Real-time monitoring of bolt clamping force at high temperatures using metal-packaged regenerated fiber Bragg grating sensors. (May 2019) - Tu, Yun
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.