FOSAS

Fiber Optic Sensors Application for Structural Health Monitoring

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 Obiettivo del progetto (Objective)

'The proposal is addressed to the exploitation of fiber optic based sensor for structural health monitoring of aeronautic structures and materials. The activity plan is organized in three tasks, according to the call description. The first activity will be focused on preliminary research on the use of Fiber Optic Bragg Grating (FOBG) sensors for the strain evaluation during a fatigue test on metallic samples in corrosive environment, with the aim to define and characterize a new experimental methodology capable to provide an innovative tool for the prediction of corrosion initiation. The second activity is addressed to the demonstration of a new approach for the realization and test of an apparatus for FOBG sensors interrogation. The task is motivated by the need to identify a robust and reliable instrumentation for flight test campaign. Starting from results of previous experimental campaign carried out together with Alenia, the actions to develop are devoted to the identification of a new class of commercial devices and/or systems for the integration of a novel instrumentation which should be qualified for flight test campaign and, at the same time, must provide higher performances than conventional equipments. The third research activity will be aimed to the development of a distributed strain and temperature sensing system based on standard optical fibers employment. The scattering effects (Raman, Brillouin, Rayleigh…) on the basis of this new technique will be analyzed and prototypal and commercial solution, already certified for laboratory application, will be evaluated. The distributed technique will be tested during ground test campaign, with the aim to reach performances comparable to these typical of FOBG based discrete sensing systems. In conclusion, the proposal is aimed to provide theoretical and experimental support for the exploitation of new technologies for the realization of smart materials and structures.'

Introduzione (Teaser)

Aircraft safety requirements are among the most stringent around. Advanced fibre optic structural health monitoring (SHM) technologies will support aircraft safety while significantly reducing maintenance and operating costs.

Descrizione progetto (Article)

The use of fibre optic sensors for SHM has increased rapidly in recent years to obtain real-time data on stress or strain in structures such as buildings, bridges and pipelines. Adapting the best of these technologies for flight worthiness and aircraft certification was the goal of the EU-funded project 'Fiber optic sensors application for structural health monitoring' (FOSAS).

Scientists sought to exploit fibre optic Bragg grating (FOBG) sensors for strain evaluation to predict initiation of corrosion. Fatigue corrosion is a complex phenomenon of degradation due to both mechanical cyclic stress and a corrosive environment. Although the individual effects have been studied extensively, their synergistic effects are not well understood. The team investigated both the electrochemical behaviour and mechanical strain of a metal coupon during fatigue testing in an aggressive environment. A FOBG sensor was used to monitor strain.

Development of improved SHM methods requires a suitable test apparatus. FOSAS also developed a tool to support development and certification of new SHM technologies for avionic materials and structures. It uses fibre optic sensors in place of traditional strain gauges. As a result of development work, the team has delivered a range of fibre optic SHM sensors. A single FBG sensor monitors quasi-static strain and high-frequency damage signals simultaneously, and another FBG sensor measures tri-axial strain and temperature simultaneously.

Finally, the team targeted a novel distributed temperature-sensing system with ultra-high resolution based on standard optical fibres and swept wavelength interferometry. The technique converts a spectral shift to a temperature change. After a market analysis to see which technologies on the market were affordable and had the potential for aircraft certification, a distributed sensing technique was developed. The prototype system was tested in a ground test campaign and has been certified for laboratory use.

FOSAS has adapted numerous advanced fibre optic SHM technologies for aeronautical certification and use, and delivered tools for further development. Adoption of these advanced, low-cost technologies will significantly enhance the safety of the aircraft industry while reducing costs associated with operation and maintenance. Enhancing the competitiveness of the EU aerospace sector will have important benefits for the European economy.