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The concept of fractals was used to analyze fracture surface profiles to determine whether fracture surfaces are fractal in nature, and whether the fractal character can be related to either the mechanical properties or the microstructure of the specimens. Sections taken through the fracture surface of fracture toughness specimens were metallographically prepared and photographed, and the fracture profiles were digitized. Simple computer programs which used different techniques to measure the length of the fracture profiles with differing degrees of precision were used to analyze the profiles by generating a fractal plot of apparent profile length versus the measurement step size. The accuracy of the computer programs was verified by examining artificially generated profiles which had a known fractal character. The analyses indicated that fracture surface profiles are indeed fractal, at least over a limited range of detail. However, it was not possible to match the fractal dimension of the fracture profiles to either the mechanical properties of the metals or to their microstructures. In addition, different profiles taken from the same specimen had different fractal dimensions. Discontinuities in the fractal plot could not be related to the microstructural features. Therefore, although fracture surface profiles are fractal in nature, it appears that this information is not useful in understanding the relationship between the microstructure and the mechanical properties.
fractal, quantitative fractography, fracture surface, roughness, fractography
Oak Ridge National Laboratory, Oak Ridge, TN