High Spatial-Resolution Digital Phase-Stepping Shearography

Abstract

Digital phase-stepping shearography is a speckle interferometric technique that uses laser speckles to generate the phase map of the displacement derivatives of a stressed object, and hence can map the stresses of a deformed object directly. Conventional digital phase-stepping shearography relies on the use of video cameras of relatively lower resolution, in the order of 5 megapixels or lower, operating at a video rate. In the present work, we propose a novel method of performing high spatial resolution phase stepping shearography. This method uses a 24 megapixel still digital imaging device (DSLR camera) and a Michelson-type shearing arrangement with an edge-clamped, center-loaded plate. Different phase-stepping algorithms were used, and all successfully generated shearograms. The system enabled extremely high-resolution phase maps to be generated from relatively large deformations applied to the test plate. Quantitative comparison of the maximum achieved spatial resolution is made with the video-rate cameras used in conventional shearography. By switching from conventional (video) imaging methods to still imaging methods, significantly higher spatial resolution (by about 5 times) can be achieved in actual phase-stepping shearography, which is of great usefulness in industrial non-destructive testing (NDT).

A Comprehensive Review on the Non-Destructive Test for Polymer Matrix Composite

“…a DSLR type with high pixel resolution, captures the image of sample twice, i.e. the first one is without load and the second one is with load [50] . After the sample is loaded, the deformation occurs and the deformation is captured then by as the second picture.…”

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High resolution phase-stepping shearography by using a 24 megapixel digital still imaging device

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