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

Abstract

Scale effects in tribology at the macroscale to nanoscale are considered. The coefficient ofdry friction depends on the real area of contact and the shear strength due toadhesion and two- and three-body deformation. The real area of contact dependson the surface topography and elastic modulus for elastic contact, and on thehardness for plastic contact. The surface topography is scale dependent, on thebasis of a fractal model or an empirical rule. The hardness is scale dependent onthe basis of the strain gradient plasticity. The adhesional shear strength is scaledependent on the basis of a dislocation-assisted sliding model. The two-bodydeformation component of the coefficient of friction is scale dependent due to the scaledependence of the average asperity slope. The real area of three-body contact is scaledependent due to the scale dependence of the probability for a particle to betrapped at the interface and shear strength. In the presence of a liquid film themeasured value of the coefficient of friction is different from the coefficient of dryfriction 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 scaledependence of other parameters of tribological importance, such as the wear coefficient,which depends on the scale dependent hardness, and the interface temperaturerise, which depends on the scale dependent mean contact size, is also considered.