18 October 2007 Optical fiber distributed sensing structural health monitoring (SHM) strain measurements taken during cryotank Y-joint test article load cycling at liquid helium temperatures
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Proceedings Volume 6770, Fiber Optic Sensors and Applications V; 677003 (2007); doi: 10.1117/12.731605
Event: Optics East, 2007, Boston, MA, United States
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.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Sidney G. Allison, William H. Prosser, David A. Hare, Thomas C. Moore, W. Scott Kenner, "Optical fiber distributed sensing structural health monitoring (SHM) strain measurements taken during cryotank Y-joint test article load cycling at liquid helium temperatures", Proc. SPIE 6770, Fiber Optic Sensors and Applications V, 677003 (18 October 2007); doi: 10.1117/12.731605; http://dx.doi.org/10.1117/12.731605
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KEYWORDS
Fiber Bragg gratings

Cryogenics

Fiber optics sensors

Liquids

Sensors

Structural health monitoring

Helium

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