Study On Sensing Characteristics And Measurement Errors Of Fiber Bragg Grating Dynamometry Bolts

The destruction of inner surrounding rocks in the roadway was hidden and difficult to detect.However,there were some flaws for the traditional detection method.(1)Vulnerable to external environment and complicated to process signals.(2)Cannot achieve long-term stable monitoring.(3)Cannot achieve distribution measurement.(4)Not conducive to long-distance information transmission.(5)Manually collecting data is prone to errors and is inefficient.To solve the above problems,sensing characteristics and measurement errors of fiber bragg grating(FBG)dynamometric bolt was studied and it was based on the fiber Bragg grating sensing theory.An FBG monitoring system for the distribution of the axial force of the bolt body was constructed in the 81303 return airway of Yanquan No.1 Coal Mine,and the stress of the bolt body was successfully monitored.In this paper,theoretical analysis,numerical simulation,laboratory tests and engineering practices were used to study the sensor characteristics and measurement errors of FBG dynamometric bolts.The main contents of this paper include:(1)The principle of FBG sensing,the design basis,structure principle and working principle of FBG dynamometric bolts were introduced.Based on the shear lag theory,it was considered that the strain sensed by surface-bonded FBG sensor was transmitted from the base material to the fiber grating in the form of shear strain through the adhesive layer.A mechanical analysis model was established.A standard linear model was used to describe the rheological properties of the adhesive layer.The instantaneous and quasi-static strain transfer efficiency of the FBG sensor was deduced.Combined with the sensing characteristics of the fiber grating,the stress formula of the bolt body could be derived.(2)The effects of shear modulus,length and width of the adhesive layer and thickNess of the interlayer on the strain transmission efficiency were analyzed by Matlab numerical simulation.(3)The stress formula of the bolt body was validated by uniaxial tension experiments.There was good correspondence between calculated values and experimental results.The static characteristics and measurement error of the measurement system were analyzed from the four evaluation indexes of measurement range,nonlinearity,sensitivity and return error,and the method of error compensation are proposed.(4)The underground pressure on-line monitoring system of FBG was introduced and applied to the 81303 return roadway of Yangmei No.1 Mine.Taking the force bolt as the research object,the axial force monitoring data of the bolts of the roadway roof,solid coal side and narrow coal pillar side when the monitoring section was approaching 5 m,20 m,50 m,70 m,90 m,and 110 m from the heading face were obtained.The FBG dynamometer monitoring data curve was similar to the theoretical stress curve of the full-length anchor bolt.At the same time,it was also very consistent with the plastic circle theory.The FBG dynamometer bolt could be used as a tool to monitor the strength of the bolt.