Detection of Sub-surface Defects in Polymer Materials using Digital Shearography Method with Different loading and set-up parameters

Digital Shearography or Laser interferometry is a novel non-destructive evaluating method based on laser beam which has been used and developed for measurement of first derivative of surface displacement directly. This method is equivalent to a full-area strain gauge that allows you to observe the strain distribution over a large area. Shearography is used for non-destructive inspection of various materials. In this paper, the application of Digital Shearography method is investigated in detection of subsurface cracks inside lightweight Polyvinyl chloride specimens as one of the polymeric materials. Shear distance, shear direction and loading size are the most three effective parameters in evaluating cracks by this method. Thus, after introducing and preparing a propriate setup, the effect of the main parameters including the distance and direction of shear and the amount of loading for different cracks in polymeric plates were investigated. The results show that the quality of fringe patterns is much higher when the shear distance is half the crack length and perpendicular to the crack direction. Also, the loading range is different for each crack and the optimal amount needs to obtain for each type of material.