Chapter 5 : FBG stress sensors

FBGs in low-birefringent optical fibers are very efficient axial stress sensors. Within the collaboration with the Laboratoire de mécanique appliquée et d'analyse de fiabilité (LMAF), FBGs fabricated in our institute have been used with success as strain gauges. A promising preliminary experiment on the reconstruction by OLCR and layer-peeling of non-homogeneous axial strain fields is developed in section 5.1. Other applications of FBGs for axial strain measurements, not detailed hereafter, include : 1) studies on bridging cracks in composites in collaboration with Michel Studer [5-1 to 5-3], 2) studies on the deformation behavior of composite laminates in collaboration with Federico Bosia [5-4 to 5-6] and 3) studies on the characterization of FBGs in non-homogeneous axial stress fields by simulation of the spectral intensity response in collaboration with Prof. Kara Peters and Philip Pattis [5-9, 5-10].

The behavior of FBGs subjected to transversal stress fields has been analyzed for gratings written in low-birefringent and polarization maintaining fibers. A diametric load experiment is presented in section 5.2 and applications in the measurement of transversal strain fields in composites have also been studied [5-7, 5-8].