Quantitative evaluation of transverse cracks in carbon fiber reinforced plastic quasi-isotropic laminates with embedded small-diameter fiber Bragg grating sensors

The authors have applied newly developed small-diameter fiber Bragg grating (FBG) sensors, whose cladding is 40 mum in diameter, for the detection of transverse cracks in carbon fiber reinforced plastic (CFRP) laminates. In previous research, the small-diameter FBG sensors were embedded in CFRP cross-ply laminates. When transverse cracks occurred, reflection spectra from the FBG sensors broadened with an increase in the crack density. Thus, the authors showed that small-diameter FBG sensors had the potential to detect the occurrence of cracks. In the present research, this technique is applied to the detection of the transverse crack evolution in CFRP quasi-isotropic laminates, whose laminate configuration is more suitable for practical use. Through the experiment and the theoretical calculation, it was found that the small-diameter FBG sensor could also detect transverse cracks in quasi-isotropic laminates quantitatively.