Assessment of the strain monitoring reliability of fiber Bragg grating sensor (FBGs) in advanced composite structures

Fiberoptic Bragg grating sensors were embedded in composite structures in order to be used as the detection system for structural health monitoring purposes. Firstly, optical fibers had been embedded in several locations in between the layers of composite material and for the typical tensile testing coupon configuration. It has been shown experimentally and with finite element analysis that embedding the optical fiber out of the neutral axis of the coupon, downgrades significantly the composite’s ultimate tensile strength. Secondly, a composite patch with embedded FBG has been used to restore a typical damage case on aluminum structure currently applied on advanced ‘aging’ vehicles. Data values taken from the FBG system during the experimental tension tests of the composite structures were calculated to axial strain values with the aid of an interrogator. Theoretical axial strain values of the composite patch had been calculated by exploiting a newly-developed finite element model. Discussion has been made on the correlation between experimental and theoretical results for the verification of sensing sensitivity and accuracy.