Browsing by Author "Fu, S."

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    Combined shearography and speckle pattern photography for single-access multi- component surface strain measurement
    (International Society for Optical Engineering; 1999, 2003-12-31T00:00:00Z) Groves, Roger M.; James, Stephen W.; Tatam, Ralph P.; Fu, S.; Shen, Gongxin X.; Cha, Soyoung S.; Chiang, F. P.; Mercer, Carolyn R.
    Full surface strain measurement requires the determination of two out-of-plane and four in-plane displacement gradient components of the surface strain tensor. Shearography is a full-field speckle interferometry technique with a sensitivity predominately to the out-of-plane displacement gradient. Speckle pattern photography has the sensitivity to the in-plane displacement, and taking the derivative yields the in-plane displacement gradient. In this paper the two techniques are combined to yield a single-access multi-component surface strain measurement using shearography to measure the out-of-plane components and speckle pattern photography to measure the in-plane components. Results are presented of a multi-component surface strain measurement.
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    Single-axis combined shearography and digital speckle photography instrument for full surface strain characterization
    (Spie -- the Int Soc for Optical Engineering, 2005-02-28T00:00:00Z) Groves, Roger M.; Fu, S.; James, Stephen W.; Tatam, Ralph P.
    Full characterization of the surface strain requires the measurement of six displacement gradient components of the surface strain tensor. The out-of-plane displacement gradient component may be directly measured using the full-field speckle interferometry technique of shearography, but to fully characterize the surface strain using shearography, a minimum of three illumination, or viewing, directions are required. The image processing technique of digital speckle photography (DSP) is sensitive to in-plane displacement for normal collinear illumination and viewing, with the displacement gradient components obtained by differentiation. A combination of shearography and digital speckle photography is used to perform full characterization of the surface strain using a single illumination and viewing direction. The increase in complexity compared with a standard single-channel shearography system lies predominantly in the additional image processing requirements. Digital speckle photography image processing is performed using the optical flow field technique and the advantages of this technique compared with correlation are discussed. The design of the instrument is described and full surface strain measurements made with the system are presented.