M.Sc. Tezi Görüntüleme

      Because of the multiscale roughness of most real surfaces, actual contact is confined at the summits of surface protrusions, commonly referred as asperity contacts. Recognizing the effect of the sample size, instrument resolution and experimental filter on the measurement of the statistical parameters used in traditional approaches to quantify the surface topography, fractal geometry was used to characterize rough surfaces in this thesis. Contact analysis of semi-infinite medium with rough surfaces were performed using finite element method in order to investigate the effects of surface roughness, frictional heating and subsurface cracking on the resulting stresses and deformation. In order to achieve this purpose a two-dimensional finite element model of the rigid rough surface characterized by fractal geometry and polynomial sliding over an elastic-plastic medium was developed. The von Misses equivalent stress, equivalent elastic/plastic strain, pressure and temperature occurred in the semi-infinite medium due to simultaneous mechanical and thermo mechanical surface loading were studied. In this study, the effect of friction coefficient, the sliding distance and the indentation depth called interference in the semi-infinite medium on to deformation were investigated. In addition to this, the propagation of horizontal crack under the semi-infinite medium surface was analyzed using mod-I and mod-II stress intensity factors. The effects of the rough surface model including asperity interactions developed by using fractal geometry for modeling rough surfaces on the stress and deformation distributions were discussed comparatively with other models and its validity was investigated. It was shown that the presented distributions obtained for the stresses, strains, pressures and temperatures are more natural than that of others. It was also presented that frictional heating increases the contact area, contact pressure and also stresses.