Research On Cryogenic Characteristics Of FBG And Thermal Properties Monitoring Of Composite Structural

With the diversified development of aerospace composite structure to be large-scale,complex and multi-task,it will inevitably be affected by many complex environmental factors during its service life,which will lead to a significant decline in structural reliability.The structural health of the aerospace composite is closely related to its thermal load response characteristics.Therefore,in this paper,the monitoring methods of temperature,thermal strain and thermal properties of typical aerospace composite structures are studied based on optical fiber sensing technology,providing the basis for structural service safety assessment.The main work includes the following aspects:Firstly,the sensing mechanism of fiber Bragg grating(FBG)is analyzed theoretically,and the response spectrum characteristics of FBG sensor under different temperature and strain are studied from numerical simulation and experiments.The formation mechanism of low temperature chirp effect of FBG is studied and validated.Secondly,a package method of tube FBG temperature sensor is proposed.According to the different working conditions,a bunch of tube type FBG temperature sensor is researched.On this basis,the temperature sensing characteristics of FBG sensors in different packages are explored.Thidly,the carbon fiber cylindrical structure and the carbon fiber solid rod structure are selected as the research objects.The thermal strain testing system of the composite structure based on distributed FBG sensor network is constructed.And the errors of FBG sensor and strain gauge in thermal strain monitoring of the structure are analyzed.Then,a carbon fiber honeycomb clamp structure thermal load test system was built to study the reflection spectrum response characteristics of FBG implanted in different layers under high and low thermal loads.A method of calculating the thermal expansion coefficient of the composite plate structure is proposed,which is based on the mechanical model of surface-mount FBG,and the feasibility of the method is verified by numerical simulation.Finally,the hardware test system of FBG in LabVIEW is built.The function requirements and frameworks of the system are proposed.And the main program of the system is designed and completed.At the same time,the design of the man-machine interface is completed.