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27 June 2002 Crack identification in CFRP laminates using small-diameter FBG sensors
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The authors have applied newly developed small-diameter fiber Bragg grating (FBG) sensors, whose cladding is 40 micrometers in diameter, for the detection of transverse cracks in carbon fiber reinforced plastic (CFRP) laminates. In the previous research, the small-diameter FBG sensors were embedded in CFRP cross-ply laminates. When the transverse cracks occurred, reflection spectra from the FBG sensors became broad with an increase in the crack density. Thus, the authors revealed that the small-diameter FBG sensors have a potential to detect the occurrence of the cracks. In the present research, this technique was applied to the detection of the cracks in CFRP quasi-isotropic laminates, whose laminate configuration was more suitable for the practical use. Through the experiment and the theoretical calculation, it was found that the small-diameter FBG sensor could also detect cracks in the quasi-isotropic laminates. Furthermore, the identification of the crack locations was attempted using an inverse scattering algorithm. The profiles of the grating period and the average refractive index were inversed from a complex reflection spectrum with this algorithm. From the profiles, the cracks could be identified, because the positions of the peaks in the profiles corresponded to the locations of the cracks.
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Tadahito Mizutani, Yoji Okabe, and Nobuo Takeda "Crack identification in CFRP laminates using small-diameter FBG sensors", Proc. SPIE 4694, Smart Structures and Materials 2002: Smart Sensor Technology and Measurement Systems, (27 June 2002);

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