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

本提案中描述的新型无损检测（NDT）方法将开发和演示导波超声波在复杂多层结构（如机翼）中的结构健康监测（SHM）应用。将显示出对复杂技术结构的大面积进行快速和具有成本效益的永久监测的潜力，从而可以以较低的成本进行更快和更频繁的检查和监测，从而提高许多行业所检查结构的可靠性和安全性。拟议的工作方案将解决航空航天工业中飞机疲劳裂纹检测和监测的真实的NDT问题，并展示拟议的航空航天工业新型SHM技术。此外，还将对复杂多层结构中的导波超声波传播进行基础研究，为该方法在对英国经济至关重要的一系列行业（如石油和天然气勘探）中的应用奠定基础。飞机和其他技术结构会受到循环载荷的影响，例如，在起飞、着陆、操纵和恶劣天气条件下。这样的操作条件可能导致在结构的生命周期期间故障的发展。飞机机翼的蒙皮由多层结构组成，使用紧固件和铆钉连接。由于紧固件的螺栓孔处的应力集中，在飞机的使用寿命期间，疲劳裂纹可以从孔的边缘开始发展。这种损害可能导致这些结构的故障和最终失败，危及生命。因此，这些结构的完整性需要定期测试或使用NDT方法进行监测。这里提出的新方法将导致快速和具有成本效益的检测和永久监测的大面积复杂的技术结构，使用引导超声波。导波可以在薄结构中传播很长的距离，允许以较低的成本更快和更频繁地检查和监测大的表面积，从而提高了许多行业的被检结构的可靠性和安全性。这里提出的重要的步骤变化是在真实的、复杂的、多层飞机结构上工作，并研究和找到处理导波传播和散射的复杂性的方法。将监测循环载荷期间的疲劳裂纹扩展。将开发和测试多层结构中导波的适当测量设备。将研究和确定所提出的方法在不同层的紧固件孔的疲劳裂纹检测的灵敏度和可靠性。由于导波的能量沿着结构传播，因此存在改进这种多层结构中的中间（第二）层中的检测灵敏度并减少检查时间从而减少成本的可能性。该技术将应用于真实的飞机部件和结构，并获得实际应用经验，展示了在进一步应用中提高固有安全性和降低成本的潜力。除了验证所提出的SHM技术外，还将对复杂多层结构中的导波超声波传播进行基础研究，为该方法在其他重要行业中的应用奠定基础。

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.