An FBG based smart clamp fabricated by 3D printing technology and its application to incipient clamp looseness detection

Distributed block clamps are widely used in hydraulic piping systems to fix the pipeline and to adjust the natural frequencies of pipes. However, the clamps may get loosen due to wear over time, and if not detected, it will lead to catastrophic failures. Piezoelectric lead Zirconate Titanate (PZT) based active sensing methods have been widely used to monitor the looseness of the bolted structures. However, this method bears some drawbacks, e.g., saturation, electromagnetic interference and high cost. Therefore, Fiber Bragg Grating (FBG) based sensing technology, which is robust to electromagnetic interference and easy for multiplexing, has been employed to design smart bolts and washers to monitor the preload of the bolted structures in existing literatures. However, the applications of those structures are limited due to specific customization, e.g. the distributed feature of the smart bolt is limited by the blind hole structure and the smart washer can only be used to the bolted connections with big-diameter bolts. To address these issues, a smart clamp is presented in present study. Moreover, the 3D printing technology is also investigated to fabricate FBG based smart clamps in a flexible and cost-effective way. A novel FBG based smart clamp is proposed in this work. The influence of different print layer heights, 0.15mm and 0.2mm on the sensitivity of clamp is also evaluated. It is shown that the 0.2mm height leads to a higher sensitivity than the 0.15mm height. Its application to incipient clamp looseness detection is further performed in an industrial piping system.