A Simultaneous Multi-Directional Defects Measurement Based on Polarization-Multiplexed Four-Directional Digital Shearography With Large Field of View

Since the sensitivity of digital shearography (DS) is related to its shearing direction and the anomaly of the relative deformation is sensitive to the defect direction in non-destructive testing (NDT), traditional single- or two-direction DS systems may miss defects in some directions. To avoid missing defects, a polarization-multiplexed four-directional DS for simultaneous measurement of multi-directional defects is proposed in this article. Four object beams whose relative shearing amount and spatial carrier frequency can be adjusted independently are constructed, with which four shearograms can be obtained simultaneously in one recorded interferogram. And by embedding a 4f system in front of the interferometers to transmit the captured image, the measurement field of view (FOV) is doubled. To verify the performance of the proposed four-directional DS system, an experimental setup was constructed, and two experiments of central force loading and non-destructive thermal loading were performed. Experimental results verify that the proposed system can effectively detect defects in multiple directions simultaneously.