| When fiber Bragg grating sensors(FBG)are used to measure the structural strain,the strain transfer rate is the most direct factor to affect measurement accuracy.Compared with the traditional resistance strain gauge,FBG sensors have a lot of advantages,such as strong resistance to electromagnetic interference,easy to accomplish long distance signal transmission and realize large-scale distributed measurement.Because of these advantages,FBG sensors are widely used in Bridges,aerospace,machine tools and other large-scale and strong electromagnetic fields.Existing transfer rate theories are mostly on the basis of under static load matrix structure.The researches show that process of bond has a great influence of the ability of static transmission of FBG sensors.But dynamic lord is beard to the structure in mostly actual working condition.According to the practical engineering of dynamic strain measurement,this paper takes the FBG sensors as the research object.Based on structural dynamics,a model of FBG sensor dynamic strain transfer is founded.A steady-state expression is deduced according to the sine excitation.Meanwhile,many influencing factors of FBG sensor dynamic strain transfer are discussed,and the laws of them are verified by experiments.The main research contents in this paper include: Firstly,introduces the purpose and significance of the research of FBG strain sensors' dynamic strain transfer law,summarizes the development of surface pasted fiber Bragg grating sensor static strain transfer technology and its dynamic strain measurement technology at home and aboard,and discusses the problems of existing theory when used to measure dynamic strain in actual condition.Then,the kinetics model of surface pasted FBG sensors dynamic strain transfer is established according to structural dynamics.Based on the model,the dynamics equation of the transmission mechanism is deduced.As basal body under sine signal lord for example,the transfer rate of various points along the fiber axial are gotten,as well as the average transfer rate of the bonded length.The influence of the mechanical parameters to average strain transfer rate is analyzed by using MATLAB software.Afterwards,using the transient structural analysis module of ANSYS software,a large number of finite element simulation analysis of the surface bonded FBG sensor dynamic strain transfer model are Accomplished,and the researches of the influence of parameters on the transmission rate are taken to verify the laws' effectiveness in the theoretical calculation.At last,based on American MTS 810 system,a great number of experiments of surface bonded FBG sensors dynamic strain transfer are taken,through the single variable control method,to verify the effectiveness of the laws of theoretical derivation and finite element simulation analysis.The results of theory and experiment shows that the vibration frequency,the length of glue,the thickness of glue and middle layer thickness of glue have a major impact on FBG dynamic strain transfer rate.The width of glue has minor effect on the transfer rate.When the vibration frequency is far less than the structure natural frequency,the dynamic strain transfer rate remain the same through different frequency,its experimental value was 92%.Before the vibration frequency achieve the natural frequency,the transfer rate increases very slowly with the increase of vibration frequency.When the length of glue is more than 2 times of FBG length,the transfer rate was obviously better than the rate of shorter,its experimental value was 92%.FBG strain sensor dynamic strain transfer ratio decreases with increasing the thickness of glue,decreases with increasing middle layer thickness of glue,remains unchanged with increasing width of glue.The conclusions offer a guidance for high precision dynamic strain measurement by surface bonded FBG strain sensors. |
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