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11 April 2007 Effect on detection sensitivity for smart washer configuration and ambient temperature characteristics on bolted joint
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The objective of this study is to apply the concept of structural health monitoring to the detection of bolted joints loosening without human involvement. This paper proposes a method of bolt loosening detection by adopting a smart washer with sub-space state space identification (4SID) algorithm. The smart washer is the cantilevered plate type washer bonded piezoelectric material. The feature is the self-sensing and actuation function. The principle of how to detect the loosening of a bolt is the basis that the natural frequency of a smart washer system vary depending on a bolt tightening axial tension. The natural frequency of the smart washer was identified by using the sub-space state space identification method. For practical use of the smart washer, it is necessary to investigate the problem of repeatability and data quality depending on the influence of the ambient temperature characteristics, and to improve the sensitivity at the initial state of the bolt tightening axial tension decreasing. This paper describes the results of experimental and analytical about the effect on the sensitivity for the smart washer configuration, and the ambient temperature characteristics on the bolted joint. The experimental results indicate the influence of the temperature variation to the bolt tightening axial tension. In order to the sensitivity of the improve bolt loosening detection, vibration-modal analysis of the smart washer system is performed for the configuration of the smart washer. The design parameters of the smart washer was discussed on the results of the numerical simulation.
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Masayuki Okugawa and Tohru Tanaka "Effect on detection sensitivity for smart washer configuration and ambient temperature characteristics on bolted joint", Proc. SPIE 6532, Health Monitoring of Structural and Biological Systems 2007, 653213 (11 April 2007);

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