Xu, George Pharr, Journal of the Mechanics and Physics of Solids, 112, 318-333, 2018.
 Zhiwen Gao, Wei Zhang, Yanfei Gao, Modelling and Simulation in Materials Science and Engineering, 31, 2065-2075, 2016.
 Jiangnan Zhang, Jinhaeng Lee, Jun Lou, Yanfei Gao, Extreme Mechanics Letters, 2, 60-64, 2015.
 Yanfei Gao, Journal of the Mechanics and Physics of Solids, 58, 2023-2032, 2010.
Yanfei Gao is a Professor at Department of Materials Science and Engineering, University of Tennessee, USA. He received his BS degree in Engineering Mechanics and a dual BS degree in Computer Science from Tsinghua University in 1999, and PhD from Princeton (advised by Prof. Zhigang Suo) in 2003. After a two-year post-doctoral training at Brown University, he joined the University of Tennessee and Oak Ridge National Laboratory in 2005. His research activities have been focusing on deformation and failure of advanced structural materials such as metallic glasses, superalloys, high entropy alloys, and structural ceramics. He has published more than 120 journal papers, many of which are in Journal of the Mechanics and Physics of Solids and Acta Materialia. His research has been mostly sponsored by the US National Science Foundation and Department of Energy.
Mechanics of Materials; Computational Metallurgy; Contact and Friction; Mechanics of Evolving Micro/Nanostructures