Real-time monitoring of bolt clamping force at high temperatures using metal-packaged regenerated fiber Bragg grating sensors

Abstract

Inappropriate clamping force in bolted flange joints operated at high temperatures has been regarded as the main issue that endangers the reliability and safety of a plant. In order to accurately and reliably measure the bolt clamping force, an innovative technique is proposed using metal-packaged fiber Bragg grating (RFBG) sensors. A metal-packaged RFBG sensor is developed by a combination of magnetron sputtering and electroplating followed by spot-welding on a bolt, and calibrated by uniaxial tensile and thermal tests. The clamping force in a bolted steel-steel joint is monitored by the metal-packaged RFBG sensor spot-welded on the bolt and analyzed by a finite element model. The sensor exhibits good linear response to axial loads applied to the bolt when exposed to constant high temperatures up to 500 °C, as well as good stability and repeatability. Its thermal response is non-linear and can be expressed as a cubic-polynomial function of temperature. The variation of the clamping force in the bolted joint subjected to thermal loading is then monitored by the sensor, which is further verified by a comparison of the experimental results and the numerical predictions showing a satisfactory agreement. The results demonstrate that this technique provides a new possibility for real-time monitoring of bolt clamping force and structural health monitoring of bolt joint structures operating in high-temperature environments.