Progettazione e realizzazione di una struttura dinamometrica in materiale composito basata su sensori a fibra ottica

The fiber optic sensors (FBGS) have been recently introduced: they present a photo-record grating on the fiber itself, which allows the reflection of a certain wavelength of the light spectrum entered. The applied deformation is estimated based on changes of the reflected wavelength. One of the possible applications that has prompted us to study this type of sensors is the ability to create dynamometric structures based on carbon fiber: these kinds of structures are lightweight, strong and can be used, for example, in the wind tunnel where these characteristics are fundamental. The metrological characteristics of FBGS have been tested and compared to strain gages ones, which represent the actual reference measurement systems. The most expensive FBGS enable on the market have shown to offer metrological performances comparable to electrical strain gages, both in terms of static and dynamic behaviour. Otherwise low-cost FBGS are expected to be characterized by worse performances. It was decided to integrate the measurement system directly into a composite material, having achieved good results during the static and dynamic tests. We made carbon fiber specimens with FBGS integrated in them. The results were surprising: the integration of ``nude'' fiber optic sensor did not cause damage or deterioration in the quality of measurement, the background noise was maintained at baseline levels and response to dynamic stress was absolutely comparable to that offered by electrical strain gauges. The various solutions to compensate for thermal effects have offered several points for analysis and the basis for a future use of these sensors for static or semi-static tests. The possibility of integration of FBG sensors in a material that provides these features opens up new frontiers: it is possible to gain advantage in the construction of dynamometers for use in wind tunnel, characterized by high stiffness combined with limited weights, or even create adhesive patches to be applied to water craft to monitor the deformations.