Ultrasonic Inspection for Complex Geometry

相控阵超声检测是无损检测中广泛使用的一种亚表面检测方法，由于它能够从一个位置进行多次检测，因此比标准超声检测能够以更高的置信度和精度定位和确定缺陷的大小。使用全矩阵捕获（FMC）获取数据，并且可以使用全聚焦方法（TFM）[2]产生超声波响应图像，从而提供检测区域缺陷的指示。除了从阵列到缺陷处的直接超声波外，还会有一波从被检材料的后壁反射过来，较晚到达缺陷处。这与FMC数据中的直接信号不同。这些反射波可以使用TFM[3]成像，从而可以从多个角度检查组件，以增加缺陷的检测率，并改善表征。通常，TFM的应用程序检查组件的区域，这些区域要么在阵列的正下方，要么靠近阵列[4-7]，换句话说，在阵列的视距（LoS）内。在无损检测中，优先检查最有可能产生缺陷的区域是常见的做法。在像飞机发动机这样的复杂部件中，这些区域很可能不是LoS。这导致在检查之前需要拆卸，增加了检查过程的成本。本研究项目旨在开发和验证一种方法，该方法能够通过反射来自组件几何形状的超声波来检测非视线（NLoS）区域。最初的目标是使用图1所示的简单测试用例来评估相控阵如何很好地评估这些区域。随后的目标是针对日益复杂的情况进行检查，包括抽象零件几何，各向异性材料或其几何或材料特性不精确已知的样品。最终，一种能够检查真实的工业相关样本的方法，使其在工业环境中的部署是合理的。到目前为止，工作的重点是开发一种基于射线的模型，以产生FMC数据，包括来自组件几何形状中任何单个壁（而不仅仅是后壁）的超声波反射，以及这些NLoS TFM图像中探头对侧钻孔（SDH）的预期灵敏度。32元5MHz探头对直径0.4mm的SDH的灵敏度如图2所示，其中多模tfm从侧壁反射聚焦。这些结果表明，在NLoS区域，有一些视图对理想缺陷具有不可忽略的灵敏度。虽然这是在理想条件下从缺陷中确定预期信号的有用工具，但它不能考虑实际系统中预期的随机和相干噪声。因此，通过比较几何结构内一系列位置缺陷的预期信号响应，这些结果与有限元模拟相比较，得到了验证。该项目的下一步是研究这种灵敏度与探针位置相对于几何形状的依赖程度，以确保可以可靠地检测到缺陷，并对实验结果进行验证。在此之后，模型的复杂性将增加，因为多边形各向同性固体的假设放宽到包括任意的各向异性几何，其尺寸可能不完全已知。最终，需要根据真实的工业相关样本验证开发的工具。

Phased array ultrasonic testing is a widely used method of sub-surface inspection in NDE, and is able to locate and size defects to a greater degree of confidence and precision than standard ultrasonic testing due to its ability to perform multiple inspections from one location [1]. Data is acquired using Full Matrix Capture (FMC), and an image of the ultrasonic response can be produced using the Total Focussing Method (TFM) [2], providing an indication of flaws in the inspection region. In addition to the direct ultrasonic wave from array to defect, there will be a wave which reflects from a back wall in the inspection material, arriving at the defect later in time. This appears distinct from the direct signal in the FMC data. These reflected waves can be imaged using TFM [3], enabling inspection of the component from multiple angles to increase the rate at which defects are detected, and improve characterisation. Typically, applications of the TFM inspect regions of the component which are either directly below or adjacent to the array [4-7] - in other words, within the array's line-of-sight (LoS). It is common practice in NDE to prioritise inspection of areas most likely to develop defects. In a complex part such as an aircraft engine, it is likely that these areas will not be LoS. This leads to the requirement for disassembly prior to inspection, increasing cost of the inspection process. This research project aims to develop and validate a method which is able to inspect non-line-of-sight (NLoS) areas by reflecting an ultrasonic wave from the geometry of a component. The initial goal is to evaluate how well a phased array can assess these areas using the simple test case shown in figure 1. Subsequent goals are to target the inspection of increasingly complex cases, including abstract part geometry, anisotropic materials or samples whose geometric or material properties are not precisely known. Ultimately, a method capable of inspecting real, industrially relevant samples such that its deployment in an industrial setting will be justified. Work so far has focussed on developing a ray-based model to produce FMC data including reflections of the ultrasonic wave from any individual wall in the component geometry rather than just the back wall, as well as the expected sensitivity of the probe to side-drilled holes (SDH) in these NLoS TFM images. The sensitivity of a 32-element 5MHz probe to a SDH with diameter 0.4mm is shown in figure 2, where multi-mode TFMs are focussed from side wall reflections. These results indicate that there are views which have non-negligible sensitivity to an ideal defect in NLoS areas. While this is a useful tool for determining the expected signal from a defect in ideal conditions, it does not account for random and coherent noise expected from a real system. These results were therefore validated against finite-element simulations by comparing the expected signal response from defects in a range of positions within the geometry. Next steps in the project are investigate how dependent this sensitivity is to the probe location with respect to the geometry, to ensure that defects can be reliably detected, as well as performing validation against experimental results. Following this, the complexity of the models will be increased, as the assumptions of a polygonal isotropic solid are relaxed to include an arbitrary, anisotropic geometry whose dimensions may not be exactly known. Ultimately, it will be a requirement to validate the tools developed against real, industrially relevant samples.