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Development of Natural Flaw Samples for Evaluating Nondestructive Testing Methods for Foam Thermal Protection SystemsLow density polyurethane foam has been an important insulation material for space launch vehicles for several decades. The potential for damage from foam breaking away from the NASA External Tank was not realized until the foam impacts on the Columbia Orbiter vehicle caused damage to its Leading Edge thermal protection systems (TPS). Development of improved inspection techniques on the foam TPS is necessary to prevent similar occurrences in the future. Foamed panels with drilled holes for volumetric flaws and Teflon inserts to simulate debonded conditions have been used to evaluate and calibrate nondestructive testing (NDT) methods. Unfortunately the symmetric edges and dissimilar materials used in the preparation of these simulated flaws provide an artificially large signal while very little signal is generated from the actual defects themselves. In other words, the same signal are not generated from the artificial defects in the foam test panels as produced when inspecting natural defect in the ET foam TPS. A project to create more realistic voids similar to what actually occurs during manufacturing operations was began in order to improve detection of critical voids during inspections. This presentation describes approaches taken to create more natural voids in foam TPS in order to provide a more realistic evaluation of what the NDT methods can detect. These flaw creation techniques were developed with both sprayed foam and poured foam used for insulation on the External Tank. Test panels with simulated defects have been used to evaluate NDT methods for the inspection of the External Tank. A comparison of images between natural flaws and machined flaws generated from backscatter x-ray radiography, x-ray laminography, terahertz imaging and millimeter wave imaging show significant differences in identifying defect regions.
Document ID
20070036794
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Workman, Gary L.
(Alabama Univ. Huntsville, AL, United States)
Davis, Jason
(Alabama Univ. Huntsville, AL, United States)
Farrington, Seth
(Alabama Univ. Huntsville, AL, United States)
Walker, James
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Date Acquired
August 24, 2013
Publication Date
October 22, 2007
Subject Category
Quality Assurance And Reliability
Meeting Information
Meeting: 4th Pan-American Conference for NDT
Location: Buenos Aires
Country: Argentina
Start Date: October 22, 2007
End Date: October 26, 2007
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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