Normal contact of fractal surfaces—Experimental and numerical investigations

Describing rough surfaces as a fractal over several length scales enables the application of parameters which are independent of the measurement resolution. To generate a fractal surface the measured structure function of a real surface is approximated by three intrinsic parameters: the RMS value of the roughness, the fractal dimension and the transition length between fractal behaviour at high wavenumbers and stationary behaviour at low wavenumbers. A numerical model which allows to describe the elasto-plastic normal contact of isotropic fractal surfaces is tested against experimental data which are obtained from contact tests of several aluminum specimens. The numerical model and the contact tests are described. Furthermore, a review of influencing variables like hardness and geometrical deviations with larger wavelengths than the roughness is given.