Effect of shear distance on the shearography fringe patterns in the PVC curved surfaces

Digital shearography test is an optical and full-field method that improves the ability to identify defects with the help of image processing methods. In this method, the displacement derivatives are obtained directly from the fringe patterns, which require the extraction of phase information from the image. One of the most important parameters of the shearography method is shear distance, choosing an inappropriate shear distance, makes the procedure of detection impossible. by considering different shear distances along a curved surface contrary to a flat surface, it would be necessary to consider the correct shear distance to achieve a better result. A lot of workpieces and parts especially in petroleum industry and Aerospace have a curved surface, whereas defect detection is a crucial and important matter in these areas, it must be considering that some defects cannot be seen or detected by implementing just flat surfaces’ experiment procedure, thus some correction must be applied to tests. In this paper corrosion defect as a common de+fect in pipes has been studied and in pvc pipes experimented. Effect of angle on observation and also on shear distance has been studied. Comparison between zero degree and maximum angle which could be implemented has been conducted.