Curing monitoring of cross-ply and quasi-isotropic-ply carbon fiber/epoxy composite material with metal-coated fiber Bragg grating sensors

Abstract

In this study, two metal-coated fiber Bragg grating (MCFBG) sensors and one bare FBG sensor were embedded into a cross-ply and a quasi-isotropic-ply laminated composite material to monitor the property changes of the material during the curing process. Thereafter, the embedded metal-coated and bare FBG were used to calculate the residual curing strain of the composite by monitoring the spectrum variations and to make residual strain comparisons in the various laminated locations between cross-ply laminates and quasi-isotropic-ply laminates. This is a subject of research that has not yet been investigated. The spectra of the metal-coated and bare FBG sensors shift and become deformed during the curing process. This phenomenon is caused by residual strain during composite curing. According to the experimental results, the residual axial strain of the cross-ply laminate-layer with a ZrN-coated sensor was reduced by 2.742% compared to that of the cross-ply laminate-layer with a bare FBG sensor, while that of the cross-ply laminate-layer with a CrN-coated sensor was reduced by 3.624%. The residual axial strain of the quasi-isotropic-ply laminate-layer with a ZrN-coated sensor was reduced by 7.553% compared to that of the quasi-isotropic-ply laminate-layer with the bare FBG sensor, while that of the quasi-isotropic-ply laminate-layer with a CrN-coated sensor was reduced by 8.025%.Therefore, the reduced axial residual strain is more pronounced in the quasi-isotropic-ply laminates than in the cross-ply laminates. We also found that the bare FBG sensors without a metal coating have a greater degree of curvature than the MCFBG sensors, which have a metal coating. The metal coating on the MCFBG sensor has a good protective effect that can extend the service life of the sensor. In summary, the effective performance of an FBG sensor coated with nitride thin films has been demonstrated in this study.