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Development and experimental verification of a structural health monitoring system for composite beams with embedded fibre bragg grating sensors

Değerliyurt, Boray
Structural Health Monitoring (SHM) is a discipline of development and application of monitoring and detecting adverse changes and damage in a structure in operation. This study explains development of a SHM system of composite beams with embedded Fibre Bragg Grating (FBG) sensors and its verification through experiments. There are considerations that require attention during manufacturing of composite specimens with embedded sensors. During manufacturing, protective teflon tubes are added to the ingress and egress regions to prevent fibre-optic wire breaking due to stress concentrations. Moreover, as interrogator connectors at the tip of fibre optic wires cannot stand high autoclave temperatures, they are cut and joined back to fibre optic wires again after manufacturing through fusion splicer device. There are three types of experiments performed for the verification; tension, vibration and fatigue torsion. The verification is done through comparing embedded FBG sensors data to that of corresponding surface mounted ones. To establish strain relation between embedded and surface mounted FBG sensors, strain distributions over the vi cross-section of the beam are calculated by finite element analyses (FEA) for each experiment. When embedded sensors satisfy the obtained strain distributions in each experiment, the developed SHM system with embedded FBG sensors will be proved to work properly. Furthermore, data of the surface mounted FBG sensor and the strain gauge are also compared in tension experiments. They both satisfy strain distributions calculated from FEA. Noise signals of both sensors are extracted and compared in both time and frequency domains. As a result of the experiments, strain data of the embedded FBG sensors satisfy necessary strain conditions calculated from FEA for each experiment. In free vibration experiment, embedded sensors successfully capture the resonance frequencies corresponding to the first two out-of-plane bending modes of the composite specimen, values of which are the same as the ones captured by the surface mounted FBG’s. Moreover, FBG sensors are observed to have better performance than strain gauges in terms of noise content. Results of three types of experiments verify that the SHM system with embedded FBG sensors works properly. Therefore, it is shown that embedded sensor technology can successfully be applied on composite specimens.