Robust in-space repair technologies are critically needed for the safe operation of the space shuttle as well as the repair and refurbishment of the thermal protection system structures of Crew Exploration Vehicles (CEV). Glenn Refractory Adhesive for Bonding and Exterior Repair (GRABER) was developed at the NASA Glenn Research Center for the repair of reinforced carbon/carbon (RCC) composite thermal protection system structures. The GRABER material has shown multiuse capability for the in-space repair of small cracks and as an adhesive and sealant for RCC leading-edge material. It is a refractory adhesive paste with desired ceramic fillers in a polymer/phenolic resin matrix with appropriate additives such as surfactants. The paste, which is applied to the damaged or cracked area of the RCC composite components with a caulking gun, cures at 100 to 120 °C and transforms into a high-temperature ceramic during reentry conditions.
RCC specimens. (a) Pretest crack-repaired RCC specimen. (b) Arcjet testing, front view. (c) Arcjet testing, side view. (d) Post-test, front-side macrograph. (e) Post-test, back-side macrograph.
GRABER-based materials have multifunctionality and versatility for a wide variety of repair applications. This material was developed primarily to repair small cracks and coating delaminations. For the evaluation of the plasma resistance of this material system, cracks were introduced in RCC specimens by machining slots. These slots (0.035-in. and 1/16-in. wide and 1.5-in. long) were filled with GRABER-based repair compounds and tested in arcjet facilities at the NASA Johnson Space Center and the NASA Ames Research Center for approximately 15 min. All six samples survived the tests without any burn through. The preceding photographs show the pretest crack-repaired RCC specimen, views during arcjet testing, and post-test front-side and back-side macrographs. The GRABER-based repair materials stop the plasma flow through the specimen and prevent any damage. It is important to point out that unrepaired RCC specimens with similar damage had significant burn through because of the plasma oxidation of the RCC, and the small-crack region became a large hole, leading to catastrophic damage.
As an adhesive and sealant in the patch/plug concept, GRABER has performed exceptionally well in plasma torch and arcjet testing in simulated atmospheric reentry environments. The following photograph shows a plug-repaired article where GRABER was used as the sealant. This specimen survived arcjet testing under simulated reentry conditions. GRABER materials also are being used to prepare adhesive patches and flexible ceramic prepregs that use different types of fabrics to repair large areas of damage. The fabric prepregs based on this material system have been used to make ceramic matrix composites and functional coatings and to repair carbon/carbon composites for a wide variety of ground-based applications. Further development and testing efforts are underway to optimize GRABER’s properties and extend the application temperature.
RCC specimen plug-repaired using GRABER 5A as the sealant, shown after arcjet testing.
The GRABER technology was given a 2005 R&D 100 Award. This technology also received honorable mention in Northern Ohio Live Magazine’s 25th Awards of Achievement in the Science and Technology Category.
Find out more about this research:
Glenn innovations receive R&D 100 Awards:
http://www.nasa.gov/centers/glenn/news/pressrel/2005/05-036_R%26D_100_Awards.html
R&D Magazine article about the award:
http://www.rdmag.com/ShowPR.aspx?PUBCODE=014&ACCT=1400000100&ISSUE=0509&RELTYPE=R100&PRODCODE=00000000&PI (external site)
Glenn contact:
Dr. Andrew J. Eckel, 216-433-8185, Andrew.J.Eckel@nasa.gov
QSS Group, Inc., contact:
Dr. Mrityunjay Singh, 216-433-8883, Mrityunjay.Singh@nasa.gov
Authors:
Dr. Mrityunjay Singh and Tarah P. Shpargel
Headquarters program office:
Space Operations
Programs/Projects:
RTF
Special recognition:
2005 R&D 100 Award; Honorable mention in the Science and Technology Category for Northern Ohio Live Magazine’s 25th Awards of Achievement
Last updated: October 16, 2006
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