DESCRIBING GROUND SURFACE TEXTURE USING CONTACT PROFILOMETRY AND FRACTAL ANALYSIS

The topographies of ground metallic surfaces with four different hardnesses were studied using contact profilometry, conventional roughness analysis, fractal analysis, and scanning electron microscopy (SEM). The conventional roughness values were found to be proportional to the inverse of the square root of the hardness, minus a constant. Observations in the SEM clearly show that the surfaces are deformed by the passage of the mechanical stylus used for the profilometry. Fractal analysis was effected by estimating the length of digitized profiles by measuring them with different length rulers, and then plotting the log of the relative lengths of the profiles vs. the log of the ruler lengths. From these plots it is seen that these ground surfaces exhibit fractal characteristics over a certain range of scales, i.e. ruler lengths. This range appears to be limited at smaller scales by the measuring methods. From these compass-method fractal plots, in addition, it is possible to determine a roughness threshold, the length below which the surface appears rough, and above which it is smooth. The influence on the plots of different measuring options, i.e. tracing length, point density, and starting point, were studied.