Simultaneous measurement of out-of-plane displacement and slope using a multiaperture DSPI system and fast Fourier transform

Department of Physics Applied Optics Laboratory, Indian Institute of Technology Madras, Chennai, India.
Applied Optics (Impact Factor: 1.78). 09/2007; 46(23):5680-6. DOI: 10.1364/AO.46.005680
Source: PubMed


The simultaneous quantitative measurement of out-of-plane displacement and slope using the fast Fourier transform method with a single three-aperture digital speckle pattern interferometry (DSPI) arrangement is demonstrated. The method coherently combines two sheared object waves with a smooth reference wave at the CCD placed at the image plane of an imaging lens with a three-aperture mask placed in front of it. The apertures also introduce multiple spatial carrier fringes within the speckle. A fast Fourier transform of the image generates seven distinct diffraction halos in the spectrum. By selecting the appropriate halos, one can directly obtain two independent out-of-plane displacement phase maps and a slope phase map from the two speckle images, one before and the second after loading the object. It is also demonstrated that by subtracting the out-of-plane displacement phase maps one can generate the same slope phase map. Experimental results are presented for a circular diaphragm clamped along the edges and loaded at the center.

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    • "Several spatial phase-shift digital shearography (SPS-DS) systems have been developed to measure out-of-plane strain components using only one frame of measurement . Pedrini et al [8], Bhaduri et al [9] [10], and Xie et al [11] [12] have reported several types of SPS-DS systems for the measurement of out-of-plane strain components using a single frame, solving the full-field out-of-plane dynamic strain components measurement problem. However, all those system can only measure the out-of-plane deformation gradient ∂w/∂x or ∂w/∂y under dynamic loading. "
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    ABSTRACT: Full-field in-plane strain measurement under dynamic loading by digital shearography remains a big challenge in practice. A phase measurement for in-plane strain information within one time frame has to be achieved to solve this problem. This paper presents a dual beam spatial phase-shift digital shearography system with the capacity to measure phase distribution corresponding to in-plane strain information within a single time frame. Two laser beams with different wavelengths are symmetrically arranged to illuminate the object under test, and two cameras with corresponding filters, which enable simultaneous recording of two shearograms, are utilized for data acquisition. The phase information from the recorded shearograms, which corresponds to the in-plane strain, is evaluated by the spatial phase-shift method. The spatial phase-shift shearography system realizes a measurement of the in-plane strain through the introduction of the spatial phase-shift technique, using one frame after the loading and one frame before loading. This paper presents the theory of the spatial phase-shift digital shearography for in-plane strain measurement and its derivation, experimental results, and the technique’s potential.
    Measurement Science and Technology 11/2015; 26(11):115202. DOI:10.1088/0957-0233/26/11/115202 · 1.43 Impact Factor
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    • "shows the schematic of double aperture spatial phase-shift shearography setup introduced by B. Bhaduri et al in 2006 <ref type="bibr" target="#b5" coords="4,484.94,404.05,32.28,11.09;4,63.00,415.58,20.04,11.09">[6]</ref> [7]. In this setup, the diffuse object is illuminated by a collimated laser beam. "
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    ABSTRACT: In the last decade, due to the fast development of phase-shift technique, the measurement sensitivity of digital shearography (DS) technology has been increased tens of times which brings the technology itself a wide acceptance by the industry as a practical measurement tool for quality inspection and non-destructive testing. In common sense, compare to Temporal Phase-Shift Digital Shearography (TPS-DS), Spatial Phase-Shift Digital Shearograhy (SPS-DS) has the advantage of a broader capability for both static and dynamic measurement applications while keeps the disadvantage of lower phase-map quality. Recently, with new developments, the phase map quality of spatial phase-shift digital shearography has been greatly improved which is now comparable to the temporal phase-shift technique. This article gives a review of recent developments of spatial phase-shift digital shearography. Theory, experimental setup, phase-map results and applications are shown in detail.
    International Conference on Experimental Mechanics 2014; 03/2015
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    ABSTRACT: A direct method of determining second-order derivatives of displacement (curvature and twist) using two-channel double-aperture digital shearography is presented. Spatial carrier fringes are incorporated inside the speckle using a double-aperture mask in a two-channel experimental setup. Two sets of slope phase maps are generated that are either shifted in the x direction for curvature measurement or in the y direction for twist measurement. Experimental results are presented to verify the validity of the proposed method.
    Optical Engineering 03/2010; 49(3). DOI:10.1117/1.3359470 · 0.95 Impact Factor
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