Strain Measurement Method Of High Temperature Structure Based On Fiber Grating

At present,with the flying speed of various types of high-speed aircraft faster and faster,the thermal protection problems caused by the harsh aerodynamic environment has become one of the difficult problems that restrict the development of high-speed aircraft.Thermal-mechanical response characteristics of thermal protection structures in high temperature environment are the foundation of thermal protection design for aircraft,but the current level of high-temperature sensor testing technology can not accurately test the responses.This paper based on ultrahigh temperature ceramics and silicon nitride ceramics,experimental research on high temperature connection method and sensing characteristics of quartz chemical composition grating sensors has been carried out.Based on the characteristics of response caused by strain and temperature of bare grating,the influence of temperature on sensitivity coefficient of strain and sensitivity coefficient of temperature is determined.The wavelength signal is demodulated by the method of temperature compensation,and the separation of the strain wavelength signal and the temperature wavelength signal is realized.The influence of the thickness,length and width of the adhesive layer on the strain transmission is analyzed by using the theoretical model of the matrix-adhesive layer-bare fiber.According to the different thickness of the adhesive layer,the stress distribution at the interface between the adhesive layer and the structure is numerically simulated,the stress concentration at the interface is further reduced by fining the edges of the adhesive layer,and the shape setting mould was designed and prepared according to the section shape of the adhesive layer.Then,Adhesive curing process has been researched by observing the pattern of the solidified colloid and the bonding effect between the colloid and the structure,the optimal method of high temperature grating connection is given.The high temperature sensing system of fiber Bragg grating is established,the high temperature response tests of ultrahigh temperature ceramics and silicon nitride ceramics are carried out,and the stability and accuracy of strain sensing test a re analyzed.In ultrahigh temperature ceramics,the maximum sensing temperature of fiber Bragg grating is 1094.1℃,the coefficient of variation of relative increment of wavelength caused by strain is not greater than 6.0%.The strain measurement error of fiber Bragg grating on ultrahigh temperature ceramics is not more than 10.7%,the strain transfer coefficient is between 0.893~0.984.On silicon nitride ceramics,the maximum sensing temperature of fiber Bragg grating is 1087.2℃,the coefficient of variation of relative increment of wavelength caused by strain is not greater than 15.5%,and with the increase of temperature the coefficient of variation show a decreasing trend.The strain measurement error of fiber Bragg grating is no more than 18.5%,the strain transfer coefficient is between 0.815~0.969.