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31 May 1999 Detection and characterization of damage in composite plates using shearography and wave-based acoustic emission techniques
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This paper investigates the use of shearography and waveform- based acoustic emission (AE) techniques to detect and assess damage in composite plates due to high velocity impact. Five 48-ply [0/+45/90/-45]6s laminated AS4/PEEK composite plates donated by Boeing Company in St. Louis were used as test specimens. Shearography images of all five test specimens were taken before impact testing to detect any pre- existing internal damage from fabrication. Three broadband AE sensors were mounted on the surface of the composite plates to measure AE signals due to impact. High velocity impact tests of plates with all four edges clamped were conducted using a gas gun facility. The AE sensor signals were instantaneously acquired during the impact tests and stored in a Pentium computer. The digitized AE signals were processed in time and frequency domains. The raw AE signals were preprocessed to remove reflections from the plate boundaries that distort the wave form and cause errors. The resulting damage due to impact was evaluated using shearography fringe patterns and AE sensor signal features. The results show a correlation of AE parameters such as AE energy, AE amplitude, AE count, and shearography fringe patterns with impact energy and impact damage of the composite plates. The AE signals show the presence of both extensional and flexural wave modes with flexural wave the dominant mode. There is quite a distinctive difference between shearography fringe patterns of undamaged and damaged composite plates.
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Anthony Chukwujekwu Okafor, Andrew W. Otieno, Vittal S. Rao, and R. Parvataneni "Detection and characterization of damage in composite plates using shearography and wave-based acoustic emission techniques", Proc. SPIE 3670, Smart Structures and Materials 1999: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, (31 May 1999);

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