Research On Fiber Bragg Grating Based Aeronautical Structural Damage Monitoring

The damage of aircraft structures can be detected and identified in the early stage by taking structural health monitoring(SHM)method.The aeronautical SHM plays an important role in ensuring structural safety,guiding aircrafts maintenance and extending aircrafts life.Due to the small size,light weight anti-electromagnetic interference and easy networking,fiber Bragg gratings(FBG)are promising sensors in aeronautical SHM applications in recent years.The FBG based aeronautical structural health monitoring system and damage identification methods are studied in this thesis.The main research contents and creative contributions of the thesis are described as follows:1.The sensing mechanism of fiber Bragg grating is studied.The deformation of the reflection spectrum in the typical non-uniform strain field is calculated.The characteristics related to the reflection spectrum deformation are extracted.The relationship between reflection spectrum deformation and non-uniform strain field changes are established.2.The miniaturized fiber grating interrogation system based on volume phase grating is studied.A four-way fiber grating interrogation system is designed by taking wavelength division multiplexing and time division multiplexing methods.The hardware and software of the interrogation system is studied,the system performance indices are tested.3.The damage identification method based on structural state vector is proposed.The fiber Bragg grating sensors array based structural damage monitoring on aeronautical composite complex structure is studied.The sensors array is arranged on the carbon fiber reinforced composite stiffening plate.The multi-directional strain of the structure under loading state is measured and the state vector is established for damage identification.4.A quantitative method for crack propagation based on multi characteristics of fiber Bragg grating reflective intensity spectrum is proposed.The relationship between the crack propagation length and the fiber grating reflective spectral deformation is studied by theoretical and finite element methods.The crack propagation length is monitored using the characteristics of reflective spectra.The reflective spectral characteristics of apodized and uniform fiber Bragg gratings are compared by taking the experiment on the central-hole-edged crack structure.The result of crack propagation monitoring experiment shows that comparing with the apodized Bragg grating,the uniform Bragg grating has higher sensitivity on crack propagation monitoring.