Non-destructive testing and evaluation using phase shifting electronic shearography

In this paper, a phase shifting electronic shearography technique and its application in nondestructive testing (NDT) is described. Electronic shearography or Digital Speckle Shearing Interferometry (DSSI) has found applications as an NDT tool in industrial environments due to its less stringent vibration isolation requirement and simple optical set-up. Moreover, it relies on changes in displacement gradient and so measurements are not masked by overall movement of the specimen. One of the main problems in DSSI is that it is not easy to obtain high-contrast fringe patterns under certain conditions. To solve the problem, an applicable computer-controlled phase shift technique is developed and is shown to yield good quality phase contours of a deformed object. In addition, it allows the displacement derivative at all points on the object to be quantified. This capability leads to the easy and rapid determination of the location, size, and shape of a defect. Experimental results of detection of internal flaws in pipes based on the above system are presented.