Identification of Flaws Using Digital Shearography

摘要

Digital shearography is a whole-field non-contact optical technique, which has been widely used for detecting flaws in non-destructive testing (NDT). In digital shearography, flaws are usually detected based on the abnormity of fringes obtained when the derivative of displacement at the area with flaw is much larger than at the area without flaw. However, there are many flaws which are difficult to be identified directly from the distribution of fringes in digital shearography. Therefore, a new method is proposed to detect these flaws difficult to be identified in this paper. The proposed method can be used to detect the flaws located inside an object, which are difficult to be identified from the distribution of fringes in digital shearography, based on the distribution of the second derivative of displacement. Though the proposed method can not be used to accurately determine the size and shape of a flaw located inside an object because of the complexity of both the flaw and the material used, it can still be used for analyzing the existence and the position of a flaw inside the object. Both theoretical analysis and experimental verification are presented in the paper, and the result obtained in the paper has shown that the theoretical analysis and the experimental verification are in a good agreement.