Research On High Temperature Strain Sensing Technology Based On EFPI And Regenerated Fiber Bragg Grating

Strain measurement in high temperature such as the field of aircraft and petrochemical industry has always been a research hotspot.Different from the conventional environment,the strain monitoring of large-scale equipment in aerospace and other high-temperature areas is often intensive and the measuring system is complex.At the same time,the high temperature environment will bring many impacts on sensors and measuring instruments.Optical fiber sensor with the advantages of being small size,lightweight,multiplexing capability and immunity to electromagnetic interference has received extensive attention in structural health monitoring,and it also has broad application prospects in high temperature strain monitoring of large structures.However,Fabry-Perot interferometer sensors(F-P)and Fiber Bragg gratings(FBG),which are commonly used for strain measurement,have temperature-strain cross-sensitivity,limited measurement range,and the strength decrease in high temperature and other issues have greatly limited the development of fiber-optic sensing technology in high temperature field.Therefore,it is of great significance to study the strain measurement and large-strain measurement based on optical fiber sensing technology under high-temperature environment.Based on the above background,an “extrinsic F-P/regenerated FBG”(EFPI/RFBG)composite sensor is proposed to measure the temperature and strain simultaneously in high temperature.The prepared sensor has the advantages of large strain measurement range and high application temperature.The main research work and achievements of this thesis are as follows.First of all,the current situation of research on Extrinsic F-P Interferometer(EFPI)strain sensor,high temperature FBG temperature sensor and EFPI and FBG multiplex sensor at home and abroad are investigated.We analyzed and summarized predecessors' researches,therefore we decided that the research project was the study of EFPI/RFBG hybrid sensor which is used in high temperature and large strain measurements on large structures.Secondly,because of the decline of conventional FBG in high temperature environment,the high temperature resistant RFBG is used as the temperature compensation element in the composite sensor.The formation mechanism of RFBG and the method of improving its reflection intensity were analyzed.The related researches on temperature sensing characteristics,wavelength repeatability,wavelength and light intensity decay characteristics of RFBG were carried out.After 4 thermal annealing cycles from 18°C to 1000°C,the error of the wavelength of RFBG is 3pm,and the long-term stability error at wavelength of 1000°C is only 2.2pm.Finally,a large strain-range EFPI/RFBG hybrid sensor was designed and its strain sensing characteristics under normal temperature and high temperature environment were tested.The temperature measurement error of the sensor is only 0.67%,and the maximum measured strain value is 17448.6??.The accuracy of the measurement is verified by finite element analysis.At the same time,the EFPI/RFBG hybrid sensing system was used to test the thermal structure of large-scale composite materials,and the feasibility of the sensor engineering application was verified.