Detection of Fatigue Cracks in Multi-layered Aircraft Components using Guided Ultrasonic Waves

The novel nondestructive testing (NDT) methodology described in this proposal will develop and demonstrate the application of guided ultrasonic waves for structural health monitoring (SHM) in complex, multi-layered structures, such as aircraft wings. The potential for the rapid and cost-efficient permanent monitoring of large surface areas of complex technical structures will be shown, allowing faster and more frequent inspections and monitoring at a lower cost, thus improving the reliability and safety of the inspected structures for a large number of industries. The proposed programme of work will tackle the real NDT problem in aerospace industry of the detection and monitoring of fatigue cracks in aircraft and demonstrate the proposed novel SHM technology for aerospace industry. In addition, fundamental research on guided ultrasonic waves propagation in complex, multi-layered structures will be conducted, laying the base for the application of the methodology for applications in a range of industries important to the UK economy, such as oil and gas exploration.Aircraft and other technical structures are subject to cyclic loading, e.g., during take-off, landing, manoeuvring, and adverse weather conditions. Such operating conditions can lead to the development of faults during the lifecycle of the structure. The skin of aircraft wings consists of multi-layered structures, connected using fasteners and rivets. Due to the stress concentration at the bolt holes of the fastener, fatigue cracks can start to develop from the edge of the hole during the service life of the aircraft. This damage can lead to the malfunction and ultimately failure of such structures, endangering lives. Therefore the integrity of such structures needs to be tested regularly or monitored using NDT methods. The novel methodology proposed here will result in the rapid and cost-efficient inspection and permanent monitoring of large surface areas of complex technical structures using guided ultrasonic waves. Guided waves can propagate over large distances in thin structures, allowing faster and more frequent inspections and monitoring of large surface areas at a lower cost, thus improving the reliability and safety of the inspected structures for a large number of industries. The significant, step change proposed here is to work on real, complex, multi-layered aircraft structures and to investigate and find ways to deal with the complexity of the guided wave propagation and scattering. Fatigue crack growth during cyclic loading will be monitored. Appropriate measurement equipment for guided waves in multi-layered structures will be developed and tested. The sensitivity and reliability of the proposed method for the detection of fatigue cracks at fastener holes in the different layers will be investigated and ascertained. Due to the propagation of the energy of the guided wave along the structure, the potential exists to improve the detection sensitivity in the middle (2nd) layer in such a multi-layered structure and to reduce inspection time and thus costs. The technology will be applied to real aircraft components and structures, and practical application experience gained, demonstrating the potential for the increase of inherent safety and cost reduction in further applications. In addition to the verification of the proposed SHM technology, fundamental research on guided ultrasonic waves propagation in complex, multi-layered structures will be conducted, laying the base for the application of the methodology in other important industries.