The Detection of Fracture Transition Point by the Local Self-Affine Fractal.

Abstract

In the field of the fractography, fractal has been applied to investigate fracture mechanism. In this study, a new method detecting the transition point of fracture surface by calculating the local fractal dimension using Wavelet transformation is proposed. The high accurate evaluation is realized by using not the conventional self-similar fractal but anisotropic self-affine fractal "Hurst exponent" that is more suitable for fracture surface as an evaluation parameter. First, validity of our proposed method was verified by using the synthesized profile. Next, by applying our method to the brittle-ductile transition region of Charpy test specimen, the transition point was shown quantitatively. The homogeneity of fracture surface was checked in the case of TiAl creep and creep fatigue test specimen. Moreover, as compared with the conventional Box-Counting method for the self-similar fractal, it was found that our method with using self-affine fractal gave more exact Hurst exponent, and was suitable also for detection of the variation in local fractal dimension.