The development of a fiber Bragg grating based smart washer

Long time lasted micro vibration will easily cause the looseness of bolts. It is critical for the health and safety monitoring of bolt looseness. Although many remarkable bolt looseness detection approaches already been developed in recent years, it is still difficult to the quantitatively evaluate the bolt degradation without do any harm to the bolt. In this article, a FBG (Fiber Bragg Grating) embedded smart washer was proposed to monitor the looseness of bolt connection and the theory analysis were induced to verify the linear tendency of smart washer annular strain. Two experiments were carried out to verify the analysis: first of all, the relationship between applied torque and bolt tension were investigated. A smart bolt which made by embedding FBG sensor into the bolt was used in the specimen and the experiment result indicates that bolt axial tension is linearly with applied torques which also consistent with previous researches. Then, the experiment which fabricated with smart washer and smart bolt was implement. The linear relationship between pre-load change and the wavelength increment was obtained. The analytical and experimental results both demonstrate that the proposed novel approach in this study is very sensitive to the bolt pre-load degradation and it is robust in monitoring the blot looseness.