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Microcrack Quantification in Composite Materials by a Neural Network Analysis of Ultrasound Spectral DataIntra-ply microcracking in unlined composite pressure vessels can be very troublesome to detect and when linked through the thickness can provide leak paths that may hinder mission success. The leaks may lead to loss of pressure/propellant, increased risk of explosion and possible cryo-pumping into air pockets within the laminate. Ultrasonic techniques have been shown capable of detecting the presence of microcracking and in this work they are used to quantify the level of microcracking. Resonance ultrasound methods are utilized with artificial neural networks to build a microcrack prediction/measurement tool. Two networks are presented, one unsupervised to provide a qualitative measure of microcracking and one supervised which provides a quantitative assessment of the level of microcracking. The resonant ultrasound spectroscopic method is made sensitive to microcracking by tuning the input spectrum to the higher frequency (shorter wavelength) components allowing more significant interaction with the defects. This interaction causes the spectral characteristics to shift toward lower amplitudes at the higher frequencies. As the density of the defects increases more interactions occur and more drastic amplitude changes are observed. Preliminary experiments to quantify the level of microcracking induced in graphite/epoxy composite samples through a combination of tensile loading and cryogenic temperatures are presented. Both unsupervised (Kohonen) and supervised (radial basis function) artificial neural networks are presented to determine the measurable effect on the resonance spectrum of the ultrasonic data taken from the samples.
Document ID
20040000578
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Walker, James L.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Russell, Samuel S.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Suits, Michael W.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 2003
Subject Category
Composite Materials
Meeting Information
Meeting: ASNT Fall Conference and Quality Testing Show
Location: Pittsburgh, PA
Country: United States
Start Date: October 13, 2003
End Date: October 17, 2003
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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