Review of Shearography for Dual-Directional Measurement

Abstract

Shearography is a coherent optical technique that allows the identification of the first derivative of deformation in the shearing direction. Due to direct measuring strain information, shearography is suited for non-destructive testing and evaluation (NDT/NDE). However, if there is a small defect parallel to the shearing direction, the first derivative of deformation in the direction has no noticeable change, and the defect is not visible. Therefore, the development of a shearography system with dual-directional simultaneous measurement of the first derivatives of deformation both in x- and y-directions is highly demanded in the field of NDT/NDE. It is suited to inspect complicated defects, such as long and narrow slots, microcracks, etc. This paper presents a review of shearography for different dual-directional systems developed in the last two decades. After a brief overview of shearography, the paper will display two dual-directional shearographic techniques—temporal phase-shift (TPS) and spatial phase-shift (SPS) methods. TPS dual-shearing systems are suited for static measurements, while the SPS dual-shearing systems are useful for dynamic measurements. The basic theories, optical layouts, and comparisons are presented. The advantages and disadvantages of practical applications are discussed.

Accurate determination of the elastic moduli of optimized cantilever beams by efficient time-averaged ESPI system

“…To determine the oscillating shape of the object, however, the spatial density of probes should be increased. Modern photomechanical methods, equipped with chargecoupled device (CCD)/complementary metal oxide semiconductor (CMOS) camera recordings significantly overcome the limitations of low spatial resolution [11][12][13][14][15][16], amongst which the electronic speckle pattern interferometry (ESPI) is of advantages of full-field, non-contact, high sensitivity, etc, and has been widely used in parameter identification. Through the bulge test combined ESPI observation system, Miao et al [17] obtained the continuous out-of-plane displacement and current load of nanoporous alumina membrane.…”

“…Therefore, the identification of natural frequencies of the object based on recognizing the density of the fringes of the mode shape is rough and laborious, which will further increase the calculation errors of the elastic moduli. In contrast, an analogical technology, shearography, used to detect the slope of the out-of-plane deflection, is famous for its excellent anti-interference capability, because of the quasicommon optical path arrangement [12,31,32]. To combine the advantages of these two techniques, in this study, the shear optical path arrangement was improved to monitor the out-ofplane deflection of the cantilever beam.…”