High resolution and real-time measurement of 2D fatigue crack propagation using an advanced digital image correlation

Abstract

This paper developed a real-time and non-destructive 2D fatigue crack propagation tracing method based on an optimized digital image correlation (DIC) approach by introducing an image in-situ processing algorithm and a fatigue crack propagation monitoring algorithm. The in-situ processing algorithm coupled with optimizing the speeded up robust features (SURF) was applied to correct the shifted images during fatigue crack propagation tests, while the fatigue crack propagation monitoring algorithm was developed to detect the true crack tip and measure crack length. By optimizing SURF algorithm, the construction time of feature descriptor for interest point matching was reduced to 0.0066 s, 55 times shorter than the case using traditional SURF. In conjunction with the fatigue crack identification, this enables the real-time measurement of fatigue crack length with the resolution as high as 5.2 μm for a measurement region of 15.85 × 10.57 mm2. Compared to current DIC, the proposed algorithm either enables characterizing the crack tip and crack propagation path, or can be programmed as user-defined subroutine and integrated into commercial DIC software for example MatchID. As a result, the experimental measurements obtained by the proposed approach on the fatigue crack propagation tests of an Aluminium alloy exhibited a good agreement with simulation results based on the extended finite element method (XFEM), indicated its promising industrial prospect.