The Response of Embedded NIR (830 nm) Fiber Bragg Grating Sensors in Glass Fiber Composites under Fatigue Loading

The fabrication and use of fiber Bragg grating (FBG) sensors, which operates in near infrared region (Bragg wavelength lambda(B) = 830 nm) to monitor the damage accumulation in composite is reported. The spectra similar to 830 nm of the embedded FBG sensor in 0 degrees/90 degrees woven cloth/vinyl ester composite were distorted and broadened due to fatigue loading, as expected. These distortions in FBG spectra indicate asymmetric and nonuniform strain distributions along the grating length of the FBG sensors due to the accumulation of damage during fatigue loading regimes. This information is useful for formulating a fundamental relationship between FBG spectral changes and the damage accumulation of composite structures. The results demonstrate that the sensitivity and durability of the embedded FBG sensors fabricated by conventional writing techniques at 830 nm range and monitored using inexpensive Si-based source and arrays were excellent for health monitoring of composite structures.