NDT capability of digital shearography for different materials

In this paper, the capabilities of shearography for detecting hole and crack type defects in polymeric and metallic materials using thermal loading were investigated. In order to improve the ability of the identifying defect, the fringe multiplication technique was applied to some suspectable shearography fringe patterns. Based on the test results empirical rules for inspection plates of different material with specific thicknesses were established. For aluminium plates with thicknesses of 3 mm, minimum diameter of a surface breaking hole which is detectable is approximately equal to 2.5–3.0 times the depth of the defect, and for polymer plates with a thickness of 10 mm, the minimum detectable diameter is 0.8–1.3 times of the depth. For polymeric materials results from the increasing temperature period are approximately the same as those from the decreasing temperature period. When the orientation of the image shearing is not perpendicular to the longitudinal direction of the crack type defects, the sensitivity for defect detection is relatively higher than with perpendicular image shearing.