Abstract: To address the existing problems of fractal theory, a piecewise calculation model was proposed. This new model was calculated by different functions with the corresponding parameters set by the wavelength. The fractal detail and deformation process of asperity were considered in this model. The contact deformation process of rough surface was studied and the relationship between real contact area and load was given. The analysis results showed that contact deformation process of rough surface is a transition from plastic to elastic contact model, where elastic deformation and plastic deformation model alternately take place. The top radius of curvature of the asperity is a fixed value which is independent of the deformation under a certain scale. When the fractal dimension is close to 1, the rough surface is dominated by the plastic deformation, and the surface contact property is only affected by the material. An optimal value of fractal dimension is existed when the rough surface contact property is the best.

Key words: fractal; rough surface; asperity; contact