Scale effects in friction using strain gradient plasticity and dislocation-assisted sliding (microslip)

Scale effects in dry friction at macro- to nanoscale are considered. According to the adhesional model of friction, the friction force depends on the real area of contact and the average shear strength of asperity contacts during sliding. The scale dependence of the so-called geometrically necessary dislocations causes enhanced hardness with decreasing scale. In the case of plastic contacts, enhanced hardness results in a decrease in the real area of contact. The average shear strength at the interface is associated with dislocation-assisted sliding (microslip) and increases with decreasing C 9 scale. from geometrical considerations. In cases of single-asperity and multi-asperity elastic or plastic contact, the scale dependence of the real area of contact and shear strength results in scale-dependent friction. Comparisons of the model with experimental data are also presented. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.