Design of an optical fibre sensor patch for longitudinal strain measurement in structures

The purpose of this study is to design a composite sensor plate, based on a FBG sensor, to be used as alternative to the conventional electric extensometers for structural health monitoring applications. Two different cases are studied: composite patches made from carbon and glass woven reinforcement. Special care is devoted to the embedding process of the optical fibre sensor in the composite plate in order to avoid significant alteration of the optical power spectrum of the light reflected back by the fibre Bragg grating. The strain response of the composite sensor patch to axial loading is compared to electrical strain gage's. A three-dimensional finite element analysis is also proposed to understand the relation between the strain measured by the FBG sensor and the strain imposed to a plate and the consequence, of the application of such composite sensor plate, on the behaviour of a specimen submitted to tensile stress.