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10 November 2003 Multi-component pulsed-laser shearography using optical fiber imaging-bundles
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Shearography is a full-field non-contact optical technique usually used for the identification of the location of defects in non-destructive testing. Shearography is sensitive to displacement gradient, a parameter closely related to the surface strain. To fully characterise the surface strain requires the determination of six orthogonal components of displacement gradient and this is achieved in shearography by measuring from three, or more, illumination, or viewing, directions and from a minimum of two directions of applied shear, followed by a coodinate transformation to the orthogonal components. In this paper the authors use illumination from a single direction using dual pulsed injection-seeded Nd:YAG lasers, and view the object from four directions. The images from the four viewing directions are ported to a single interferometer head using a four-leg optical fiber imaging bundle. At the interferometer head the four views are spatially-multiplexed into a single image, pass through the interferometer head and are recorded by a single high resolution dual-framing camera. The direction of applied shear in the interferometer head is adjustable to allow measurements from the two shear directions. Experimental results are presented of displacement gradient from this pulsed laser shearography instrument.
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Roger M. Groves, Stephen W. James, and Ralph P. Tatam "Multi-component pulsed-laser shearography using optical fiber imaging-bundles", Proc. SPIE 5191, Optical Diagnostics for Fluids, Solids, and Combustion II, (10 November 2003);

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