Research On Optic Fiber High Temperature Strain Sensor And Strain Transfer Law

Such as the temperature and strain monitoring of aerospace engine blades,the temperature and strain change greatly,and the cross-sensitivity between them will cause errors in the measurement results.Optical fiber F-P interference structures and fiber Bragg gratings(FBG)have been widely used in the fields of fiber sensing.The dual-parameter sensor based on these two structures is a good method to monitor the temperature and strain parameters.Nowadays,the common applications for strain detection are civil engineering,aerospace,and other fields.The central idea of strain monitoring for fiber optic sensors is to effectively transfer the deformation of the external matrix to the fiber.During the transmission of strain from the substrate to the optical fiber,the strain measured by the optical fiber sensor will be less than the true strain of the substrate structure.In order to make the measured value of the sensor equal to the real strain value of the base structure as much as possible,the transmission mechanism between the base structure and the fiber-optic sensor must be explored in detail to obtain an accurate strain transfer coefficient,thereby correcting the measurement result.In some specific environments.The work of this thesis is mainly divided into two parts: stress transfer analysis of three-layer embedded optical fiber structure and real-time monitoring of strain under high temperature environment.the main work is as followed:Two kinds of optical fiber high temperature strain sensors based on F-P cascaded FBG structure are designed.A thermal regeneration grating is obtained by annealing the femtosecond laser-engraved grating,and a temperature-strain dual-parameter sensor is fabricated by cascading a single mode fiber-hollow core fiber-single mode fiber F-P interference structure.The simultaneous measurement of 0-1000?? strain in high temperature environment from 20? to 1000? is realized.The root mean square errors of the sensor are 0.441?? and 1.037?,respectively,and the condition number of the sensitivity characteristic matrix is 9.55.The designed sensor has good strain repeatability.An adhesive method using corundum tube and high temperature glue was proposed for encapsulation and sensitization.A new fiber-optic sensor structure is designed,which isolates the problem of temperature and strain being sensitive to the crossover of the F-P interference structure and the thermal regeneration grating at the same time.It realizes accurate distinguished measurement of temperature and strain,and improves the strain sensitivity of the sensor.The experimental results show that the designed sensor can beapplied to the simultaneous measurement of 0-450?? strain in the temperature environment of 20? to 1000?.Establish the stress transfer model of the embedded three-layer optical fiber structure,and derive the stress transmission coefficient of the embedded three-layer structure;Analyzed the stress transfer relationship between the matrix structure and the high temperature glue and optical fiber;The influence of the physical properties of the high-temperature glue and the matrix on the average strain transfer rate was studied,and the stress transfer simulation was carried out using finite element analysis.