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Development of SHM System Using Multiple FBG Sensors for Solid Rocket Motor Composite Chamber



A structural health monitoring system using four fiber Bragg grating sensors (FBG sensors) was developed for solid rocket motor composite chambers. The system was designed to measure a large and fast strain change and to measure acoustic emissions (AE) simultaneously. The strain up to 1% and up to 100 kHz was considered. The system possesses two light sources; a newly developed fourband fiber ring laser and a broadband light source. Using the four-band fiber ring laser, the system can measure strain changes and AE simultaneously. Using the broadband light source, the system can measure high-speed strain changes. The strain sensitivities of FBG sensors obtained from the four-band fiber ring laser system agreed well with those obtained from a broadband light source system. A CFRP beam-bending test was conducted to confirm the possibility of simultaneous measurement of both strain and AE signals from a single FBG sensor. A strain gage and a piezoelectric AE sensor were used for reference. In the test, it was confirmed the strain change up to almost 1% was measured from the developed system. AE detection by an FBG sensor and a piezoelectric AE sensor, however, do have slight differences. The developed system will be applied to composite structures in aerospace engineering fields, such as Epsilon Launch Vehicle, which is under development by the Japan Aerospace Exploration Agency (JAXA).

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