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Proceedings Paper

Optical fiber distributed sensing structural health monitoring (SHM) strain measurements taken during cryotank Y-joint test article load cycling at liquid helium temperatures
Author(s): Sidney G. Allison; William H. Prosser; David A. Hare; Thomas C. Moore; W. Scott Kenner
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Paper Abstract

This paper outlines cryogenic Y-joint testing at Langley Research Center (LaRC) to validate the performance of optical fiber Bragg grating strain sensors for measuring strain at liquid helium temperature (-240°C). This testing also verified survivability of fiber sensors after experiencing 10 thermal cool-down, warm-up cycles and 400 limit load cycles. Graphite composite skins bonded to a honeycomb substrate in a sandwich configuration comprised the Y-joint specimens. To enable SHM of composite cryotanks for consideration to future spacecraft, a light-weight, durable monitoring technology is needed. The fiber optic distributed Bragg grating strain sensing system developed at LaRC is a viable substitute for conventional strain gauges which are not practical for SHM. This distributed sensing technology uses an Optical Frequency Domain Reflectometer (OFDR). This measurement approach has the advantage that it can measure hundreds of Bragg grating sensors per fiber and the sensors are all written at one frequency, greatly simplifying fiber manufacturing. Fiber optic strain measurements compared well to conventional strain gauge measurements obtained during these tests. These results demonstrated a high potential for a successful implementation of a SHM system incorporating LaRC's fiber optic sensing system on the composite cryotank and other future cryogenic applications.

Paper Details

Date Published: 18 October 2007
PDF: 12 pages
Proc. SPIE 6770, Fiber Optic Sensors and Applications V, 677003 (18 October 2007); doi: 10.1117/12.731605
Show Author Affiliations
Sidney G. Allison, NASA Langley Research Ctr. (United States)
William H. Prosser, NASA Langley Research Ctr. (United States)
David A. Hare, NASA Langley Research Ctr. (United States)
Thomas C. Moore, NASA Langley Research Ctr. (United States)
W. Scott Kenner, NASA Langley Research Ctr. (United States)

Published in SPIE Proceedings Vol. 6770:
Fiber Optic Sensors and Applications V
Eric Udd, Editor(s)

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