Fibre optics health monitoring for aeronautical applications

The detection of stress/strain field in structural components represents one of the cornerstones of continuous mechanics analysis of materials and structures. In particular, this paper presents some of the most remarkable aspects of aeronautical structures monitoring techniques through fibre optics (FO) sensors; given their capability to convert local or distributed strains into optical signal and to transmit it remotely, optical fibres represent a powerful detection tool which can be integrated in complex structures. Firstly, some basic technological concerns to be tackled in view of sensors integration are considered, e.g. trade-off process between bonding and embedding techniques, co-bonding or co-curing, inter- or intra-laminar embedment, compatibility between host material and optical fibres, degree of invasivity and interface analysis, bending sensitivity, use of quick-packs and connectors to guarantee sensors integrity and functionality. Then, general concerns to be faced during the design process of sensors networks for strain sensing, health- and process-monitoring are analysed (e.g. distributed, localized and co-located sensors, hot-spot identification, signal management, multiplexing, attenuation). Moreover, a number of issues are addressed for a reliable conversion of optical signal into mechanical strain field. In particular, theoretical and experimental techniques are presented, devoted to thermal/mechanical signals decoupling. Finally, the use of fibre Bragg’s grating sensors and chirped arrays are compared in view of solving the problem of reconstructing the stress/strain field on the basis of spectral signals provided by FO sensors.