Bolt Loosening Detection by Using Smart Washer with 4SID and Evaluation of Temperature Characteristics

Abstract

The objective of the present study is to apply the concept of structural health monitoring to the detection of loosening of a bolted joint without human involvement. This paper proposes a method of bolt loosening detection by adopting a smart washer which uses piezoelectric material with sub-space state space identification algorithm (4SID). The smart washer used in this study is in cantilever type with piezoelectric material, which adds the washer the self-sensing and actuation function. The principle used to detect the loosening of the bolts is a method of a bolt loosening detection noted that the natural frequency of a smart washer system is decreasing by the change of the bolt tightening axial tension. Therefore the study aims to identify natural frequency of a smart washer system adopting the system identification theory. The natural frequency of the smart washer was identified using sub-space state space identification method. Strong correlation was observed between the change of the natural frequency of the smart washer system and the decrement of bolt tightening axial tension. For more precise bolt loosening detection, the influence of the environmental temperature is also needed to be investigated. The experimental results indicate that the temperature change influence the bolt tightening axial tension.