Research On The Temperature,strain And Pressure Monitoring Technology Of Hypersonic Flight Vehicle Surface Based On Optical Fiber Sensing Technology

The technology of hypersonic vehicle is the frontier of aerospace field in the future.It is important to measure temperature,strain and pressure parameters in-stiu and real-time at ultra-high temperature environment for the safe operation of hypersonic vehicle.It is of great significance for the design and performance optimization of hypersonic vehicle to evaluate the temperature distribution,mechanical characteristics and pressure distribution of the thermal protection structure in the ground high temperature test and actual flight vie the high temperature resistant optical fiber sensing technology.Therefore,this paper mainly focuses on the research of hypersonic vehicle surface temperature,strain and pressure sensing based on optical fiber sensing technology.The main research contents are as follows:1.The high temperature sensing characteristics based on Fiber Bragg Grating(FBG)are investigated.Firstly,the mechanism of the FBG including the Bragg condition,induced refractive index modulation and the refrectivity calculation are analyzed.Three type gratings including RFBG,type ? FBG and type ?A FBG are studied.The mechanism of grating formation,writing method and temperature resistance characteristics are analyzed,respectively.The relationship between the central wavelength of FBG and parameters of temperature and strain is analyzed theoretically.The temperature sensing characteristics of RFBGs and type ? fiber gratings are investigated by experiments.The results show that both the regenerated grating and the type ? FBG can meet the requirements of temperature sensing at temperature up to 1000 ?.However,RFBG usually involves hydrogen loading,uncoating and subsequent high-temperature annealing,which reduce the mechanical strength of the RFBG.While type ? FBG does not need the above steps.Compared with Ge-doped-core type ? FBG,pure-silica-core type ? FBG has relatively excellent high-temperature stability at temperature higher than 800 ?.2.The high-temperature strain measurement system of FBG is established.The high temperature strain sensing characteristics of RFBG and type ? FBG are studied experimentally.The experimental results show that both RFBG and type ? FBG can be able to achieve strain measurement below 600 ?.However,when the temperature is higher than 700 ?,the combination of temperature and strain results in the decrease of fiber viscosity.So the wavelength stability of FBG becomes worse.The experimental results demonstrated that high temperature strain performance of pure-quartz-core type ? FBG is better than that of Ge-doped-core type ? FBG.Based on the combination of FBG and the structure under test,the influence of three different packaging methods including surface mounted FBG,substrate FBG and clamped FBG on train transfer efficiency are analyzed and compared.The temperature and strain decoupling technology based on polarization maintaining RFBG is proposed.The temperature and strain measurement simultaneously are realized.3.The sensing theory,structure design and fabrication method of high temperature fiber pressure sensor based on sapphire cavity extrinsic Fabry-Perot interference(EFPI)structure are investigated.The sensing mechanism of pressure sensor and the relationship between the design parameters of sapphire diaphragm and pressure sensitivity are also studied and analyzed.The structure design of extrinsic optical fiber Fabry-Perot interferometric pressure sensor based on sapphire cavity is proposed.The temperature desensitization packaging method based on thermal expansion coefficient difference of between fiber and sapphire is proposed.The fabrication of all sapphire cavity EFPI pressure sensor is realized.4.The corresponding experimental test system is established aim to test the encapsulated optical fiber temperature sensor,surface mounted optical fiber strain sensor and all sapphire cavity optical fiber pressure sensor,respectively.The experimental results demonstrated that FBG temperature sensor encapsulated in pure quartz and corundum ceramic tube could realize the temperature measurement with the upper limit of 1000 ? and accuracy is within ± 3 ?.For surface mounted optical fiber strain sensor,the results of strain measurement are consistent with those of extensometer at 400 ?.A pressure test system for sapphire cavity fiber Fabry-Perot sensor is established.The static pressure sensitivity,resolution and other parameters are tested in the range of room temperature to 800 ?.The experimental results show that it can meet the pressure sensing requirements below 800 ? although the pressure sensitivity decreases with the increase of temperature.