Rapid Inspection of Complex Geometries Using Edge-Guided Ultrasonic Waves

薄板中的超声波具有许多有趣的特性，例如随频率变化的速度以及在给定频率下多种可能的振动模式。该项目将使用一组特殊的模式，沿着薄板的边缘，创建一种监测碳纤维增强聚合物（CFRP）飞机部件边缘损伤的方法。结构健康监测，即对工程结构进行持续的损伤测试，使工程结构的使用寿命管理方式得到显著改善。基于设计结构在其计划工作寿命之外长期可行的方法正在被依赖于监测最初劣化迹象然后进行适当修复或更换的方法所取代。这使得更轻的结构可以安全使用，从而大大节省了建筑材料，并且对于飞机，船舶和汽车等结构，在其整个使用寿命中提高了效率。超声波已经成功地应用于板状结构和管道的结构健康监测，但具有复杂几何形状和随方向变化的物理性质的结构（各向异性材料）对超声波结构健康监测提出了特殊的挑战。这项工作将产生对各向异性材料中边缘导波的理解，作为一种测试复杂结构重要部分的方法。由于超声波在薄片状结构中传播时，由于结构表面的影响，限制了可能的形状（或模态），因此超声波在薄片状结构中的行为比在块状材料中传播的波具有更复杂的行为。这些导波可以传播很远的距离（高达几十米），并被缺陷散射，使它们能够用于检测损伤。它们也可以在任何给定频率下具有多种模式，每种模式都具有不同的频率相关速度，这使它们的使用变得复杂。在寻找将其应用于损伤检测的方法方面已经做了大量的工作。超声波在薄结构边缘的行为由于边缘也充当波的向导而进一步复杂化。这导致沿板边缘传播的模态，但从边缘迅速衰减。除了代表一个有趣的物理问题外，这些模式，统称为边缘波，是检查复杂几何结构重要部分问题的候选解决方案。特别是，它们非常适合检查薄结构边缘的损坏，例如：机翼面板的加强筋或飞机的控制面，涡轮叶片或暴露的钢梁。检查翼板加强筋（垂直于面板以防止其弯曲的小板）是很有趣的，因为它们特别容易受到损坏并承载重大载荷。为了实现这一应用，需要实现以下目标：在各向异性材料中建立边缘波的数值模型，设计产生和测量边缘波的方法，并在受损结构上进行实验以确定缺陷对边缘波的影响。将创建一种检查特定结构（翼板加强筋）的方法，并生成允许应用于检查任何薄结构边缘的损坏的技术。将制作一个演示系统来展示这项技术。

Ultrasonic waves in thin plates have a number of interesting properties, such as velocities that vary with frequency and multiple possible modes of vibration at a given frequency. This project will use one particular group of modes, which follow the edges of thin plates, to create a method of monitoring the edges of carbon fibre reinforced polymer (CFRP) aircraft components for damage. Structural health monitoring, whereby engineering structures are continually tested for damage, allows significant improvements in the way that the useful lifetime of engineering structures is managed. Methods based on designing structures to be viable long beyond their planned working life are being replaced by approaches that rely on monitoring for the first signs of deterioration and then repairing or replacing appropriately. This allows lighter structures to be used safely resulting in significant savings in construction materials and, for structures such as aircraft, ships and automobiles, improved efficiency throughout their working life. Ultrasonic waves have been successfully applied to structural health monitoring of plate-like structures and pipes, but structures with complicated geometries and physical properties that vary with direction (anisotropic materials) present particular challenges for ultrasonic structural health monitoring. This work will generate understanding of edge guided waves in anisotropic materials as a method of testing important sections of complicated structures.Ultrasonic waves in thin, plate-like, structures have more complicated behaviour than waves travelling through bulk materials due to the effect of the surfaces of the restricting the possible shapes (or modes) through the thickness of the structure as the wave propagates. These guided waves can travel large distances (up to tens of metres) and are scattered by defects, allowing them to be used to detect damage. They can also have multiple modes at any given frequency, each with a different frequency-dependent velocity and this complicates their use. Substantial work has been done to find methods of applying them to damage detection. The behaviour of ultrasonic waves at the edges of thin structures is further complicated by the edge also acting as a guide to the wave. This leads to modes that propagate along the plate edges, but decay rapidly away from the edge. In addition to representing an interesting physical problem, these modes, collectively referred to as edge waves, are a candidate solution to the problem of inspecting important parts of complicated geometry structures. In particularly they are ideally suited to inspecting for damage on the edges of thin structures such as: the stiffeners of wing panels or control surfaces of aircraft, turbine blades or exposed steel girders.The inspection of wing-panel stiffeners (small plates perpendicular to the panel to prevent it bending) is of interest as they are particularly susceptible to damage and carry significant loads. The following objectives will need to be achieved for this application to be realized: creating numerical models of edge waves in anisotropic materials, designing methods of generating and measuring edge waves, and performing experiments on damaged structures to determine the effect of defects on edge waves. A method of inspecting a specific structure (wing panel stiffeners) will be created and techniques generated to allow application to inspecting the edges of any thin structure for damage. A demonstrator system will be produced that showcases this technique.