DETECTION OF CRACKS IN FRP BY USING EMBEDDED PLASTIC OPTICAL FIBER

Abstract

Plastic optical fiber is a multi-mode optical fiber and used for short distance communication, illumination, etc. Plastic optical fibers can be also used as a damage sensor by measuring optical power loss. Plastic optical fibers are much cheaper and easier to connect than silica fibers, and suitable to be embedded in FRP because of the similarity of its elasticity and coefficients of thermal expansion. In this work, plastic optical fibers were embedded in three types of GFRP specimens including unidirectional and cross-ply laminates. The relations among the optical power, the strain and the number of cracks were studied. Cracks in GFRP lamintes were observed by a video microscope under tensile load. As the strain increased, the optical power decreased linearly before the initiation of cracks and nonlinearly after that. The optical power loss by a single crack was simulated by using a three-dimensional ray tracing model and the results were compared with the experimental results. Then, it was concluded that the nonlinearity of curve of the optical power loss was affected by the cracks and the plastic optical fiber has much potential to be used as a crack-detecting sensor for smart composites.