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Ultrasonic Characterization of Fatigue Cracks in Composite MaterialsMicrocracking in composite structures due to combined fatigue and cryogenic loading can cause leakage and failure of the structure and can be difficult to detect in-service. In aerospace systems, these leaks may lead to loss of pressure/propellant, increased risk of explosion and possible cryo-pumping. The success of nondestructive evaluation to detect intra-ply microcracking in unlined pressure vessels fabricated from composite materials is critical to the use of composite structures in future space systems. The work presented herein characterizes measurements of intraply fatigue cracking through the thickness of laminated composite material by means of correlation with ultrasonic resonance. Resonant ultrasound spectroscopy provides measurements which are sensitive to both the microscopic and macroscopic properties of the test article. Elastic moduli, acoustic attenuation, and geometry can all be probed. The approach is based on the premise of half-wavelength resonance. The method injects a broadband ultrasonic wave into the test structure using a swept frequency technique. This method provides dramatically increased energy input into the test article, as compared to conventional pulsed ultrasonics. This relative energy increase improves the ability to measure finer details in the materials characterization, such as microcracking and porosity. As the microcrack density increases, more interactions occur with the higher frequency (small wavelength) components of the signal train causing the spectrum to shift toward lower frequencies. Several methods are under investigation to correlate the degree of microcracking from resonance ultrasound measurements on composite test articles including self organizing neural networks, chemometric techniques used in optical spectroscopy and other clustering algorithms.
Document ID
20020068101
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Workman, Gary L.
(Alabama Univ. Huntsville, AL United States)
Watson, Jason
(Alabama Univ. Huntsville, AL United States)
Johnson, Devin
(Alabama Univ. Huntsville, AL United States)
Walker, James
(NASA Marshall Space Flight Center Huntsville, AL United States)
Russell, Sam
(NASA Marshall Space Flight Center Huntsville, AL United States)
Thom, Robert
Date Acquired
August 20, 2013
Publication Date
January 1, 2002
Subject Category
Space Processing
Meeting Information
Meeting: 11th International Symposium on Nondestructive Characterization of Materials
Location: Berlin
Country: Germany
Start Date: June 24, 2002
End Date: June 28, 2002
Funding Number(s)
CONTRACT_GRANT: NAG8-1548
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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