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Kinetics and dynamics of frictional stick-slip in mesoscopic boundary lubrication
Authors:O.M. Braun  Erio Tosatti
Affiliation:1. Institute of Physics, National Academy of Sciences of Ukraine , 46 Science Avenue, 03028 Kiev, Ukraine obraun.gm@gmail.com;3. International School for Advanced Studies (SISSA) , Via Beirut 2-4, I-34014 Trieste, Italy;4. CNR-INFM Democritos National Simulation Center , Via Beirut 2-4, I-34014 Trieste, Italy;5. International Centre for Theoretical Physics (ICTP) , P.O. Box 586, I-34014 Trieste, Italy
Abstract:The kinetics and dynamics of frictional stick-slip motion of a slider of size extending from mesoscopic upward is analyzed within the framework of a multi-contact, earthquake-like model. The microscopic contacts are characterized by a distribution of static thresholds for individual breaking. The condition for an overall elastic instability leading to stick-slip sliding are derived and details of the slip motion are studied theoretically. The crucial model parameters emerging from this analysis include the delay time for each micro-contact to reform after breaking, the strength of elastic interaction between the contacts, the elasticity of contacts and of the slider, and the distribution of static thresholds for their breaking. The dynamics is also studied with the help of a scaling procedure. As a prototype application, we adopt parameters appropriate to describe recent surface force apparatus (SFA) boundary lubrication experiments. Despite suggestions of extremely large lubricant viscosities, the experimental data are shown to be fully compatible with ordinary, bulk-like viscosity values once the multi-contact aspects are taken into account.
Keywords:boundary lubrication  nanotribology  viscosity  stick-slip
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