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Replica-based Crack InspectionA surface replica-based crack inspection method has recently been developed for use in Space Shuttle main engine (SSME) hydrogen feedline flowliners. These flowliners exist to ensure favorable flow of liquid hydrogen over gimble joint bellows, and consist of two rings each containing 38 elongated slots. In the summer of 2002, multiple cracks ranging from 0.1 inches to 0.6 inches long were discovered; each orbiter contained at least one cracked flowliner. These long cracks were repaired and eddy current inspections ensured that no cracks longer than 0.075 inches were present. However, subsequent fracture-mechanics review of flight rationale required detection of smaller cracks, and was the driving force for development of higher-resolution inspection method. Acetate tape surface replicas have been used for decades to detect and monitor small cracks. However, acetate tape replicas have primarily been limited to laboratory specimens because complexities involved in making these replicas - requiring acetate tape to be dissolved with acetone - are not well suited for a crack inspection tool. More recently developed silicon-based replicas are better suited for use as a crack detection tool. A commercially available silicon-based replica product has been determined to be acceptable for use in SSME hydrogen feedlines. A method has been developed using this product and a scanning electron microscope for analysis, which can find cracks as small as 0.005 inches and other features (e.g., pits, scratches, tool marks, etc.) as small as 0.001 inches. The resolution of this method has been validated with dozens of cracks generated in a laboratory setting and this method has been used to locate 55 cracks (ranging in size from 0.040 inches to 0.004 inches) on space flight hardware. These cracks were removed by polishing away the cracked material and a second round of replicas confirmed the repair.
Document ID
20080013504
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Newman, John A.
(NASA Langley Research Center Hampton, VA, United States)
Smith, Stephen W.
(NASA Langley Research Center Hampton, VA, United States)
Piascik, R. S.
(NASA Langley Research Center Hampton, VA, United States)
Willard, Scott A.
(Lockheed Martin Space Operations Hampton, VA, United States)
Dawicke, David S.
(AS and M, Inc. Hampton, VA, United States)
Date Acquired
August 24, 2013
Publication Date
January 1, 2007
Subject Category
Structural Mechanics
Meeting Information
Meeting: 18th AeroMat Conference and Exposition (AeroMat 2007)
Location: Baltimore, MD
Country: United States
Start Date: June 25, 2007
End Date: June 28, 2007
Funding Number(s)
WBS: WBS 732759.07.09
Distribution Limits
Public
Copyright
Public Use Permitted.
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