Scale effects in dry and wet friction, wear, and interface temperature

Scale effects in tribology at the macroscale to nanoscale are considered. The coefficient of dry friction depends on the real area of contact and the shear strength due to adhesion and two- and three-body deformation. The real area of contact depends on the surface topography and elastic modulus for elastic contact, and on the hardness for plastic contact. The surface topography is scale dependent, on the basis of a fractal model or an empirical rule. The hardness is scale dependent on the basis of the strain gradient plasticity. The adhesional shear strength is scale dependent on the basis of a dislocation-assisted sliding model. The two-body deformation component of the coefficient of friction is scale dependent due to the scale dependence of the average asperity slope. The real area of three-body contact is scale dependent due to the scale dependence of the probability for a particle to be trapped at the interface and shear strength. In the presence of a liquid film the measured value of the coefficient of friction is different from the coefficient of dry friction due to the meniscus contribution. The meniscus force is scale dependent, since it depends on the number of contacts and summit radius of the asperities, which are scale dependent, on the basis of the surface topography. The scale dependence of other parameters of tribological importance, such as the wear coefficient, which depends on the scale dependent hardness, and the interface temperature rise, which depends on the scale dependent mean contact size, is also considered.