Influences of adhesive properties on strain measurement results of rayleigh backscattering based fibre optic sensors

Distributed Fibre Optic Sensors (DFOS) for structural monitoring purposes feature good performance in harsh environments, considerable versatility, nearly no impact on the structure's mass, relative low-cost, small dimensions and the option to integrate it into existing as well as new structures. [1] Furthermore, through the use of DFOS it is possible to continuously measure environmental and structural key parameters, e.g. multiple temperature and strain values, using one single optical fibre, thus creating a truly distributed sensor. This work investigates the behaviour of a Rayleigh backscattering based measurement system with respect to the adhesive used for application of the fibre and the geometrical properties of the bonding joint. Experimental results are presented for the influence of different adhesives and application methods, as well as different bonding lengths of the fibre. Data from the fibre optic sensor are compared to those acquired using standard strain gauges to be able to detect differences in the strain field caused by the type or geometry of the adhesive layer. The results of these measurements are then complemented with results of FEM simulations. This encompasses numerical research on varying geometry parameters of the bonding joint. Varying bonding length, thickness and stiffness values have been considered in the FE analysis. The influence of the previous parameters on the strain transfer and the edge effects is shown using data from FE analyses as well as from experiments.