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Optical Engineering

Interferometric and holographic imaging of surface-breaking cracks
Author(s): James L. Blackshire; Bradley D. Duncan
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Paper Abstract

Two advanced nondestructive evaluation systems are developed for imaging surface-breaking cracks in aerospace materials. The systems use scanning heterodyne interferometry and frequency-translated holography principles to image ultrasonic displacement fields on material surfaces with high resolution and sensitivity. Surface-breaking cracks are detected and characterized by visualizing near-field ultrasonic scattering processes, which in turn results in local intensification of ultrasonic displacement fields in the immediate vicinity of a crack. The local intensification permits cracks to be easily distinguished from background levels, and creates unique displacement field images that follow the contours and morphology of the cracks with microscopic precision. The interferometric and holographic imaging approaches each provide noncontact and near optical-diffraction-limited measurement capabilities that are essential for probing ultrasonic displacement fields in the immediate vicinity of cracks. Several representative crack-imaging results are provided, along with detailed descriptions of both experimental techniques, and the capabilities and limitations of each method. The resulting systems provide simple yet very powerful tools for evaluating surface-breaking cracks in detail.

Paper Details

Date Published: 1 June 2004
PDF: 9 pages
Opt. Eng. 43(6) doi: 10.1117/1.1731201
Published in: Optical Engineering Volume 43, Issue 6
Show Author Affiliations
James L. Blackshire, Air Force Research Lab. (United States)
Bradley D. Duncan, Univ. of Dayton (United States)


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