Investigation of multifunctional fiber optic sensor in smart composite

Abstract

In the autoclave curing of laminates, the viscosity of the resin is very important for controlling the fabrication of composite structures. In this paper it is proposed to measure changes of viscosity of composite resin using fiber optic microbend attenuation. Optical fibers are selected and processed to increase sensitivities. Experimental viscosity measure- ments for different layup conditions have been made, and the results are compared with those of dielectric measurement. It is found that fiber optic attenuation is sensitive to composite cure monitoring in an auto- clave with good reliability, and can indicate the point of lowest viscosity, the gel point, and the end 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 the cure process. Embedded optical fibers that can be used for cure monitoring and that maintain optical waveguide performance have been developed for use in two sorts of vibration sen- sors (SMS-A and SMS-B) based on fiber optic vibration-mode statistics. In an experiment using an SMS-A sensor, the sensor precision is evalu- ated and shows that the measurement results are accurate and credible. A method of evaluating mechanical characteristics by vibration measure- ment is also described. In an experiment using an SMS-B sensor, mea- surements of vibration frequencies and amplitudes were made, and the factors that influence their sensitivity and measurement range are dis- cussed. © 2001 Society of Photo-Optical Instrumentation Engineers.