Visualization and measurement of crack extensions in metal brittle fractures

A brittle fracture, which is a kind of metal fractures, accompanies little or no plastic deformations of the metal. The origin of the fracture and the crack extensions are the most important clues to identify the cause of it. Here, fractography is an area of study to analyze fracture mechanisms and/or causes by using electron microscope images. The method to locate the origins was established through it. [1][2] The goal of this study is, in order to expand the above researches, to visualize the crack extensions and to measure each of extension in micron scale. To implement it, firstly, all cleavage steps and river patterns in a SEM image are identified using brightness threshold. Several river patterns can be directly detected, which show the cracks extended along them. In addition, some cleavage steps which presumed to be parts of a river pattern; however, they are fragmented and do not clearly present that the crack outspread along them. Therefore, secondly, those fragmented steps are connected using coherence enhancing diffusion method. performs an anisotropic diffusion process on the image to increase the coherence of the image structures, and non-continuous steps can be connected without being smoothed perpendicular to their dominating directions. Thirdly, each specified extension line, or pseudo river pattern, can be image-measured of its features such as location, orientation and size. It is expected that the proposed methods will enable non-experts to analyze metal fractures accurately in micron scale.