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The skid resistance is one of the most important using performances of road surfaces. Based on rubber friction theories, this work presents a theoretical method by which the contributions of the roughness elements to the rubber friction can be evaluated in different wavelength ranges. The optimum texture for skid resistance was determined by this evaluating principle. The outward appearance with the optimal texture was generated numerically based on the measured textures of the materials which are commonly used for road surface layers. The potential roughness characteristics of such optimal textures were found out. The results shed a light on the question, which textural properties of typical materials are optimal in road surface layers for skid resistance.Skid resistance means the influences of the material composition and the geometrical shape of the road on the traction in conjunction with the vehicle tires. A skid resistance measurement concerns only a single combination of test conditions. A theoretical method offers the possibility to determine the coefficient of friction at arbitrary combinations of conditions by simple texture measuring. In this sense, a single skid resistance measurement is only a sample point in the whole image of the skid resistance behavior, while the theoretical method can reproduce the frictional behavior in the whole image. There are two basic physical models in the. In both models, the rubber friction is studied by a uniform movement of the rubber slider on a rigid base. In the first model (Klüppel and Heinrich, 2000) pure dry contact is considered. To obtain the correct coefficient of friction, a pre-factor is required, but it cannot be determined explicitly. The second model (Persson 2001) gives the coefficient of friction in both wet and dry roads in proper order of magnitude. The second model makes more sense and has been used for this work and expanded. The first model was used for comparison.The extended model was adapted to the conditions of different skid resistance tests and used for the determination of skid resistance. The viscoelastic properties of two tire rubber and the particular experimental conditions, the coefficients of friction of the texture data different surfaces were calculated. The calculated results were compared with the corresponding measurement results. The correlations were not very strong, but for all experiments, the model always gave the correct order of magnitude of the coefficient of friction. Aside from the case of ViaFriction measurement, there was always positive correlation. So this model tendencially describes the friction processes in the skid resistance tests. The weak correlations can be attributed to the lack of data regarding the exact viscoelastic properties of the test rubber, the exact conditions of the experiments and partly on the weak data quality of some dark colored and sharp texture.With the physical model, it is possible to analyze the contributions of the texture elements in different wavelength ranges to skid resistance. In the first principle no wavelength is excluded in the integration interval. The different wavelengths are firstly considered equal. However, the texture spectrum by the frequency-dependent loss modulus and the contact function is weighted differently. As was demonstrated by a calculation example, the texture elements contribute with wavelength less than 0.1 mm for a quarter of the total friction. With increasing wavelength, the contribution first falls. According to the model of Klüppel and Heinrich the contribution drops monotonically. According to Persson's model contribution in the millimeter range rises again. This rise is conditioned by the scale-dependent contact function. In summary, all the texture elements are important, while texture elements with wavelength less than 0.1 mm and with wavelength on the order of about 1 mm are decisive.Based on the analysis of texture data of the examined surfaces, a rule has been found in terms of the texture spectrum. With the help of an algorithm random surfaces generated with given spectra under this Rule numerically. Your skid resistance under the standard conditions was estimated with the extended friction model. The highest skid resistance texture comes from the group scattered grains and sandpaper. It has a maximum roughness of 2.85 mm, a root-mean-square roughness of 0.36 mm and a coefficient of friction of 2.27 under the standard conditions. The estimated equivalent grain size is approximately 150 microns. The highest skid resistance texture that is similar to conventional exposed aggregates concrete and asphalt surfaces has a maximum roughness of 2.31 mm, a root-mean-square roughness of 0.30 mm and a coefficient of friction of 0.54 under the standard conditions.It must be noted that only the average particle size or surface roughness makes no skid resistance. A realization of exactly this texture would be helpful to verify the statement. In the future, one can construct the surfaces with the optimum texture directly with new technology. It must also be noted that the optimization of the texture in terms of skid resistance should not interfere with the other surface properties, such as reflection, noise emissions, rolling resistance and so on. In this work, they were not taken into account. |
