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13 May 2000 Implementation of temporal-phase unwrapping in a real-time phase-stepped shearing speckle interferometer
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The implementation of temporal phase unwrapping within a real- time phase stepped shearing speckle interferometer is presented. Speckle phase maps obtained with a shearing speckle interferometer, representing an object before and after deformation, reveal sub-surface defects or damage, after subtracting the images. Phase information is only known modulo 2(pi) , and has to be unwrapped for a true representation of the deformation map. Results are easier to interpret during the deformation process when the images are unwrapped; phase unwrapping also facilitates automatic detection of suspected areas. It is shown that, compared to the more common spatial* phase unwrapping methods, temporal phase unwrapping is much faster, and can be implemented in a real-time system. In addition, this method offers an increased measuring range, reduces sensitivity for speckle decorrelation, handles discontinuities in the object, and is very reliable, even when used with noisy data. Processing strategies for the selective removal of unwanted image components, and for automatic defect detection are presented. Examples of results obtained for artificial defects in metallic and composite aeronautical components are shown. Measurements have been carried out with our phase stepped shearography system under laboratory and industrial conditions, showing improved performance under non- ideal conditions. It has been shown during these experiments that shearography cannot only be used for detection of defects, but also for characterization.
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Peter A. A. M. Somers and Hedser H. van Brug "Implementation of temporal-phase unwrapping in a real-time phase-stepped shearing speckle interferometer", Proc. SPIE 3993, Nondestructive Evaluation of Aging Materials and Composites IV, (13 May 2000);

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