Fibre Optic System for Deflection & Damage Detection
Integrated Microsystems Austria (IMA)
The motivation behind the development of morphing wings is biologically inspired by the flight capabilities of birds. They are able to achieve a wide dynamic range missions through large shape changes to their wings. There are several examples in aircraft industry where morphing wing approach is already tested with good results in terms of tuneable aerodynamic properties. However, a big challenge in the art still exist how efficiency to control the flight by morphing wing concept without damages possible induced in the composite materials such as carbon- or glass-fibre reinforced plastics (CFRP and GFRP). In order to guarantee the structural integrity and airworthiness of such a component continuous inspections with regard to damage evolution have to be done.
Currently all non-destructive inspections are performed on ground following a fixed time schedule where the number of inspections per time increases significantly with the age of the aircraft (Time Based Maintenance).
If the sensors and / or actuators of a non-destructive inspection and load monitoring system could be permanently attached to the structure of interest (self sensing structure) and the system operated online during service (Structural Health Monitoring), especially in distributed and difficult to access areas, the way is open for a paradigm change to maintenance on demand (Condition Based Maintenance). In this project we propose a new technique based on low coherence interferometry performed in “all-in-fibre” sensing configuration, made of single mode optical fibre. The strain sensing element is a coil made of several turns of optical fibre, firmly fixed on the surface of the subjected structural part. These sensors will be used to acquire low frequency strains for the determination of the deflection and at the same time acquire the high frequency strains arising from the onset, growth and friction of damages (AE events). In such configuration only a limited number of sensors is required to characterize the damage as AE is the only passive technique that is able to cover larger areas with a sufficient size of detectable damage.
In general, key questions to be answered by the system developed in this project are:
- What is the direction of deflection of composite wing?
( qualitative awareness)
- What is the magnitude of deflection of composite wing? (quantitative awareness)
- Does the damage exist at all? (qualitative awareness)
- Where is the damage? (quantitative localization); and
- What is the size and severity of damage? (quantitative assessment of damage).