In-Situ Monitoring of Strain Distribution of FRP by Rayleigh Scattering-Based Optical Fiber Sensors and Their Applications

Recently composites have been applied to many engineering fields such as automotives and then cost reduction and improvement of efficiency of the manfacturing process has been considered as key technologies in near future. For the purposes, in-situ and internal monitoring of composites during molding process is very effective. Many smart sensors have been devloped for monitoring flow front of impregnated resin, degree of cure, complex stifness and process-induced strain. Amog these sensors, optical fiber sensors are considered to be promising sensors due to easy embedment, multi-functionality and life-time usability. For example, Fresnel-based sensors can measure degree of cure precisely and FBG ( Fiber Bragg Grating) sensors can be used for measuring strain with high accuracy and stability while these sensors have sensing point and cannot be used for measuring distribution. On the other hand, optical fiber distribution sensors can measure strain and temperature distribution along fiber length. B-OTDR (Brillouin Optical Time Domain Reflectometry) was used for measuring strain distribution of composites during molding. However the typical spacing resolution is a few sub-meters and then the application was limitted to large-scale structures.