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Smart Structures and Systems
  Volume 25, Number 4, April 2020, pages 423-432

EMI based multi-bolt looseness detection using series/parallel multi-sensing technique
Dongdong Chen, Linsheng Huo and Gangbing Song

    In this paper, a novel but practical approach named series/parallel multi-sensing technique was proposed to evaluate the bolt looseness in a bolt group. The smart washers (SWs), which were fabricated by embedding a Lead Zirconate Titanate (PZT) transducer into two flat metal rings, were installed to the bolts group. By series connection of SWs, the impedance signals of different bolts can be obtained through only one sweep. Therefore, once the loosening occurred, the shift of different peak frequencies can be used to locate which bolt has loosened. The proposed multi input single output (MISO) damage detection scheme is very suitable for the structural health monitoring (SHM) of joint with a large number of bolts connection. Another notable contribution of this paper is the proposal of 3-dB bandwidth root mean square deviation (3 dB-RMSD) which can quantitatively evaluate the severity of bolt looseness. Compared with the traditional naked-eye observation method, the equivalent circuit based 3-dB bandwidth can accurately define the calculation range of RMSD. An experiment with three bolted connection specimens that installed the SWs was carried out to validate our proposed approach. Experimental result shows that the proposed 3 dB-RMSD based multi-sensing technique can not only identify the loosened bolt but also monitor the severity of bolt looseness.
Key Words
    bolt looseness detection; PZT; impedance; series/parallel multi-sensing technique; equivalent circuit; 3 dB-RMSD
(1) Dongdong Chen, Linsheng Huo:
State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning, 116023, People's Republic of China;
(2) Gangbing Song:
Smart Materials and Structures Laboratory, Department of Mechanical Engineering, University of Houston, Houston, TX, 77004, United States of America.

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