A Fiber Bragg Grating-Based Gap Elongation Sensor for The Detection of Gap Elongation in Bolted Flange Connection

Abstract

Many attempts havebeen madeby embedding a strain gauge sensor into thebolt shank to directly monitor the looseness of bolted structures. This application is constrained by many factors,including massive cabling connection, shortcomings of this sensor in harsh conditions,and low efficiency forhigh temperature applications.Therefore, fiber Bragg grating (FBG) sensingtechnology isa good alternative to solve the problem. In this article, an FBG-based gap elongation sensor wasdeveloped by embedding the sensor into a Teflon tube and clampingon the metal base structure. Several tests were carried out to calibrate the strain-sensitive coefficient of the sensor and also to determine the stability, linearity, and repeatability of the sensor for gap strain measurement. The strain sensitivity of the sensor was determined by a standard tensile test,with the strain sensitivity values ranging from 0.4221 pm/με to 0.5245 pm/με. During the calibration test, the FBG sensors showed excellent linearity and repeatability of less than 0.1% and 5% errors, respectively. Theexperimental resultsdemonstrated a linear relationship between the applied force and the FBG sensorwavelength. Furthermore, the experimental resultsdemonstrated acceptable linearity and stabilityof the sensor when subjected to bending loadswith overall repeatability errorsof less than 10%. This proposed method provides an alternativeapproach to monitor bolted gapelongation andcharacterize bolt looseness.