In 2005 and 2006, NASA Glenn Research Center researchers tested and characterized thermal protection system candidate materials in support of the Lightweight Nonmetallic Thermal Protection Materials Technology Project. Efforts at Glenn included a nondestructive evaluation (NDE) study of six different state-of-the-art ceramic matrix composite and carbon-carbon composite thermal protection system candidate materials (55 specimens total). The materials are applicable to space/hypersonic vehicle heat shields, control surfaces, and leading edges.
A pulsed thermography study was designed and conducted by Glenn researchers to characterize 1- by 4-in. ceramic matrix composite and carbon-carbon specimens in the as-fabricated condition and following exposure to simulated space environments at the NASA Marshall Space Flight Center, which included micrometeoroid object damage, atomic oxygen exposure, or combined radiation effects conditioning. All samples were subsequently exposed to a simulated Earth entry from lunar return in NASA Langley Research Center’s Multiparameter Mission Simulation Facility (MMSF), followed by pulsed thermography and surface and microstructure examination at Glenn. Pulsed thermography is a nondestructive evaluation method that involves the heating of a specimen with a short-duration pulse of energy and monitoring the transient thermal response of the surface of the specimen with an infrared camera (see the sketch). Anomalous subsurface areas can then be identified on the basis of deviations in cooling behavior at the surface.
Pulsed thermography setup. High-intensity flash lamps impart a
short pulse of heat into the specimen. The thermal response to this
input is monitored using an infrared camera and is recorded and processed
using a computer.
The ability to use pulsed thermography to locate and monitor damage and material changes at and beneath the surface of the composites was demonstrated (see the following figure). The collection of thermography data in the as-fabricated condition proved useful in providing baseline condition information and in tracking material changes following environmental exposure. This NDE technique was shown to be particularly well-suited for assessing hidden material damage due to micrometeoroid object damage exposure and MMSF conditioning. Microstructural and chemical characterization of the sample surfaces, and sectioning and microscopy of samples at selected areas where thermography “indications” occurred, were performed to aid in understanding the source of changes in the NDE signals, and in an attempt to reduce the need for destructive evaluation of parts manufactured from these materials. The NDE results are documented and summarized in the NASA Marshall project report (Gubert et al.).
Top: Thermography results for a carbon-carbon composite specimen
in the as-received (undamaged) condition. Center: Thermography image
obtained following simulated micrometeoroid damage. Subsurface damage
is revealed by dark areas. Bottom: Optical image. Subsurface damage
cannot be seen.
Hurwitz, Frances I., et al.: Oxidation Behavior of CMC Candidate Materials for Lightweight Nonmetallic TPS for NASA Exploration Missions. Proceedings of the 2006 National Space and Missile Materials Symposium, Orlando, FL, 2006.
Hurwitz, Frances I., et al.: Microstructural Characterization of Candidate Thermal Protection Materials Following Simulated Space Environments Exposure. 31st Annual Conference on Composite Materials and Structures, Afternoon Jan. 25, Session 1: Hypersonic Materials 4, Daytona Beach, FL, Jan. 22-25, 2007. Available only on DVD from Zimmerman Associates Inc. (ZAI), Arlington, VA.
Martin, Richard E.; Gyekenyesi, Andrew L.; and Shepard, Steven M.: Interpreting the Results of Pulsed Thermography Data. Mater. Eval., vol. 61, no. 5, 2003, pp. 611-616.
Gubert, Michael K., et al.: MSFC-RPT-3486: Effects of Space and Planetary Environments on TPS Materials—Integrated Test Report, pp. 39-45, August 31, 2006. Also Martin, Richard E.; Kiser, J. Douglas; and Hurwitz, Frances I.: Appendix G: Thermography and Post-Exposure Images, pp. 380-458.
Find out more about the research of Glenn’s Optical Instrumentation & NDE Branch: http://www.grc.nasa.gov/WWW/OptInstr/
Cleveland State University contact: Richard E. Martin, 216-433-3684, Richard.E.Martin-1@nasa.govLast updated: December 14, 2007
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