The Integrated Digital Image Correlation Technique Applied to Fracture Mechanics: An Improvement on Crack Detection and Localization

Digital Image Correlation (DIC) is a well-known experimental technique allowing for the identification of 2D and 3D displacement fields. iDIC (Integrated DIC) is one of its most successful applications: differently from standard DIC, it uses shape functions that are proper of a specific problem, thus allowing for direct solution of inverse problems. Fracture mechanics is one of the fields in which the iDIC technique has been widely used. To this aim, the terms of Williams' series are used as shape functions, thus allowing for the direct identification of K-I, K-II, and sigma(T). However, proper estimation of fracture mechanics parameters requires identifying the crack tip location and its orientation. Usually, these parameters are defined a priori by the user. The authors propose an enhanced approach based on a hierarchical minimization capable of identifying the crack tip location and of estimating the crack axis orientation. The analysis is performed first on synthetic images to ensure the reliability of the algorithms and then on real data acquired during high-cycle fatigue test. To allow for in-process acquisition, an adaptive acquisition system is developed able to modify the sampling rate during the life test based on the damage evolution.