Non-destructive measurement of internal defects using shear laser interferometry method

Digital shearography is a laser interferometry method that is used to detect and measure defects non-destructively. In this study, a new approach was presented to measure planar defects using digital shearography method. A total of 16 shearography tests were carried out in order to verify the proposed method and study the effect of shear size and depth of defect on measurement accuracy. Defect size was varied in four level and depth of defect and shear size were changed in two levels. The defects size were measured in different conditions and the estimation error was obtained in each case. The proposed method was able to predict defect size with good precision and the lowest error percentage was obtained in 15 mm size 0.5 mm depth defect at shear size of 15 mm. The results showed that as the shear size is approached the defect size, the error percentage is reduced and the maximum accuracy of prediction is obtained when the shear size is equal to the size of the defect. Also, varying the depth of defect led to variation of estimation error, and in most cases the prediction of defect size with a depth of 1 mm was more precisely due to the better shape of the shearography fringes.