Response of embedded fibre Bragg gratings: strain transfer effects

This paper presents the transverse response of fibre Bragg grating sensors embedded in small cross-ply composite laminates. Since the optical fibre (isotropic) and the host material (anisotropic) have different material properties, strain in both materials will not be equal when load is applied. Therefore, the strain transfer from host material to the embedded sensor (optical fibre) has been determined using FE-simulations. Composite laminates with embedded optical fibre sensors were submitted to transversal stress. This load case induces high birefringence effects in the core of the optical fibre by which, using the calculated strain transfer coefficients together with multi-axial strain formulations, the authors were able to measure the total strain field of a carbon fibre reinforced plastic specimen.