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Ultrasound detection of damage in complex carbon fibre/metal structures

机译:超声检测复杂碳纤维/金属结构中的损伤

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We describe work carried out to monitor the structural health of a complex structure comprising both carbon fibre and metal components using ultrasound techniques. The work is designed to be used in a high performance car, but could find applications in other areas such as the aerospace industry. There are two different types of potential problem that need to be examined; the first is damage (e.g. holes, delaminations) to carbon fibre structure, and the second is damage to joints either between two carbon fibre components or between a carbon fibre component and a metallic one. The techniques used are based around the use of PZT transducers for both the generation and detection of ultrasonic Lamb waves. To date we have been carrying out experiments on mock-up samples, but are due to conduct tests on an actual vehicle. Lamb waves propagate in modes whose order is determined by the frequency thickness product. Their properties, such as phase and amplitude can be modified by the presence of damage, such as holes and delaminations. If we record the response of a healthy structure, we can then compare it with signals obtained on subsequent occasions to determine if any significant change has taken place. It is essential, however, to be able to differentiate between the effects of damage and those of environmental changes such as temperature. For this reason we have monitored the response of a sample at different temperatures both before and after drilling a hole in it to simulate damage. Depending on the positions of the transducers with respect to the damaged area, it is possible to detect either attenuation of the entire signal or changes in a specific portion of the signal produced by reflections. Results from these experiments will be presented at the conference. Signal processing techniques for separating damage from the effects of temperature will also be discussed We also look at the deterioration of joints, which can either be epoxy bonded (carbon fibre to carbon fibre) or bolted together (carbon fibre to aluminium). In the case of the bonded structures we are looking at the effects of failure of the bond layer, whilst in the case of the bolted samples we are looking at loosening of the bolts. The debonding was simulated by joining together a flat plate of carbon fibre composite with an L-shaped carbon fibre piece using a couplant such as grease. Similar experiments were carried out using an aluminium anglebar bolted to the plate, with the bolts both tightened and loose. Signals of both the transmitted wave in the plate and the power coupled to the L piece were measured before and after debonding. This gives a more reliable measure of the change in power transfer between the two components as the joint/bond degrades. It was found that in order to get maximum coupling to the second component the frequency of the acoustic wave had to be altered. This is because in the bonding region the combined thickness of the components alters the modal propagation characteristics of the structure compared with those of the single component region.
机译:我们描述了使用超声技术监测包含碳纤维和金属成分的复杂结构的结构健康状况的工作。该作品被设计用于高性能汽车,但可以在航空航天工业等其他领域找到应用。有两种类型的潜在问题需要检查;第一个是对碳纤维结构的损坏(例如孔洞,分层),第二个是对两个碳纤维组件之间或碳纤维组件和金属组件之间的接头的损坏。所使用的技术基于将PZT换能器用于产生和检测超声波兰姆波。迄今为止,我们一直在对模型样品进行实验,但由于要在实际车辆上进行测试。兰姆波以其顺序由频率厚度乘积确定的模式传播。它们的特性(例如相位和幅度)可以通过存在损坏(例如孔和分层)来进行修改。如果我们记录了健康结构的响应,则可以将其与在后续场合获得的信号进行比较,以确定是否发生了任何重大变化。但是,必须能够区分损害的影响和环境变化(例如温度)的影响。因此,我们在样品上钻孔之前和之后都监测了样品在不同温度下的响应,以模拟损伤。根据换能器相对于受损区域的位置,可以检测整个信号的衰减或反射产生的信号特定部分的变化。这些实验的结果将在会议上介绍。还将讨论将损坏与温度影响分开的信号处理技术。我们还将研究接头的劣化,该接头可以通过环氧树脂粘结(碳纤维与碳纤维)或用螺栓固定在一起(碳纤维与铝)。对于粘结结构,我们正在研究粘结层失效的影响,而对于螺栓连接的样品,我们正在研究螺栓的松动。通过使用诸如油脂的耦合剂将碳纤维复合材料的平板与L形碳纤维片连接在一起来模拟剥离。使用螺栓固定在板上的铝制角铁进行了类似的实验,螺栓既拧紧又拧松。在剥离之前和之后,测量板中的透射波和耦合到L片的功率的信号。当接合/键退化时,这给出了两个组件之间功率传输变化的更可靠的度量。已经发现,为了获得与第二分量的最大耦合,必须改变声波的频率。这是因为与单个部件区域相比,在结合区域中部件的组合厚度改变了结构的模态传播特性。

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