A new method for measuring non-uniform strain fields using fibre Bragg grating sensors is proposed and demonstrated. The method is based on the measurement of the complex impulse response of the grating by optical low coherence reflectometry and the retrieval of the local Bragg wavelength by the layer-peeling technique. This method is applied to measurements of non-uniform strain distributions generated in a double-edge-notched thin plate made of epoxy, where a 24.1 mm long grating is embedded at the specimen centre along the loading direction and orthogonally to the notches. The axial strain distribution along the grating is determined with an absolute error of 30 µε. The results are compared with finite element simulations and a good agreement is observed.
This paper describes the production of an adaptive composite by embedding thin pre-strained shape memory alloy actuators into a Kevlar-epoxy host material. In order to combine the activation and sensing capabilities, fibre Bragg grating sensors are also embedded into the specimens, and the strain measured in situ during activation. The effect of manufacturing conditions, and hence of the initial stress state in the composite before activation, on the magnitude of the measured strains is discussed. The results of stress and strain simulations are compared with experimental data, and guidelines are provided for the optimization of the composite. Finally, a pilot experiment is carried out to provide an example of how a strain-stabilizing feedback mechanism can be implemented in the smart structure.
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