Distributed Optical Fiber Monitoring For Impact And Fatigue Crack Propagation Of Spacecraft Metal Structures

With the increasingly complex and harsh service environment of aerospace vehicles,in the long-term service process,due to the impact,fatigue and other adverse factors,inevitably cause structural deterioration and damage,thus endangering the operational safety and service life of the structure,so it is very important to monitor and evaluate its structural health.Fiber Bragg Grating Sensor(FBG)has many unique advantages,such as light weight,anti-electromagnetic interference,high sensitivity and easy distributed networking.It is very suitable for aerospace applications in complex environment.In this paper,the impact and fatigue crack growth monitoring method of spacecraft aluminium alloy metal structure based on fiber Bragg grating sensor is studied.The main work includes the following aspects:Firstly,according to the application requirement of distributed fiber Bragg grating transmission monitoring system in spacecraft structural health monitoring,a distributed fiber Bragg grating monitoring system based on through-cabin connector and optical switch is studied.In order to evaluate the transmission performance of FBG demodulation system embedded in cabin-piercing connector,the self-repairing method of failure sensor networks based on different spacecraft structures is studied,which provides technical support for the subsequent construction of spacecraft structural health monitoring system.Secondly,taking aluminium alloy cylinder structure as the research object,the optimal configuration and shock response characteristics of fiber Bragg grating sensor in cylinder structure are studied,and a method of shock signal pre-processing using fractal filtering and wavelet decomposition is proposed.On this basis,combined with the wavelet packet decomposition technology,a shock location method based on the energy ratio of the frequency band of the wavelet packet and the intersection of three lines is proposed.The fast and effective identification of the low-speed impact load of the cylindrical structure is realized by using the idea of "first region,then coordinate".Thirdly,the unilateral notched aluminium alloy specimens are selected as the research object.By means of Abaqus finite element simulation technology,the distribution characteristics of strain field corresponding to fatigue crack growth process and the relationship between strain response and crack growth are studied,and the layout of FBG sensors is optimized.On this basis,the relationship between the center wavelength offset and the fatigue crack length of the optical fiber FBG sensor is studied.A mathematical model for predicting the fatigue crack length is established to predict the fatigue crack growth length of the aluminum alloy structure.Finally,according to the requirement of real-time monitoring of impact and fatigue of aircraft and spacecraft in service,using LabVIEW graphical software,human-computer interaction monitoring,data processing and visualization display function modules are designed respectively to realize impact load location and fatigue crack growth monitoring of typical structures based on FBG sensors.