On an accurate and automated location of fatigue crack tip by analysing the displacement fields measured with digital image correlation

This paper presents two algorithms for locating the tip of growing fatigue cracks by analysing Digital Image Correlation (DIC) data. This work aims to develop algorithms that are accurate, mathematically simple, easy to implement, and computationally efficient for this purpose. In addition, the goal is to simplify experimental setups and avoid invasive techniques, thereby integrating all measurements into the DIC analysis. The algorithms are implemented by analysing the crack tip displacement fields measured by DIC, establishing the discontinuity along the crack path during fatigue propagation as the basis for estimating the accurate crack tip location. The algorithms were validated through two representative cases: a straight-growing fatigue crack in a Compact Tension specimen made of commercially pure Titanium, and an inclined-growing fatigue crack in a Double Cantilever Beam specimen made of 2024-T3 aluminium alloy. A good level of agreement has been achieved between the results obtained with the implemented algorithms and those from an alternative method, with relative deviations of approximately 2 %.