Research On Strain Transfer Theory Of Embedded Armored Fiber Bragg Grating Sensors

As a new high-performance sensor,Fiber Bragg Grating sensor plays an increasingly prominent role in various fields,such as structural health monitoring.Due to certain deflects of Fiber Bragg Grating and current construction characteristics,Embedded Armored Fiber Bragg Grating Sensors are required to protect the Fiber Bragg Grating in a better way.When this kind of sensor is applied in real structure,there exists difference between the actual strain and the strain measured by senor,and such difference is caused by the protection layer.Based on actual engineering requirement and current transferring theory insufficiency,theoretical and numerical researches are conducted on Embedded Armored Fiber Bragg Grating Sensor,including the sensor's transferring relationship,transferring efficiency and influential factors.A few useful conclusions and formulas are obtained to help choosing sensor type and validate the data accuracy.Firstly,based on the existence fiber Grating sensors strain transferring theory,a few reasonable assumptions are adopted to establish the strain transferring efficiency theory of Embedded Armored FBG sensor under axial force.Considering the influence of matrix material and multilayer structure,two formulas are derived to predict the strain transfer ratio at various points along the Embedded Armored FBG sensor and the average strain transfer ratio,containing the matrix shear elasticity modulus of such multilayer structure sensor.Some useful conclusions are obtained: the transferring rate increases with the matrix elastic modulus,the transferring efficiency change rate is remarkable when the matrix elastic modulus is less than 10 GPa,and the middle layer delimitations also have a certain impact on the transferring efficiency.These conclusions provide a useful reference for the actual sensor selection.Secondly,a finite element model of embedded armored FBG sensor is developed using ANSYS.The influence of multilayer structure and the elastic modulus of matrix material on the transferring efficiency are analyzed.High consistency is found between theoretical results and finite element simulation results by comparison,however,great differences exist between theoretical formula calculations and numerical analysis results when the elastic modulus of matrix is small.Thirdly,similarity theory and empirical formula deduction method is described,and studies subjects are determined based on the transferring theory and data support is provided by finite element experiments.Similarity criterion theory is used to establish a strain transferring efficiency empirical formula with low elasticity modulus of the matrix,and correction is made on the theoretical formula,obtaining the strain transferring efficiency empirical formula when the elastic modulus of the matrix is small.The application range of theoretical formula is improved to provide a reference for using Embedded Armored Fiber Bragg Grating sensors.