Electrical wires used in the aerospace industry can be considered as critical components to flight safety. There are more than 300 km of different types of wires in a typical aircraft with different shapes, from single insulated wire to bundles of multi stranded twisted wires. These wires are subject to variations in temperatures, pressure, and humidity level. As the wiring ages the insulation may become brittle or cracked and may suffer delamination from the core, becoming a potential source of unreliability or even a fire hazard. An example of that is the Trans World Atlantic (TWA) flight 800 crash, where all 230 passengers died due to an explosion caused by a sparking arcing wire near the fuel tank. Therefore, there is a need for a technique to examine the condition of insulated wiring.
This case study investigates the potential of utilising Long Range Ultrasonic (LRU) as an inspection technique to detect common type of flaws that can occur in aircraft wires.
- Characterise the behaviour of guided waves in aircraft wires. This includes wires consist of a single strand to multi strand twisted wire bundle.
- Indentify suitable wave mode that can propagate within the wire.
- Establish excitation/reception conditions to detect the desired wave mode.
- Demonstrate the ability of the desired wave mode to detect common types of flaws within the insulation materials of the wires.
Work conducted in this case described the behaviour of guided waves in terms of the phase velocity variation over frequency range for single wire with and without coating as well as wire bundles with different number of wires within the bundle itself. Seven wire bundles with different helix angles were also examined. The axi-symmetric wave mode has been identified as a suitable wave mode for propagation within the wire bundles and the detection of flaws in the insulation.
Excitation and reception conditions were designed to generate the axi-symmetirc wave mode. Two types of defects were created; these are in the axial and transverse plane.
LRUT uses the complex interaction between guided waves and the physical boundaries of the test piece to inspect from single point of access for many meters without removing insulation.
Potential future/other application areas using the approach/technique involved
Bridge cables, power cables and cable car
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