This paper presents an experimental study into the static strength and fatigue durability of particular Bragg grating (FBG) optical fibre sensors. The strength and fatigue properties of the sensors were evaluated when externally mounted to carbon fibre-epoxy substrates representative of aircraft composite structures. The results show large differences in the ultimate tensile strength and failure strain between sensors, which is due to randomly sized surface flaws introduced in the optical fibres during Bragg grating manufacture, possibly by chemical stripping, hydrogen loading, moisture ingress and handling. Fatigue experiments were performed on the sensors under cyclic tension over a wide range of strain levels. It was found that above a fatigue strain threshold, the quality of the Bragg grating signal degraded with increasing number of stress cycles until eventually the sensor broke. The deterioration of the Bragg grating signal was due to light-scattering from cracks formed in the fibre by fatigue loading. The fatigue life (S-N) curve and parameters affecting the fatigue performance of the sensor are identified in the paper. The study reveals that the fatigue endurance strain limit (106 cycles) of these sensors is -3500 my epsilon, which is considered adequate for most aerospace structural applications.
Tensile fatigue performance of surface mounted Bragg grating optical fibres for use in structural health monitoring
2008
8 Seiten, 7 Quellen
Conference paper
English
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