Shearography In Nondestructive Testing Research Articles

A novel phase shift technique in shearography for NDT

Digital shearography (DS) is a whole-field non-contacting optical method for nondestructive testing (NDT) of subsurface flaws and strain measurement. In this paper, we describe a novel phaseshifting technique in DS for nondestructive evaluation (NDE) and NDT of quasi dynamic behaviour of objects subject to varying loads. A Wollaston lens, a precise wave plate device and a polariser are employed to introduce constant phase differences between two shearing wavefronts. The wave plate device is in front of the polariser, which has a transmissive wavefront distortion of less than 1/8 wavelength. Phase difference can be adjusted by rotating the polariser. The rotation for angle adjusting can be easily carried out according to the requirement of the phase shifting. In this technique, the phase shifting is performed only on the static images of the object before deformation or loading. By setting the angle of the polariser to 0º, -60º and 60º, three speckle patterns with the defined phase differences are captured, and are referred to as initial speckle patterns I1,0, I1,-60 and I1,60. Afterwards, the polariser is reset to 0º before loading. The speckle pattern I0 is treated as a base pattern, and will be subtracted from the subsequent speckle patterns which are captured in the quasi dynamic deformation process.

Application of shearography in nondestructive testing of composite plates

Shearography is an interferometric method which provides a whole-field observation of isoclines which are related to surface strains. Since defects in structures such as cracks and delamination induce strain concentrations when the structures are loaded, shearography reveals defects from anomalies in the interferometric fringes. This paper illustrates the use of shearography for estimating the size and depth of disbonds in glassfibre reinforced plastic plates. Square flaws of known sizes are deliberately created within the plates and the “vacuum stressing” method is used to load the defective plates. Results show that disbonds in the plates can be easily sized from the boundaries of the anomalous fringe patterns, and their depths can also be estimated from the number of fringes which appear within the defective areas.

Application of shearography in nondestructive testing of composite plates

Shearography is an interferometric method which provides a whole-field observation of isoclines which are related to surface strains. Since defects in structures such as cracks and delamination induce strain concentrations when the structures are loaded, shearography reveals defects from anomalies in the interferometric fringes. This paper illustrates the use of shearography for estimating the size and depth of disbonds in glassfibre reinforced plastic plates. Square flaws of known sizes are deliberately created within the plates and the “vacuum stressing” method is used to load the defective plates. Results show that disbonds in the plates can be easily sized from the boundaries of the anomalous fringe patterns, and their depths can also be estimated from the number of fringes which appear within the defective areas.