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Title: Shearographic NDT of joined surfaces using multiple-frequency sweep
Authors: Hung, Y.Y. 
Shang, H.M. 
Keywords: Diagnostic map
Multiple frequency sweep
Non-destructive testing (NDT)
Time-average holography
Issue Date: 2001
Citation: Hung, Y.Y., Shang, H.M. (2001). Shearographic NDT of joined surfaces using multiple-frequency sweep. Proceedings of SPIE - The International Society for Optical Engineering 4317 : 321-326. ScholarBank@NUS Repository.
Abstract: Shearography, which enables direct measurement of surface slopes under lax environmental stability, is a practical optical tool for measurement and inspection. When applied to flaw detection, conventional shearography requires recording of two sheared-images of the test structure using an image-shearing camera - one before and another after the application of quasi-static load-increment. The resulting phase-change will be perturbed at the region where a flaw is present, when compared with that of a defect-flee identical test structure. With time-average shearography, the test object is subjected to vibrational excitation, and this is useful for inspecting open-boundaried delaminations. A major drawback with the use of single excitation frequency is the need to vibrate the test object within an appropriate frequency range, as otherwise the test data obtained will not readily reveal the defect. This paper describes a new method, based on the use of multiple frequency sweep, which addresses this concern. Th e Diagnostic Map that is proposed in this paper also enables rapid detection and unambiguous assessment of the soundness of adhesive and mechanically fastened joints. Thus, the user can conduct tests with little training received.
Source Title: Proceedings of SPIE - The International Society for Optical Engineering
ISSN: 0277786X
DOI: 10.1117/12.429594
Appears in Collections:Staff Publications

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