Study On The Dynamic Strain Transfer Law Of Surface Bonded Fiber Bragg Grating Sensor

When the fiber Bragg grating sensor is used for the monitoring of mechanical equipment,the bare fiber Bragg grating or packaged is usually attached directly to the surface of the structure by the adhesive.As the mechanical properties between the optical fiber,the adhesive layer and the basis material are different,there is an error between the metrical strain of the FBG and the actual strain of the basal structure,which cannot be neglected in the high precision strain detection.At present,the research on strain transfer mechanism of fiber Bragg grating sensor is mainly based on that the force of the basis material is constant,but the load of the mechanical equipment is usually changed,the study on dynamic strain transfer law of fiber Bragg grating sensor is of great importance to improve the accuracy of strain detection in mechanical equipment.In this paper,the strain transfer model of the fiber Bragg grating under the sudden load is established based on the mechanical properties of the adhesive.The influence of the paste parameters on the strain transfer is analyzed.The theoretical analysis is verified by experiment.The theoretical analysis and experimental results show that: the instantaneous strain transfer rate of the surface-bonded fiber Bragg grating sensor is greater than that of the quasi-static strain due to the creep deformation of the adhesive when the basis structure is subjected to the sudden load.The length of the adhesive and the thickness of the intermediate layer have a great influence on the strain transfer rate of the fiber Bragg grating sensor.The instantaneous and quasi-static strain transfer rates of the fiber Bragg grating sensor augment with the increase of the bonding length,and the difference between the instantaneous strain transfer rate and the quasi-static strain transfer rate decreases with the increase of the paste length.When the basis structure is subjected to axial sudden load,the instantaneous and quasi-static strain transfer rates of the fiber Bragg grating sensor decrease with the increase of the thickness of the interlayer,and the difference between the instantaneous strain transfer rate and the quasi-static strain transfer rate increases with the augment of the thickness of the interlayer.The paste width and the paste thickness have little effect on the strain transfer of the fiber Bragggrating sensor,which can be ignored in fact.Then,the dynamic strain transfer law of the surface-bonded fiber Bragg grating sensor under the alternating load is analyzed by finite element analysis.The influence of the frequency of the load,the length,the width,the thickness of the adhesive layer and the thickness of the interlayer on the dynamic strain transfer rate of the fiber Bragg grating are analyzed.Finally,the excitation experimental system of equal intensity beam is built to verify the finite element analysis.The experimental results are in agreement with the results of the finite element analysis.The conclusions are drawn: the dynamic strain transfer rate of the fiber Bragg grating sensor varies litter with the load-frequency when the equal intensity beam is vibrated from 1 HZ to 100 HZ.The dynamic strain transfer rate of the fiber Bragg grating sensor augments obviously with the increase of patch length,and decreases a litter with the increase of the thickness of the adhesive layer.When the substrate is subjected to axial load,the dynamic strain transfer rate of the fiber Bragg grating sensor decreases with the increase of the thickness of the intermediate layer.However,as the basis structure is subjected to the bending moment,the thickness of the interlayer has greatly affected on the dynamic strain transfer rate,the dynamic strain transfer rate of the FBG increases with the augment of the thickness of the intermediate layer.