Optical fiber sensors (OFS) have attracted considerable interests for health monitoring of the structures in recent years due to their many advantages such as embedding in materials, real-time strain monitoring and non-perturbation by electro-magnetic noises. In this paper, longitudinal strains ( x) of the core and the skin layers in glass fiber reinforced plastic (GFRP) cross-ply composite laminates have been measured using the embedded optical fiber sensors of absolute extrinsic Fabry-Perot interferometer (A-EFPI). Foil-type strain gauges bonded on both the upper and lower surfaces of a specimen were used for comparison of the surface strains. It was shown that values of x in the interior of the skin layer and the core layer measured by embedded A-EFPI sensor were significantly higher than those of the specimen surface measured by strain gauges. Experimental results agreed well with those from finite element analysis based on uniform stress model. Also, transmission optical microscopy was used to investigate the damage behavior around the A-EFPI sensor. Large strains in the core layer led to the occurrence of many transverse cracks which drastically reduced strains at the failure of optical fiber sensor embedded in the core layer.
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