Cure monitoring and mechanical properties measurement of carbon fibre-reinforced plastics laminate using embedded fibre Bragg grating sensors

Abstract

Two fibre Bragg grating sensors FBG1 and FBG2 are, respectively, embedded in the carbon fibre-reinforced plastics laminate with the ply schedule of [0/90/452/02/−452]s. The two fibre Bragg gratings are used continuously to monitor the internal temperature and strain of carbon fibre-reinforced plastics laminate in its entire life cycle. During the curing process, the internal temperature and strain of carbon fibre-reinforced plastics laminate are recorded, and the absolute internal thermal strains through temperature compensation are obtained. After complete cooling, the residual strains in different layers are also obtained; they are 88 and −7 με with FBG1 and FBG2, respectively. In order to investigate the internal strain during mechanism loading, a tensile test and three-points bending test are conducted. Coefficients between wavelength shift and tensile force are 0·165 and 0·172 pm N−1 with FBG1 and FBG2, respectively. The coefficient between wavelength shift and bending force is −1·403 pm N−1 with FBG2. It is shown that the fibre Bragg gratings could excellently respond to the tension and bend behaviour in service life. The internal state of carbon fibre-reinforced plastics laminate is successfully monitored throughout its entire life, verifying the effectiveness of life cycle monitoring by fibre Bragg grating sensor for highly reliable composite structures.