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This paper presents a simple spatial phase shift shearography based on the Michelson interferometer. The Michelson interferometer based shearographic system has been widely utilized in industry as a practical nondestructive test tool. In the system, the Michelson interferometer is used as a shearing device to generate a shearing distance by tilting a small angle in one of the two mirrors. In fact, tilting the mirror in the Michelson interferometer also generates spatial frequency shift. Based on this feature, we introduce a simple Michelson interferometer based spatial phase shift shearography. The Fourier transform (FT) method is applied to separate the spectrum on the spatial frequency domain. The phase change due to the loading can be evaluated using a properly selected windowed inverse-FT. This system can generate a phase map of shearography by using only a single image. The effects of shearing angle, spatial resolution of couple charge device camera, and filter methods are discussed in detail. The theory and the experimental results are presented.

The main applications of temporal phase shift shearography are in NDT and strain measurement. Temporal Phase Shift Shearography for NDTThe most important application of temporal phase shift shearography, called digital shearography for simplicity, is for NDT, which enables flaws in objects/ materials to be found without damaging them. Compared to conventional NDT methods, such as ultrasonic, radiographic, magnetic article, dye penetrant, eddy current, and acoustic emission methods, digital shearography has the advantages of full-field measurement, high sensitivity, easy visualization, quick measurement speed, and real-time display of test results. Due to these distinct advantages, digital shearography has been widely accepted by the automotive and aerospace industries as a recommended NDT method for rubber and composite materials.1-2 The details of digital shearography for NDT have been described and discussed in Refs. 3 and 4. In this section, potentials and limitations of temporal phase shift shearography for NDT are reviewed, practical applications using different loading methods are demonstrated, and a few recent developments, such as NDT for testing relatively large objects and for measuring mirror-like surfaces, are presented and discussed.

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