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Proceedings Paper

Fatigue crack detection in a plate girder using Lamb waves
Author(s): D. W. Greve; I. J. Oppenheim; Wei Wu; Peng Zheng
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Paper Abstract

We report on the application of wafer-type PZT transducers to the detection of flaws in steel plate girders. In these experiments one transducer is used to emit a pulse and the second receives the pulse and reflections from nearby boundaries, flaws, or discontinuities (pitch-catch mode). In this application there will typically be numerous reflections observed in the undamaged structure. A major challenge is to recognize new reflections caused by fatigue cracks in the presence of these background reflections. A laboratory specimen plate girder was fabricated at approximately half scale, 910 mm deep with an h/t ratio of 280 for the web and a b/t ratio of 16 for the flanges, and with transverse stiffeners fabricated with a web gap at the tension flange. Two wafer-type transducers were mounted on the web approximately 175 mm from the crack location, one on each side of the stiffener. The transducers were operated in pitch-catch mode, excited by a windowed sinusoid to create a narrowband transient excitation. The transducer location relative to the crack corresponded to a total included angle of roughly 30 degrees in the path reflecting from the crack. Cyclic loading was applied to develop a distortion-induced fatigue crack in the web at the web gap location. After appearance of the crack, ultrasonic measurements were performed at a range of center frequencies below the cutoff frequency of the A1 Lamb wave mode. Subsequently the crack was extended mechanically to simulate crack growth under primary longitudinal (bending) stress and the measurements were repeated. Direct differencing of the signals showed arrivals at times corresponding to reflection from the crack location, growing in amplitude as the crack was lengthened mechanically. These results demonstrate the utility of Lamb waves for crack detection even in the presence of numerous background reflections.

Paper Details

Date Published: 10 April 2007
PDF: 12 pages
Proc. SPIE 6529, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2007, 65291W (10 April 2007); doi: 10.1117/12.715359
Show Author Affiliations
D. W. Greve, Carnegie Mellon Univ. (United States)
I. J. Oppenheim, Carnegie Mellon Univ. (United States)
Wei Wu, Carnegie Mellon Univ. (United States)
Peng Zheng, Carnegie Mellon Univ. (United States)

Published in SPIE Proceedings Vol. 6529:
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2007
Masayoshi Tomizuka; Chung-Bang Yun; Victor Giurgiutiu, Editor(s)

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