27 June 2002 Measurement of local bending moment using embedded optical fiber Bragg grating sensors
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Fiber Bragg gratings have demonstrated great potential as sensing elements for the structural health monitoring (SHM) of composites. However, the complexity of stress and strain fields due to one or multiple damages makes the health-monitoring problem extremely difficult and sensitive to errors. Current approaches consider only the Bragg grating averaged axial strain as input to the health-monitoring algorithm. This paper presents a strategy to improve SHM information. In previous experiments, Bragg grating sensors embedded to measure the strain field near a crack demonstrated significant loss in their reflected spectrum at high strain. This loss was not a constant but a function of wavelength and is shown to be due to bending. The effect of shear loading is shown to be negligible. In order to demonstrate the technique an axially loaded unidirectional composite with a transverse crack is considered. The axial stress distribution is calculated using a modified shear lag theory suitable for multiple fibers and cracks. The bending stress at the crack tip is calculated using linear elastic fracture mechanics and a FEM model. From the calculated stress field a grating response simulation is performed taking into account the local bending of the fiber.
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Mohanraj Prabhugoud, Mohanraj Prabhugoud, Kara J. Peters, Kara J. Peters, } "Measurement of local bending moment using embedded optical fiber Bragg grating sensors", Proc. SPIE 4694, Smart Structures and Materials 2002: Smart Sensor Technology and Measurement Systems, (27 June 2002); doi: 10.1117/12.472631; https://doi.org/10.1117/12.472631

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