Partition of Charpy fracture surface with digital image processing

The fracture surface of a Charpy specimen contains information that can enrich the outcome of the test which at present is only the total energy absorbed. An automatic digital image processing technique based on the Horowitz and Pavlidis (1976) split-and-merge algorithm is proposed for partitioning Charpy fracture surface into regions with clear physical and mechanical meaning. Initial ductile fracture region, brittle zone and post-cleavage ductile shear region can be identified based on their relative brightness. Various geometrical properties of each region can then be easily calculated. The technique has been tested on a group of 773 broken Charpy samples made of TMCR and ship steels. The percentage of crystallinity calculated with the proposed technique agrees reasonably well with that obtained with visual inspection. Finally the potential of the technique and the ambiguity of the partition criterion based on surface light reflectivity are discussed.