Vasiljevic Milos, Kundu Tribikram, Grill Wolfgang, Twerdowski Evgeny
Department of Civil Engineering and Engineering Mechanics, University of Arizona, Tucson, Arizona 85721, USA.
J Acoust Soc Am. 2008 May;123(5):2591-7. doi: 10.1121/1.2902188.
Most investigators emphasize the importance of detecting the reflected signal from the defect to determine if the pipe wall has any damage and to predict the damage location. However, often the small signal from the defect is hidden behind the other arriving wave modes and signal noise. To overcome the difficulties associated with the identification of the small defect signal in the time history plots, in this paper the time history is analyzed well after the arrival of the first defect signal, and after different wave modes have propagated multiple times through the pipe. It is shown that the defective pipe can be clearly identified by analyzing these late arriving diffuse ultrasonic signals. Multiple reflections and scattering of the propagating wave modes by the defect and pipe ends do not hamper the defect detection capability; on the contrary, it apparently stabilizes the signal and makes it easier to distinguish the defective pipe from the defect-free pipe. This paper also highlights difficulties associated with the interpretation of the recorded time histories due to mode conversion by the defect. The design of electro-magnetic acoustic transducers used to generate and receive the guided waves in the pipe is briefly described in the paper.
大多数研究人员强调检测来自缺陷的反射信号对于确定管壁是否有损伤以及预测损伤位置的重要性。然而，缺陷产生的小信号通常隐藏在其他到达的波模式和信号噪声之后。为了克服与在时间历程图中识别小缺陷信号相关的困难，本文在第一个缺陷信号到达后以及不同波模式多次在管道中传播之后，对时间历程进行了充分分析。结果表明，通过分析这些延迟到达的散射超声信号，可以清晰地识别出有缺陷的管道。传播的波模式在缺陷和管道端部的多次反射和散射并不妨碍缺陷检测能力；相反，它显然稳定了信号，使得区分有缺陷的管道和无缺陷的管道变得更容易。本文还强调了由于缺陷导致的模式转换而在解释记录的时间历程时所面临的困难。本文简要描述了用于在管道中产生和接收导波的电磁声换能器的设计。
