Development of simultaneous measurement system for strain and AE using FBG sensors (for structural health monitoring of solid rocket motor composite chambers)

A structural health monitoring system using multiple fiber Bragg grating sensors (FBG sensors) was developed. The system was designed to measure a large and a fast strain change and also to measure acoustic emissions ( AE ) simultaneously. The strain up to 1% and up to 100 kHz was considered. A multiple fiber ring laser was adopted as a light source, which consists of a multiple erbium-doped fiber amplifier (EDFA), an optical circulator, optical couplers and FBG sensors. Multiple fiber ring lasing wavelengths depended on strains loaded to FBG sensors. A CFRP beam bending test was carried out to confirm the possibility of simultaneous measurement of both strain and AE signals from a single FBG sensor. In the test, signals from a conventional electric resistive strain gage and a piezo-electric AE sensor were revealed equivalent to those from the FBG sensor. The system will be applied to development of composite structures in aerospace field such as Epsilon Launch Vehicle.