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Sensors 2018, 18(6), 1928;

Preload Monitoring of Bolted L-Shaped Lap Joints Using Virtual Time Reversal Method

1,* , 1,2
School of Astronautics, Northwestern Polytechnical University, Xi’an 710072, China
Mechanical Engineering Department, University of Maryland Baltimore County, Baltimore, MD 21250, USA
Department of Mechanical Engineering, University of Bristol, Bristol BS81TR, UK
Author to whom correspondence should be addressed.
Received: 1 May 2018 / Revised: 5 June 2018 / Accepted: 12 June 2018 / Published: 13 June 2018
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L-shaped bolt lap joints are commonly used in aerospace and civil structures. However, bolt joints are frequently subjected to loosening, and this has a significant effect on the safety and reliability of these structures. Therefore, bolt preload monitoring is very important, especially at the early stage of loosening. In this paper, a virtual time reversal guided wave method is presented to monitor preload of bolted L-shaped lap joints accurately and simply. In this method, a referenced reemitting signal (RRS) is extracted from the bolted structure in fully tightened condition. Then the RRS is utilized as the excitation signal for the bolted structure in loosening states, and the normalized peak amplitude of refocused wave packet is used as the tightness index (TIA). The proposed method is experimentally validated by L-shaped bolt joints with single and multiple bolts. Moreover, the selections of guided wave frequency and tightness index are also discussed. The results demonstrate that the relationship between TIA and bolt preload is linear. The detection sensitivity is improved significantly compared with time reversal (TR) method, particularly when bolt loosening is at its embryo stage. The results also show that TR method is an effective method for detection of the number of loosening bolts. View Full-Text
Keywords: bolt preload monitoring; bolt joints; time reversal; structural health monitoring; guided wave bolt preload monitoring; bolt joints; time reversal; structural health monitoring; guided wave

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Du, F.; Xu, C.; Wu, G.; Zhang, J. Preload Monitoring of Bolted L-Shaped Lap Joints Using Virtual Time Reversal Method. Sensors 2018, 18, 1928.

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