Comparison of several strain transfer theory calculation methods of the embedded FBG strain sensors

摘要

The fiber Bragg grating (FBG) sensor is broadly accepted as a structural health monitoring device by either embedding into or bonding onto the structures. The measuring accuracy of FBG strain sensor is mainly determined by the physical and mechanical performance of bare fiber, protective coating, adhesive layer and host material; namely the interface strain transfer characteristics between these layers. In general, the signal extracted from the embedded FBG sensor should reflect the straining condition of the host structure. However, due to the existence of an adhesive layer and protective layer and protective coating, part of the energy would convert into shear deformation. Therefore, the mechanical properties of these materials would affect the resultant strain measured by embedding a FBG sensor into the structure. Some studies showed the theoretical model to evaluate the differential strain between the bare fiber and host material of the embedded FBG sensor. In this paper, finite element method (FEM) has been introduced to calculate inner strains of each layer with FBG strain sensors embedded in host material. Based on the experimental and calculation calculational results, more accurate theoretical model is selected.