Abstract
In general, the reflective signal of fiber Bragg grating (FBG) sensors has the shape of a single sharp peak. This signal shape can be broadened or split by non-axisymmetric stress or strain gradient applied to the grating region. Because of this signal distortion, researches have reported the difficulties in using embedded FBG sensors for the strain measurement of the composite structures. In this study, the small diameter FBG sensor (40 μm in diameter) which was recently developed for embedded applications was tested in a quasi-static indentation. Both cylindrical and spherical indentors are used to give different stress conditions to the sensor embedded in a thin composite plate. A normal diameter FBG sensor (125 μm in diameter) was also tested in the same conditions for comparison. The results of indentation tests using the spherical indentor were analyzed using simplified finite element models to estimate stress distributions in each FBG sensor. The difference in the spectral behaviors of two FBG sensors was explained using finite element analysis.
