Image Processing Algorithm for Real-Time Crack Inspection in Hole Expansion Test

This paper mainly focuses on development of the smart crack inspection algorithm facilitating the through-thickness crack during the hole expansion test, which makes it possible to calculate the hole expansion ratio, automatically, with the image processing technique. The proposed crack inspection algorithm consists of six steps such as binarization, blob detection, background deletion, ROI selection, image linearization, and crack identification using the C# language. This algorithm is able to capture the various types of the through-thickness and double cracks irrespective of the reflectance and the initial thickness of the applied sheet materials. In addition, it is possible to keep trace of the in-plane crack and its propagation during the HER test.