A tailless FBG smart bolt with excellent performance

The existing smart bolts based on fiber Bragg grating (FBG) have limitations, such as with long tail fibers and without satisfactory repeatability (R-squared value < 0.990), these limit their further application. Here, a tailless FBG smart bolt with excellent repeatability (R-squared value ≥ 0.999) that can simultaneously measure the strain and temperature through the design of the integrated FBG sensor is developed. A theoretical approach is employed to derive the linear relationship between the applied torque and the central wavelength of the tailless FBG smart bolt. The integrated FBG sensor embedded in the tailless FBG smart bolt, includes the temperature compensated FBG and strain measured FBG. In addition, a nominal strength of M24 bolt is redesigned. To enable the experimental study, the tailless FBG smart bolt is designed, fabricated and tested. Experimental results reveal the good linear relationship between the applied torque and the central wavelength of the integrated FBG sensor, which demonstrate that this tailless FBG smart bolt is suitable for the axial forces monitoring and the bolt looseness monitoring.