Fractography of crack networks in thin layers

The subject of this article is detection and description of random networks of cracks on a material surface. Thin layers of (Ti,AI)N on a hardmetal (WC-6%Co) substrate were subjected to thermomechanical loads by laser irradiation. Cracks in the coating caused by this load were examined by scanning electron microscopy (SEM). A special method for automatical detection of cracks in SEM images of the surface is based on the application of edge detection and sequential testing of the course of individual cracks. The system of cracks is classified into branches with respect to passing or finishing in knots. To derive the characteristics of the network, a regression model of branches with user-specified maximum of represented curvature is suggested. As an example of the output, the distribution of the local crack direction conditional on the crack length is shown. (C) 2001 Elsevier Science Inc. All rights reserved.