Feasibility study of FBG-based sensors for prognostics in aerospace applications

In recent years, aerospace systems have undergone a huge technical-scientific impulse, evolving new high-performance intelligent solutions able to perform diagnostic and prognostic functions autonomously. In this scenario, an important role is certainly played by the new types of sensors combining high performance (in terms of sensibility, accuracy, and reliability) with a marked resilience to external disturbances (e.g. EM noise or electrostatic discharges) and other environmental factors. Fiber Bragg Gratings (FBGs)sensors, suitable for measuring various engineering parameters in both static and dynamic modes, meet all these requirements; in aerospace, they could replace several traditional sensors, not only in structural monitoring but also in a much wider range of system applications including the diagnostic and prognostic of mechatronic devices. In this paper, the authors propose the first results of their investigation about the use of optical sensors for Electromechanical (EMA) and Electrohydrostatic Actuators (EHA). FBGs allow determination of aerodynamic hinge loads and minimally invasive measurements of local temperatures: the firsts are needed for in-flight model-based prognostics, whereas the detection of local heating allows to early infer an incipient partial short circuit of EM motor, a progressive power electronics failure or abnormal friction dissipation e.g. at bearing level. In order to assess the capabilities of optical sensors, evaluating different installation techniques and defining suitable configurations for the aforementioned mechatronic systems, a dedicated test bench has been developed and used for calibrating FBGs, analyzing their behaviour in different conditions of strain and temperature and conceiving a proper thermo-mechanical compensation strategy.