FBG-based force sensing with temperature self-compensation for smart bolts

Small variations in bolt component connection can have significant impacts on equipment operating safety and efficiency. A comprehensive understanding of the bolted status supports the equipment optimizing in in-situ health monitoring. Therefore, an improved bolt force measurement method is looking forward. Given the minimally invasive nature, potential for multi-parameter measuring, and ability to operate in harsh conditions, optic fiber sensors present an opportunity for equipment in-situ health monitoring. This paper first strengthened the confidence in embedding optic fiber force sensors within the bolts. Additionally, the FBG temperature self-compensation method is employed and successfully improved the force measurement accuracy, compared with the existing studies. The smart bolt configuration (addictively manufactured) refers to the standard bolt dimensions and integrates a metallized FBG optical fiber with a diameter of less than 0.5 mm. Then, the sensor performance was investigated through a series of routine mechanics tests and reports the force sensitivity of the designed smart bolt is 13.06 pm/kN (for M10 bolts) and 14.59 pm/kN (for M12 bolts), respectively. In dynamic force loading tests, the error of the sensor is within 4.95 %, and the maximum force detection error after temperature compensation is within 8.03 %, indicating an improved bolt force measuring accuracy. The anti-creep and anti-torque interference tests were undertaken to confirm the designed smart bolts are adequate for long-term service. The bolt vibration and connection test results have proved the mechanical solidity and reliability under extreme working conditions. This investigation confirms the viability of installing optic fiber force sensors in a bolt component. Confidence was established that the smart bolts have the advantages of compact structure, improved force detection accuracy, good reliability, and support for modern equipment in-situ health monitoring.