Abstract Concrete causes substantial attenuation on ultrasonic guided waves during their propagation within a pipe. The circumferential position of the defect is even more difficult to detect in a concrete-covered pipe with a small diameter. This paper reports that the axial and circumferential positions of a circumference defect in a small-diameter concrete-covered pipe can be identified by moving the half-covered axial magnetised magnetostrictive patch transducer (AM-MPT) around the circumference of the pipe for subsequent measurements. First, the theory of normal mode expansion (NME) and demagnetisation is presented for the proposal of the nondestructive test (NDT) method and half-covered AM-MPT. Second, the NDT method based on NME is explained. Subsequently, the finite element models and experiments are applied to reveal the propagation of triggered and reflected non-axisymmetric guided waves L(M,2) to prove that the proposed method is applicable. Third, several frequencies of L(M,2) are compared to determine the best fit. The experimental results of pipes tested using half-covered AM-MPTs with different length–width ratios of iron cobalt patches proved that the greater the length–width ratio, the greater the amplitude of L(M,2) signals. These results support the theoretical results for the demagnetising field. The signals received from different circumferential positions of the pipe using AM-MPTs reveal that increasing the coverage of the transducer can improve the consistency of the signals received from the different circumferential positions. Next, the group velocity and attenuation characteristics of L(M,2) within the concrete-covered pipes were studied through experiments, with results matching the theoretical results. Finally, the experimental results proved that the proposed method could be utilised to determine the axial and circumferential positions of the defect in concrete-covered pipes. Moreover, the precision of the detection results can be improved by adding the monitoring position around the circumference of the pipe. It was demonstrated that the proposed method has potential to detect defects in concrete-covered pipes.

中文翻译：

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基于非轴对称导波能量分布变化的小直径混凝土包覆管缺陷周向定位方法

摘要 混凝土在超声波导波在管道内传播的过程中会导致显着衰减。在小直径的混凝土覆盖管中，缺陷的圆周位置更难以检测。本文报道，通过围绕管道圆周移动半覆盖轴向磁致伸缩贴片换能器 (AM-MPT) 进行后续测量，可以识别小直径混凝土覆盖管道中圆周缺陷的轴向和圆周位置. 首先，提出了正常模式扩展（NME）和退磁的理论，以提出无损检测（NDT）方法和半覆盖AM-MPT。其次，解释了基于 NME 的无损检测方法。随后，应用有限元模型和实验揭示了触发和反射的非轴对称导波 L(M,2) 的传播，以证明所提出的方法是适用的。第三，比较 L(M,2) 的几个频率以确定最佳拟合。使用不同长宽比铁钴补片的半覆盖 AM-MPT 测试管道的实验结果证明，长宽比越大，L(M,2) 信号的幅度越大。这些结果支持退磁场的理论结果。使用 AM-MPT 从管道的不同圆周位置接收到的信号表明，增加换能器的覆盖范围可以提高从不同圆周位置接收到的信号的一致性。下一个，通过实验研究了L(M,2)在混凝土覆盖管内的群速度和衰减特性，结果与理论结果相符。最后，实验结果证明该方法可用于确定混凝土覆盖管缺陷的轴向和周向位置。此外，通过在管道周围增加监测位置，可以提高检测结果的精度。结果表明，所提出的方法具有检测混凝土覆盖管道缺陷的潜力。实验结果证明，该方法可用于确定混凝土覆盖管缺陷的轴向和圆周位置。此外，通过在管道周围增加监测位置，可以提高检测结果的精度。结果表明，所提出的方法具有检测混凝土覆盖管道缺陷的潜力。实验结果证明，该方法可用于确定混凝土覆盖管缺陷的轴向和圆周位置。此外，通过在管道周围增加监测位置，可以提高检测结果的精度。结果表明，所提出的方法具有检测混凝土覆盖管道缺陷的潜力。