Fast Nondestructive Testing Under Dynamic Loading

Posted: 2013-11-12

http://spie.org...ticleID=x104532

Digital shearography—also called digital speckle pattern shearing interferometry —has been widely accepted by industry as an efficient non-destructive testing (NDT) tool for composite material. A laser illuminates the object under test, and the speckle pattern reflected from its surface is recorded. This is repeated when the test object is under stress, and the stressed and unstressed speckle patterns are compared to produce a fringe pattern.

The gradient of a deformation field is measured directly in digital shearography, and near-surface defects are found by recognizing specific ‘butterfly’ patterns on the phase map created by phase-shift digital shearography. However, the low acquisition rate of traditional temporal phase-shift-based digital shearography (usually 1–2Hz due to multiple phase-shift steps in the temporal domain) has limited its application to static or quasi-static loading situations.1,2 We developed a novel spatial phase-shift digital shearography system, using the spatial frequency carrier method and a simple Michelson interferometer setup for dynamic loading.

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