Research On Stress Measurement Of Thin-walled Structure Based On Optical Frequency Domain Reflection Technology

Thin-walled structures are widely present in the aerospace and other manufacturing fields.Changes in the external environment are likely to cause damage to the thin-walled structures,thereby damaging the instruments and equipment in the structure.Therefore,the stress monitoring of thin-walled structures is critical.Traditional discrete sensing technology has been unable to monitor the stress field of the entire thin-walled structure;with the continuous development of distributed sensing technology,optical fiber is a distributed sensor with excellent performance in both academic and industrial circles.It has been widely researched and applied.Compared with traditional sensors,fiber optic sensors can measure a variety of different physical quantities along the entire line through a single fiber,and the measurement range is wider and the measurement accuracy is higher.By applying fiber-optic sensors to the stress monitoring of thin-walled structures,distributed real-time monitoring of the stress state can be achieved,so that structural fatigue can be pre-warned in advance,structural damage can be prevented,and the safety and reliability of the system can be improved.Therefore,this paper starts the research of distributed optical fiber sensor stress measurement system based on optical frequency domain reflection technology(OFDR),and builds the system,and conducts stress test experiment on the thin-walled structure.The research content and research results of this article are as follows:1.By comparing different stress test methods,the OFDR technology based on optical fiber is adopted.Using the sensitivity of optical fiber to stress,a simplified model of fiber-thin-wall structure is established.Through stress analysis,the stress transfer characteristics of the external response to fiber-thin-wall structure are obtained.Using ANSYS software to carry out static simulation of the fiber-thin-wall structure,under different constraints and load conditions,the simulation results of stress magnitude are obtained.2.Designed the overall plan of the OFDR test system,and completed the system construction work.By comparing the direct optical detection methods,the advantages of optical heterodyne detection and the influencing factors of key parameters are analyzed.Aiming at the nonlinear sweeping tuning effect of the light source,the method of hardware compensation is used to realize the linear sweeping of the light source.Based on the principle of Mach-Zehnder interferometer,the optical path including the main interferometer and the auxiliary interferometer is designed and constructed.The beat frequency signal obtained by the auxiliary interferometer is used as the acquisition card to trigger the external clock signal;Transform and inverse transform,use cross-correlation arithmetic to process the data.3.The stress test experiment was carried out by the OFDR system built by myself,and the verification test was carried out using the OBR4600 backlight reflectometer.Through the photoelectric converter and the data acquisition card,the data of the beat signal in the main interferometer and the auxiliary interferometer are obtained,and the algorithm is written in MATLAB to analyze the data in the frequency domain,and the relevant micro-strain data is obtained.Using the OFDR system built by myself and the OBR4600 backlight reflectometer to perform strain position measurement and stress magnitude test,the actual test results are compared with the simulation results in Chapter 2 to verify the feasibility of the system solution;further obtained micro strain and weight The relationship curve of the quality,based on the test result of the OBR4600 backlight reflectometer,is a analysis of the cause of the measurement error of the built system.