Detection of transverse cracks in composites by using embedded FBG sensors

摘要

In the present research, fiber Bragg grating (FBG) sensors were applied for the detection of transverse cracks, which cause strain distribution within the gage length, in carbon fiber reinforced plastic (CFRP) cross-ply laminates. An uncoated FBG sensor was embedded in 0 deg ply on the border of 90 deg ply in a CFRP cross-ply laminate. The reflection spectra from the FBG sensor were measured at various tensile stresses. As a results, the reflection spectrum became broad and had some peaks with increase of the transverse crack density int he 90 deg ply. After the crack density was saturated, the spectrum became narrow nad had one large peak again. For confirming that the change in the spectrum form was caused by transverse cracks, the spectra were calculated theoretically. The calculated results reproduced the change in the measured spectrum form very well. These results show that the occurrence of transverse cracks can be detected from the change in the form of the reflection spectrum, and the spectrum width at the half-maximum is a good indicator for the quantitative evaluation of the transverse crack density on real-time.