Holographic Fringe Linearization Interferometry (FLI) For Defect Detection Part I The Basic Concept

G. O. Reynolds; D. A. Servaes; L. Ramos-Izquierdo; J. B. DeVelis

doi:10.1117/12.946281

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12 June 1985 Holographic Fringe Linearization Interferometry (FLI) For Defect Detection Part I The Basic Concept

G. O. Reynolds, D. A. Servaes, L. Ramos-Izquierdo, J. B. DeVelis

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Proceedings Volume 0523, Applications of Holography; (1985) https://doi.org/10.1117/12.946281
Event: 1985 Los Angeles Technical Symposium, 1985, Los Angeles, United States

Abstract

In normal double exposure holography with impulse loading it is very difficult to locate defects because the fringe clutter, due to random motion between exposures, often swamps the fringe shifts caused by the presence of sub-surface defects (cracks, debonds, etc.). We attempted to simplify the defect location problem by developing a concept more amenable to automatic readout techniques. Our approach to incorporate this change is quite simple. We swing the object beam between the two exposures which adds a linear fringe to the reconstructed image. Proper selection of the fringe frequency (angle of object beam swing) and the loading force creates a recon-structed image laced with linear fringes with fringe shifts at the defect locations which are highly visible. We will describe the theory of the process. Experiments performed with a static load illustrate that the defect is seen as fringe shifts on a linear carrier. Both through cuts and rear surface cuts in a metal test plate were used to simulate defects. We further show that the defects have characteristic Fourier signatures different from those of the carrier.

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G. O. Reynolds, D. A. Servaes, L. Ramos-Izquierdo, and J. B. DeVelis "Holographic Fringe Linearization Interferometry (FLI) For Defect Detection Part I The Basic Concept", Proc. SPIE 0523, Applications of Holography, (12 June 1985); https://doi.org/10.1117/12.946281

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