Investigation of multifunctional fiber optic sensor in smart composite

In the autoclave curing of laminates, the viscosity of the resin is very im portant for controlling the fabrication of composite structures. In this pa per it is proposed to measure changes of viscosity of composite resin using fiber optic microbend attenuation. Optical fibers are selected and process ed to increase sensitivities. Experimental viscosity measurements for diffe rent layup conditions have been made, and the results are compared with tho se of dielectric measurement. It is found that fiber optic attenuation is s ensitive to composite cure monitoring in an autoclave with good reliability , and can indicate the point of lowest viscosity, the gel point, and the en d point of the cure. The sensitivity is found to be related to the crossing angle between optical fiber and reinforcing fiber and to the pressure in t he cure process. Embedded optical fibers that can be used for cure monitori ng and that maintain optical waveguide performance have been developed for use in two sorts of vibration sensors (SMS-A and SMS-B) based on fiber opti c vibration-mode statistics. In an experiment using an SMS-A sensor, the se nsor precision is evaluated and shows that the measurement results are accu rate and credible. A method of evaluating mechanical characteristics by vib ration measurement is also described. In an experiment using an SMS-B senso r, measurements of vibration frequencies and amplitudes were made, and the factors that influence their sensitivity and measurement range are discusse d. (C) 2001 Society of Photo-Optical Instrumentation Engineers.