The fractal character of processed metal surfaces

The fractal character of lapped and shaped Babbitt alloy surfaces was investigated by using the structure function analysis method, and the fractal parameters D and G of these two typical kinds of engineering surfaces were determined. It is shown that the random lapped surface was fractal and had a bifractal structure within the range of length scale investigated in this paper. Like the traditional roughness parameters of the lapped surface, its fractal parameters in different measuring directions had almost the same value. A periodic shaped surface was also fractal when the length scale was smaller than the mean spacing roughness S-m, but its fractal parameters in the direction orthogonal to the machining direction differed greatly from those parallel to the machining direction just as its traditional roughness parameters did. The scale-independence of fractal parameters D and G was studied by changing the sampling spacing Delta t of the computer system, which corresponds to spatial measuring resolution, and sampling length L during surface profilometry. Experimental results show that the sampling spacing Delta t did not affect D and G values. Sampling length L did not effect D and G values when L much greater than S-m, but too short a sampling length L meant these two fractal parameters changed. The reasons causing this phenomenon are discussed in this paper. (C) 1997 Elsevier Science S.A.