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See detailAn in-line shearography setup based on circular polarization gratings
Blain, Pascal ULg; Piron, Pierre ULg; Renotte, Yvon ULg et al

in Optics & Lasers in Engineering (2013)

The shearing amount defines the resolution of a speckle shearing interferometer and the shearing direction defines the sensitivity direction of the setup. The properties of circular (cycloid) holographic ... [more ▼]

The shearing amount defines the resolution of a speckle shearing interferometer and the shearing direction defines the sensitivity direction of the setup. The properties of circular (cycloid) holographic polarization gratings recorded in liquid crystal polymers can be used to build a new multi-shearing direction and amount shearography setup. The polarization states of the diffracted beams offer an easy way to produce phase shifts and thus to compute the phase contained in the shearograms. The theoretical bases of such a device are highlighted and an original compact and full in-line setup is proposed. First experimental results of delamination detection and flaw detection by shearography are presented. A discussion on the importance of the grating recording and the polarization orientation points out the best working requirements. [less ▲]

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See detailQuality assessment of speckle patterns for digital image correlation
Lecompte, D.; Smits, A.; Bossuyt, Sven et al

in Optics & Lasers in Engineering (2006), 44(11), 1132-1145

Digital image correlation (DIC) is an optical–numerical full-field displacement measuring technique, which is nowadays widely used in the domain of experimental mechanics. The technique is based on a ... [more ▼]

Digital image correlation (DIC) is an optical–numerical full-field displacement measuring technique, which is nowadays widely used in the domain of experimental mechanics. The technique is based on a comparison between pictures taken during loading of an object. For an optimal use of the method, the object of interest has to be covered with painted speckles. In the present paper, a comparison is made between three different speckle patterns originated by the same reference speckle pattern. A method is presented for the determination of the speckle size distribution of the speckle patterns, using image morphology. The images of the speckle patterns are numerically deformed based on a finite element simulation. Subsequently, the displacements are measured with DIC-software and compared to the imposed ones. It is shown that the size of the speckles combined with the size of the used pixel subset clearly influences the accuracy of the measured displacements. [less ▲]

Detailed reference viewed: 188 (1 ULg)