Browsing by Author "Groves, Roger M."

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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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    Development of shearography for surface strain measurement of non-planar objects
    (Cranfield University, 2001-12) Groves, Roger M.; Tatam, Ralph P.
    The subject of this thesis is the development of optical instrumentation for surface strain measurement of non-planar objects. The speckle interferometry technique of shearography is used to perform quantitative measurements of surface strain on nonplanar objects and to compensate these measurements for the errors that are due to the shape and slope of the object. Shearography is an optical technique that is usually used for defect location and for qualitative strain characterisation. In this thesis a multi-component shearography system is described that can measure the six components of displacement gradient. From these measurements the surface strain can be fully characterised. For non-planar objects an error is introduced into the displacement gradient measurement due to the variation of the sensitivity vector across the field of view and the variation in the magnitude of applied shear due to the curvature of the object surface. To correct for these errors requires a knowledge of the slope and shape of the object. Shearography may also be used to measure object slope and shape by a source displacement technique. Therefore slope, shape and surface strain may be measured using the same optical system. The thesis describes a method of multiplexing the shear direction using polarisation switching, a method of measuring the source position using shadow Moire and the shearography source displacement technique for measuring the surface slope and shape of objects. The multi-component shearography system is used to perform measurements of the six components of surface strain, on an industrial component, with a correction applied for errors due to the shape and slope of the object.
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    Full surface strain measurement using shearography
    (International Society for Optical Engineering; 1999, 2001-12-31T00:00:00Z) Groves, Roger M.; James, Stephen W.; Tatam, Ralph P.
    Shearography is a full-field optical technique usually used for the determination of surface strain. Correlation of interferometric speckle patterns recorded before and after the object deformation yields fringes sensitive to displacement gradient, from which the surface strain can be calculated. A full analysis of the surface strain requires the measurement of six displacement gradient components, using three illumination directions and two directions of applied shear. Additionally shearography may be used to measure surface slope by correlation of interferograms obtained before and after a source displacement to yield fringes sensitive to surface slope. Integration of the slope yields the object shape. In this paper shearography is used to measure the six components of displacement gradient of a gas main pipe under pressure, the surface slope of the pipe and the shape of the pipe. The object slope and shape are used to correct the displacement gradient measurements for variation in sensitivity vector across the object surface and for sensitivity variations due to the dependence of the applied shear upon the local slope of the object surface. A coordinate transformation, incorporating the object shape information, is used to obtain the in-plane and out-of-plane displacement gradients relative to the local profile of the surface.
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    Multi-component shearography using optical fibre imaging-bundles
    (International Society for Optical Engineering; 1999, 2003-12-31T00:00:00Z) Groves, Roger M.; James, Stephen W.; Tatam, Ralph P.; Wolfgang, Osten; Malgorzata, Kujawinska; Katherine, Creath
    Shearography is a full-field non-contact optical technique usually used for the investigation of defects in nondestructive testing. In shearography interferometric speckle patterns recorded before and after object deformation are correlated, often by subtraction, to yield correlation fringes sensitive to displacement gradient, a parameter closely related to surface strain. Shearography is sensitive to the component of displacement gradient that is determined by the direction of the illumination and viewing directions, the optical wavelength and by the magnitude and direction of the applied shear. To perform a multi-component measurement requires illumination, or viewing, from a minimum of three directions, followed by a coordinate transformation to obtain the in-plane and out-of-plane displacement gradient components. This would normally require the use of either multiple optical sources or multiple interferometer heads and multiple cameras. In this paper the authors use a single laser source, a single interferometer head and camera, with four views of the object ported from the camera lenses to the interferometer using a four-leg optical fibre imaging bundle. This approach allows four components of displacement gradient to be recorded simultaneously. Experimental results from the multi-component shearography instrument are presented.
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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.