Fly the friendly – and safer – skies
The safety of complex structures used in aircraft is typically evaluated via damage tolerance studies during the design cycle and regular time-based inspections during use. Automated non-destructive testing (NDT) techniques can drastically reduce the cost of inspection and enhance the detection of potential dangers via a condition-based maintenance plan. Such a plan incorporates continuous (rather than periodic) health monitoring using integrated sensor technology and automated damage assessment. The EU-funded ‘Aircraft integrated structural health assessment’ (AISHA) project evaluated the use of ultrasonic Lamb waves to selectively sense structural defects in aircraft components. In combination with signal processing routines for remaining lifetime prediction, the researchers also developed technology to evaluate fitness for service or need for repair. The investigators developed a database of 22 types of common structural aircraft materials (56 materials in total) along with their properties, degradation mechanisms under various loading conditions and NDT techniques. They developed an innovative Lamb wave driver and receiver system, enabling the generation of Lamb waves at a variety of frequencies with selective specificity for different kinds of defects. They thoroughly investigated and developed automated signal analysis techniques to ensure a precise relationship between monitoring results and actual structural condition. Thus, they could draw conclusions about structural integrity, remaining lifetime prediction and whether or not repair was advisable. The researchers carried out full-scale tests under realistic environmental conditions for three aircraft components: a helicopter beam made of a composite material, a helicopter beam made of an aluminium alloy and a slat track (a moving beam varying the wing surface available for lift) made of maraging steel. The onboard system reliably detected damage, appropriately located the damage position and maintained its functional integrity during intense mechanical vibrations. In summary, the AISHA project successfully developed a novel aircraft monitoring technology capable of evaluating structural integrity and reliable function under realistic conditions. The technology enables damage detection, localisation and evaluation of predicted remaining lifetime or need for repair. Thus, the commercialisation of the project outcomes promise enhanced European airline safety and thus enhanced consumer confidence, benefiting industry and travellers alike.
