Abstract
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 achieve 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 and the human operation. In this study, a smart washer was proposed to detect the loosening without human involvement. The basic principle of how to detect the bolt loosening is based on the smart washer dynamics perturbation depending on the tightening axial tension for bolted joint. The smart washer used in this study is in cantilever type with piezoelectric material, which adds the washer of the self-sensing and actuating function. Previous research had indicated that a correlation was confirmed between the natural frequency of the smart washer and the tightening axial tension with the theoretical and experimental results. The subject of this method is to identify the natural frequency of the smart washer by changing the bolt tightening axial tension, which is using the self-sensing and actuating by applying the piezoelectric material. In this paper describes the natural frequency identification method for smart washer with the adaptive observer by variable adaptive law. While the tightening axial tension changes, the initial parameter vector is updated every investigation period. It is appropriate that the identified value just before the investigation period is adopted as the initial parameter vector for new period. The influence of initial parameter vector will be considered with simulations when applying the adaptive observer.
