Evaluation of boundary fractal methods for the characterization of wear particles

Of the many approaches used to characterize the complex nature of wear particle boundaries, the boundary fractal dimension has often been shown to be particularly useful. Accurate calculation of the fractal dimension can, however, be limited by a problem of variation in step length, the difficulties associated with line fitting into the Richardson plot and the fact that the dimension is sensitive to image noise and focusing. In this paper, the performance of three boundary fractal methods; i.e., the exact ‘hand and dividers’, the fractal analysis by estimation-normalized approach, and the fast Hamblin-Stachowiak method; was evaluated on artificial shapes and wear particle images. The most accurate method for calculating the fractal dimension from a particle boundary was selected. The sensitivity of these methods to image noise and focusing was also examined.