Turning aeronautical brackets into smart monitoring devices: integration of sensors and load identification algorithms

In this work, a metallic additive manufactured bracket sensorized with optical fibres was developed with the capability of identifying the applied load magnitude and orientation. Additive manufacturing technology was exploited for the integration of sensors, exploring the possibility of producing internal and external channels for the housing of the optical fibres endowed with fibre Bragg gratings for strain and temperature sensing. The strain transfer between the metallic element and the sensors was studied numerically and experimentally, embedding the fibres into composite patches, co-bonded to the metallic element. A flap track support was selected as application scenario, which was printed in titanium alloy by selective laser melting. A two-step load identification method based on strain sensing was devised. The first model-based step adopts a notional finite element model for the extraction of the influence functions linking applied loads and local strains. The second step is a data-based correction procedure, which involves a limited number of calibration tests on the physical element and the identification of correction factors for the influence functions by means of a genetic algorithm. The description of the algorithm and a first validation by means of virtual tests is presented in detail. A demonstrator of the sensorized bracket was manufactured, proving experimentally the possibility of identifying the loads in conditions different from those used for the data-based correction. Overall, the study provides the methods for designing multifunctional structural connections that integrates structural and load monitoring roles and can be assembled into structures without modifying the conventional manufacturing procedures.