Analysis of the Displacement Field Along a Surface Crack with Moiré Interferometry

Structural components may have cracks, and in these components, a crack tip represents an extremely concentrated stress. Obtaining an accurate assessment of the related strain gradient is challenging when using discrete experimental methods. An efficient alternative is the use of optical techniques, which do not require physical contact. These techniques provide continuous information about displacement fields and their derivatives, allowing for strain evaluation. This paper presents the application of the Moiré interferometry method for comprehensive characterization of the displacement field in the vicinity of a crack tip in a flat plate. The plate crack resulted from a fatigue test, and it was subjected to a three-point bending test. In the crack region, a diffraction grating with 1200 l/mm was previously applied in two orthogonal directions. After assembling the experimental setup, measurements of the displacement field were carried out for different load values. Algorithms for deriving and filtering the displacement field have been developed to calculate the strain field.