A spatial-phase-shift-based defect detection shearography system with independent adjustment of shear amount and spatial carrier frequency

Abstract

Digital shearography has a wide application in defect detection. Phase-shift-technique-based shearography has a higher phase measurement sensitivity than the real-time shearography. This phase shift technique can be divided into temporal phase shift shearography and spatial phase shift shearography. The latter has the advantage of fast detection and can be used in dynamic detection. In a traditional spatial carrier frequency shearography system, shear amount adjustments and spatial carrier frequency are not completely independent. In some shearography systems, shear amount and spatial carrier frequency are adjusted by rotating mirrors. The amounts of rotation required to obtain the appropriate shear amount and spatial carrier frequency are different, thereby reducing the accuracy of detection results. In other shearography systems, although the two adjustments are divided into two parts, using a rotating mirror to obtain the appropriate shear amount will also introduce additional spatial carrier frequency which will also have some influence on the result. This paper introduces a detection method with independently adjusting shear amount and spatial carrier frequency. Shear amount adjustment is achieved by changing the written image of a spatial light modulator (SLM). No additional spatial carrier frequency is introduced. Spatial carrier frequency is only controlled by the relative position between the dual apertures. Experimental results of undamaged and damaged specimens indicate that this system is suitable for detecting the phase distribution of the deformation and internal defects.