Development of a fiber optic health monitoring system for aerospace applications

Abstract

This paper describes our research activity involved in the identification, development and test of a prototype SHM system constituted by optical sensing nodes to measure both temperature and strain on ultra high temperature ceramics (UHTC) materials up to 1000 °C. Commercially available optic devices can operate up to 550 °C. To raise temperature limit up to 1000 °C, custom devices, mainly under development for scientific applications, have been identified. A prototype SHM system has been developed adopting a FBG sensor for temperature measurement and an EFPI sensor in sapphire fiber for strain measurement. The preliminary findings from thermo-mechanical tests indicate that former SHM system is capable of accurately measuring strain at elevated temperatures on UHTC materials.Structural Health Monitoring is an emerging technology lending to the development of systems capable of continously monitoring structures for damage with minimal human intervention. The goals of SHM systems are to improve reliability and safety while reducing maintenance costs, to minimize overall cost of ownership of a vehicle.In aerospace applications health diagnostics is an area where major improvements have been identified for potential implementation into the design of new reusable launch vehicles to reduce life-cycle cost, to increase safety margins and to improve mission reliability.Space vehicles perform in the temperature range from -150 o C in space up to 2000 o C reached during re-entry (order of magnitude, being strongly dependent from chosen reentry trajectory and vehicle configuration). As a result, space vehicles require high-performance TPS that provide high temperature insulation capability with lower weight, high strength and reliable integration with the existing system.Damage or failure of TPS without being detected can lead to a catastrophe. Accordingly, knowledge of the integrity of the TPS before each launch and re-entry is essential to the success of the mission.Our work aims to develop and test a prototype SHM system constituted by optical sensing nodes to measure both temperature and strain on UHTC materials up to 1000 °C. A prototype SHM system has been developed adopting a FBG sensor for temperature measurement and an EFPI sensor in sapphire fiber for strain measurement.The relevant aspect of the project relies in the application of a combined FBG/EFPI sensor to monitor both temperature and strain at high temperature. The experiment demonstrated the use of fiber optic technology in a temperature range (1000 °C) which is more severe than the usual fiber optic aircraft application (~200 °C) which represent the current market strain sensor limit. current fiber optic (FO) sensor technology has arisen largely on the basis of the optical components and especially optical fibers made available as a result of the growth in their use for telecommunication purposes.The use of FO sensors to measure strain and temperature or to detect damage in structures are finding more applications due to the following advantages:small siz...