Quantitative defect size estimation in shearography inspection by wavelet transform and shear correction

Abstract

Despite its capability of measuring out of plane displacement gradients in the sub-micrometer range, and the possibility of successfully detecting defects (delaminations, debondings, impacts) without compromising the investigated structure (which is very important in the aerospace field), Shearography usually remains a qualitative technique. This is due to several uncertainty sources and the difficulty of managing its output images in order to extract information about the defect. The proposed methodology aims to reduce uncertainty on shear estimation, calculating the local shearing amount over a defect, and to quantify the defect size and shape, scanning its unwrapped phase-map using a wavelet transform algorithm. A PVC specimen with known defects was used to estimate the accuracy of the methodology, and a carbon fiber composite panel for aeronautical use was exploited to test the real defect reconstruction.