Bolted joints are widely used in mechanical and architectural structures . However , many serious accidents occur because of loosening in bolted joints , The diagnosis of the bolt loosening is able to be achieved by evaluating the variation of tightening axial tension . Conventionally , the inspection method of the loosening bolted joint is generally the measurement of the axial tension of a bolted joint by using ultrasonic waves . These methods require the use of special measurement equipment

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... nd . the human operation 」 n this study , a smart washer was proposed to detect the loosening without human involvement. The basic principle of how to deteot bolt loosenlng is to the dynamics characteristics of a smart washer system which varies depending on bolt tightening axial tension . A novel bolt loosening detection method by adaptive observer with variable gain is proposed in this paper. The numerical simulations are perfbmled to verif シ the possibility ofthe adaptive observer − based loosening detection .