Effect of thermal residual stress on fiber Bragg grating sensors embedded in T-stiffened panels

To monitor the strains of the composite T-stiffened panels during its curing and compression after impact, the fiber Bragg grating(FBG) sensors were embedded in the triangle area of the composite T-stiffened panels(structure non-interference region). The reflection spectra obtained from the uncoated FBG sensors and the FBG sensors coated with UV-cured resin were compared, and the effect of thermal residual stress on the reflection spectrum was studied. It was indicated that the full width at half maximum(FWHM) value of the coated FBG sensor almost unchanged during the curing, and the thermal residual stress upon the reflection spectrum can be attenuated by coating UV-cured resin on the FBG sensors. Furthermore, the strain measured by the coated FBG sensor is correspondence to the results of the strain gauge on the composites surface. The validity of the strain measured by FBG sensors was verified during the curing and the compression after impact.