Electronic Shearography: Current Capabilities, Potential Limitations, and Future Possibilities for Industrial Nondestructive Inspection

Abstract

Image-shearing speckle pattern interferometry, more commonly referred to as ‘shearography’, is a full-field, laser-based interferometric technique first developed for applications in experimental mechanics [1,2]. Shearography is sensitive to derivatives of the out-of-plane surface displacement of a body under load, as opposed to other full-field methods such as holographic interferometry and conventional speckle pattern interferometry, which typically contour the surface displacement directly [3]. The early shearography experiments used high-resolution photographic film to record images of the laser speckle patterns. In contrast to traditional film-based techniques, electronic shearography uses an electronic camera for image recording [4]. This technology, commercially available for the past several years, has received much interest within the NDE community because of its potential for rapid, non-contacting optical inspection of large areas. While there are advantages and disadvantages specific to either imaging medium, electronic shearography is the clear choice for industrial inspection because image acquisition and processing is accomplished at a video frame rate of 30 Hz to produce shearographic fringe patterns in real time. Real-time inspection is not possible with film- based shearography, which requires time-consuming development of the filmplate and optical high pass filtering for readout of the fringe patterns.