Enhanced Ultrasonic 3D Characterisation Of Composites Using Full Matrix Capture Of Array Data

近年来，在航空发动机的主要飞机结构和风扇叶片等安全关键部件中使用厚截面复合材料的兴趣与日俱增。所有这样的部件都需要在制造过程中接受无损评估(NDE)；这很耗时，而且NDE的生产能力在国际上已经达到了极限。目前的复合无损检测(NDE)是基于定性的经验方法，其中使用单个垂直入射超声探头来根据后壁反射的幅度来估计平均超声衰减。虽然这种方法足以接受或拒绝薄复合材料面板，但不能提供较大部件定量无损检测所需的缺陷表征和定位水平。工业上显然迫切需要定量无损检测技术，这种技术可应用于制造和使用中的安全关键复合材料部件。出于成本、安全性和易于部署的原因，超声波技术是工业首选的选择，但需要提高扫描速度以加快吞吐量。然而，快速扫描、高穿透深度和准确的缺陷表征的矛盾需求不能用单一的垂直入射探头来实现。相反，来自多个检查方向的数据必须组合在一起。使用超声阵列可以快速有效地获得所需的原始数据，但目前还不能开发。这是由于缺乏(A)适当的斜波传播和散射过程的正演模型，以及(B)将原始数据转化为有用信息的适当的反演方案。这就是拟议研究方案的动机，其目的是开发基于物理推理的超声阵列数据处理技术，以表征安全关键的航空航天复合材料。该计划需要推进复合材料中波动现象的基础科学，解决具有挑战性的逆问题，关键是将科学发现转化为实际的工业解决方案。

Recent years have seen increasing interest in the use of thick-section composites for safety-critical components in, for example, primary aircraft structure and fan blades in aero engines. All such components are required to undergo non-destructive evaluation (NDE) during manufacture; this is time consuming and NDE throughput is stretched to its limit internationally. Current composite Non-destructive Evaluation (NDE) is based on a qualitative empirical approach where a single normal-incidence ultrasonic probe is used to estimate the average ultrasonic attenuation from the amplitude of the back-wall reflection. While adequate for accepting or rejecting thin composite panels, this approach does not provide the level of defect characterisation and localisation necessary for the quantitative NDE of larger components.There is a clear and pressing industrial need for quantitative NDE techniques that can be applied to safety-critical composite components both at manufacture and in-service. An ultrasonic technique is the industrially preferred option for reasons of cost, safety and ease of deployment, but increased scanning speeds are required to speed up throughput. However, the conflicting demands of rapid scanning, high-penetration depth and accurate defect characterisation cannot be achieved with a single normal-incidence probe. Instead the data from multiple inspection directions must be combined. The necessary raw data can be rapidly and efficiently obtained using an ultrasonic array, but at present it cannot be exploited. This is due to the lack of (a) an appropriate forward model of oblique wave propagation and scattering processes, and (b) a suitable inversion scheme to turn the raw data into useful information. This is the motivation for the proposed research programme, the aim of which is to develop ultrasonic array data processing techniques based on physical reasoning for the characterisation of safety-critical aerospace composites. The programme requires advancement of the fundamental science of wave phenomena in composites, the solution of a challenging inverse problem and, crucially, the translation of the scientific findings into practical industrial solutions.