Experimental Study on the Calibration of Unencapsulated FBG Strain Sensors Under Different Mounting Methods
[Objective]As a new type of strain measuring instrument,fiber bragg gratings(FBG)strain sensors are gradually used in the field of civil engineering,and the key to their use lies in the deployment of sensors and the calibration of sensitivity coefficients according to different usage requirements and environments.The cur-rent conventional FBG installation methods are direct surface adhesion and slotting implantation.[Method]In order to determine the measurement accuracy of the two installation methods,a calibration method of the un-packed FBG sensitivity coefficient used for the pile sinking test was proposed and the calibration test of the two deployment methods was carried out by using the circular seamless steel tube as the matrix,and the calibration results were compared with the theoretical values.[Result]The results show that in the stage of progressive load-ing,the calibration coefficient obtained by slotting implantation is smaller than that by surface adhesion,while the calibration coefficient obtained by the surface adhesion is closer to the theoretical value.The calibration coef-ficients obtained by slotting implantation and surface adhesion were 2.84%and 0.33%respectively compared with the theoretical values;In the step-by-step unloading phase,there is a certain lag in the central wavelength of the two deployment methods,but the calibration coefficient is not much different from that in the loading stage.[Conclusion]Therefore,it is necessary to choose a reasonable fiber grating layout scheme and calibration method according to the test environment and within the test tolerance range in the process of using FBG.
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