Detection of edge delamination in CFRP laminates under cyclic loading using small-diameter FBG sensors

Small-diameter FBG sensors were applied for the detection of edge delamination in carbon fiber reinforced plastic (CFRP) quasi-isotropic laminates. Reflection spectra from the embedded fiber Bragg grating (FBG) sensor were measured at various lengths of delamination initiated from the edge of the specimen under cyclic loading. The form of the spectrum changed sensitively as the edge delamination grew. For confirmation of the measured results, the strain distribution in the FBG sensor was calculated by FEM analysis and the spectrum was simulated from the strain distribution theoretically. The change in the form of the measured spectrum was consistent with that of the calculated spectrum. From these results, the spectrum was found to depend on the size and location of the edge delamination. Moreover, the intensity ratio of the two peaks in the spectrum was proposed as an effective indicator for the quantitative evaluation of the edge delamination size.