單秋成臺灣大學：機械工程學研究所江家慶Chiang, Chia-ChinChia-ChinChiang2007-11-282018-06-282007-11-282018-06-282005http://ntur.lib.ntu.edu.tw//handle/246246/61424Carbon fiber reinforced plastics (CFRP) are used in various fields due to their high specific strength and specific modulus. It is important to monitor the damage occurrence and development to make CFRP materials reliable and safe. Current methods for internal defect examination in polymeric composites are time consuming and often cannot provide real time monitoring while the components concerned are in use. We propose to use optical fiber sensors for real time monitoring of internal defect development under fatigue loading. Optical fiber has a small diameter, is unaffected by electro-magnetic interference and is reasonably temperature resistant. It may be embedded inside a composite material and comes close to the internal defects. The current work aimed at exploring the use of embedded fiber Bragg grating (FBG) to monitor fatigue damage evolution in a Graphite/Epoxy composite. The on-set and development of the fatigue damage was assessed through changes in the shape of the optical spectrum and shift in wavelengths in the optical fiber sensors. The evolution in light spectrum during fatigue may be divided into four stages. The test specimens were also examined using X-ray radiography, ultrasonic scan, modulus degradation and optical microscopy to reveal the type and extents of the defects at different stages of fatigue damage. Comparison with conventional examination results shows that changes in the light spectrum are associated with (1) matrix cracking in the 90o lamina; (2)splitting along the fiber direction in the ±45o laminae; (3) splitting along the fiber direction in the 0o lamina ; and (4) delamination. As a conclusion, embedded fiber grating sensors appears to have the potential to be developed into a useful tool for on-line structural health monitoring of composite structures.Content Abstract I List of Figures III List of Acronyms VIII Chapter 1 Introduction 1 Thesis layout 2 Chapter 2 Background 3 2.1 Basic of optical fibers 3 2.1.1 Introduction to optical fibers 3 2.1.2 Types of fiber 3 2.1.3 Basic parameters of optical fibers 4 2.2 Optic fiber grating sensors 5 2.2.1 Fiber Bragg grating (FBG) 6 2.2.2 Fabrication of fiber Bragg grating sensors 7 2.2.3 Introduction to long period fiber grating 7 2.2.4 Fabrication of long period fiber grating 9 2.3 Fatigue damage in composite materials 9 2.4 Embedded FBG in composite materials 11 2.4.1 Embedded FBGs for curing monitoring and residual strain measurement in composite. 11 2.4.2 Comparison the embedded FBGs with traditional internal defects detection method in composite materials 12 2.4.3 Damage monitoring by embedded FBGs in composite materials 12 2.5 Summary 14 Chapter 3 Theory of optic fiber grating sensors and interrogation system 23 3.1 Theory of optic fiber grating sensors 23 3.1.1 Theory of FBG 23 3.1.2 Theory of LPFG 27 3.2 Optic fiber grating sensors interrogation system 29 3.2.1 Working principle of the current intensity modulation method for FBG interrogation 31 3.2.2 Working principle of the current intensity modulation method for LPFG interrogation 32 3.2.3 Comparison of different interrogation methods 32 Chapter 4 Experimental procedure 39 4.1 Fabrication of optic fiber sensors: 39 4.1.1 Fabrication fiber Bragg grating sensors 39 4.1.2 Fabrication of Long period fiber grating 39 4.2 Application of optical fiber grating sensors to different measurements 40 4.2.1 Strain monitoring 40 4.2.2 Temperature calibration 41 4.2.3 High frequency strain monitoring 41 4.2.4 Crack closure measurement 41 4.3 Preparation of composite materials 42 4.3.1 Composite laminate 42 4.3.2 Embedding FBG in composite laminate 43 4.3.3 Fatigue test of composite materials with embedded FBGs 43 4.4 Damage evaluation methods 44 4.4.1 Optical Microscopy 44 4.4.2 C-scan method 44 4.4.3 X-radiation method 45 Chapter 5 Optical fiber grating sensors 53 5.1 Quasi-steady state characterizations of optical fiber grating sensors 53 5.1.1 Quasi-steady Temperature measurement 53 5.1.2 Quasi-steady Strain measurement 54 5.1.3 Environmental index effect 54 5.1.4 Comparison of fiber grating sensors 56 5.2 The hybrid FBG-LPFG intensity modulation sensing system for FBG sensor interrogation. 57 5.2.1 Intensity modulation method for FBG interrogation 57 5.2.2 FBG as dynamic strain sensor under cyclic loading 57 5.2.3 FBG as dynamic strain sensor under high frequency loading 58 5.2.4 Application: crack closure measurement by FBGs sensors 60 5.3 The hybrid FBG-LPFG intensity modulation sensing system for LPFG sensor interrogation. 62 5.3.1 Temperature measurement of SC-LPFG and DC-LPFG by intensity modulation system 62 5.3.2 LPFG as dynamic strain sensor under cyclic loading 63 5.4 Summary: 64 Chapter 6 Fatigue damage monitoring in composite laminate 77 6.1 Experiment plan 77 6.2 Group A: Fatigue damage mechanism evaluation 78 6.3 Group B: Monitoring of fatigue damage development 79 6.4 In-depth Fatigue damage mechanism evaluation (Groups C~D): 83 6.4.1 Monitoring of the emergence of fatigue damage in composite 84 6.4.2 Spectra evolution with damage development 85 6.4.3 Comparison with other methodology of damage evaluated 87 6.5 Summary 89 Chapter7 Conclusions and future work 122 7.1 Conclusions for OFGS and interrogation System 122 7.2 Conclusion for embedded FBGs for fatigue damage monitoring 122 7.2 Future work 125 Reference 127 Author Biography 1347979880 bytesapplication/pdfen-US布拉格光柵長週期光柵能量調變複合材料疲勞損傷Fiber Bragg GratingLong Period Fiber GratingIntensity ModulationCompositeFatigue Damagethesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/61424/1/ntu-94-D89522023-1.pdf