Adhesive bonded joints are frequently adopted in structural applications. The adhesive aging, low quality of surface preparation, as well as the exposure to external harsh environment and loading, may degrade the quality of adhesive, leading to disbond and decrease of the interfacial strength of the bonded joints. This study addresses both numerical and experimental investigations of ultrasonic guided wave (UGW) propagating in adhesive bonded metallic waveguide, whereby disbond detection is realized based on variation of the wave arrival time of UGW. First the dispersion curves of UGWs in both intact (bonded) and disbonded joints are obtained via the Semi-Analytical Finite Element (SAFE) method, and are grouped into mode pairs of phase velocity match and mis-match, respectively. Then a model combining SAFE and Frequency Domain Finite Element (SAFE-FDFE) is developed to enable excitation of any UGW of desired single mode-frequency combination and analysis of the wave interaction with disbond. The obtained results indicate that the UGW Mode 2 generated at the low frequency range of the mis-matched group shows a good sensitivity to disbond, featuring variation of the wave arrival time induced by mode conversion. Finally, Time Domain Finite Element and a proof-of-concept experiment, with comb transducers to act as both in situ actuators and sensors made of PVDF sheets embedded into the adhesive layer, well validate the results obtained via SAFE-FDFE. The selected mode-frequency combination Mode 2 at 0.52 MHz for wave time-of-arrival-based disbond detection, compared with conventional signal-amplitude-based disbond indicator using high frequency UGWs (~several MHz), merits the advantages of better controllability of wave excitation, less wave attenuation, and higher robustness.

中文翻译：

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使用导波的飞行时间变化在胶粘多层金属接头中进行原位脱粘检测

在结构应用中经常采用粘合剂粘合接头。胶粘剂老化、表面处理质量低下以及暴露在外部恶劣环境和负载下，可能会降低胶粘剂的质量，导致粘合接头的脱胶和界面强度降低。本研究解决了超声导波 (UGW) 在胶粘金属波导中传播的数值和实验研究，其中基于 UGW 波到达时间的变化实现了脱粘检测。首先通过半解析有限元（SAFE）方法获得完整（粘合）和脱粘接头中UGW的色散曲线，并分别分组为相速度匹配和失配模式对。然后开发了一个结合 SAFE 和频域有限元 (SAFE-FDFE) 的模型，以启用所需单模频率组合的任何 UGW 的激励，并分析与脱粘的波相互作用。得到的结果表明，在失配组低频范围内产生的UGW Mode 2表现出良好的脱粘敏感性，其特点是模式转换引起的波到达时间变化。最后，时域有限元和概念验证实验，使用梳状换能器作为原位致动器和传感器，由嵌入粘合剂层的 PVDF 片制成，很好地验证了通过 SAFE-FDFE 获得的结果。选定的模式-频率组合模式 2 在 0.52 MHz 时用于基于波到达时间的脱粘检测，