Fiber Optic Sensors for Detection of Corrosion within Aircraft

Abstract

The cost of preventing and controlling corrosion in aging aircraft fleets is becoming a significant burden. Early detection of corrosion will reduce the maintenance required to repair the damage, which should result in increased aircraft availability and significant reduction in the cost of ownership. Fluorescent fiber optic sensors that detect aluminum cations from the early stages of the corrosion process are proposed as a means for providing early warning of corrosion in susceptible areas of an aging aircraft. This article will discuss the results for two different carriers of an aluminum-sensing fluorophore and some of the key technical issues that need to be resolved for the development of an effective fiber optic sensing system.

Optical Fibres for Distributed Corrosion Sensing - Architecture and Characterisation

“…To monitor corrosion requires a sensor capable of measuring the changes that occur as a result of the corrosion process. Many of the aircraft fuselage components are fabricated from aluminium-based alloys, hence aluminium (Al) ions are of particular interest because they are not only an indicator of the onset of corrosion [1], but also have the potential to be an environmental hazard [5]. Optical fibre based sensors are inherently suited to distributed sensing [6] and are typically in the order of only a few hundred microns in diameter making them very lightweight and suitable for embedment in inaccessible corrosion-prone areas.…”

“…Optical fibre based sensors are inherently suited to distributed sensing [6] and are typically in the order of only a few hundred microns in diameter making them very lightweight and suitable for embedment in inaccessible corrosion-prone areas. In addition they can be functionalised to detect particular species of interest [1] such as Aluminium.…”

“…It is therefore essential that corrosion processes are monitored so that repair time and costs are minimised, and the structure is maintained in a safe operating condition. Corrosion is most difficult to detect in the hidden metallic structure of an aircraft, such as lap joints, stiffeners and under sealant beads, since access to these areas usually requires time consuming and therefore costly disassembly [1]. Such areas are recognised as being particularly prone to corrosion, due to the possibility of creating a micro-environment within the crevice between the plates, accelerating the corrosion process [4].…”

“…Such areas are recognised as being particularly prone to corrosion, due to the possibility of creating a micro-environment within the crevice between the plates, accelerating the corrosion process [4]. Current non-destructive inspection methods, typically based on the use of a hand held ultrasonic probe, require a 5-10% section loss for corrosion to be reliably detected, at which stage the damage may be too severe to repair, and so the component often needs to be replaced [1]. Clearly a more proactive approach is needed to detect the initial onset of corrosion within these difficult to inspect areas.…”

“…Typically, military aircraft have a planned life-of-type of 25-30 years. In Australia, in many cases, almost twice this time is achieved before the aircraft is retired [1]. For civilian aircraft flying today, approximately 20% are considered to be aging, and as that number increases so does the need for heightened fleet monitoring by airlines and manufacturers [2] and continued intense focus and surveillance of these activities by regulatory agencies [3].…”