單秋成臺灣大學:機械工程學研究所楊仕偉Yang, Shi-WeiShi-WeiYang2010-06-302018-06-282010-06-302018-06-282009U0001-0408200910201900http://ntur.lib.ntu.edu.tw//handle/246246/187216Carbon Fiber Reinforced Plastic (CFRP) composites used today are at the leading edge of materials technology, with performance and fair costs to the applications. It is important to detect the impact fractures inside CFRP, preventing the structure from catastrophic failure. Due to its tiny size, Fiber Bragg Grating (FBG) sensors can be embedded inside the CFRP materials without significantly affecting its intensity. The purpose of this study was to discuss the feasibility of investigating impact damage by using pre-embedded FBGs in CFRP materials. Just after impact, the FBG sensor could detect the impact damage if it is in the vicinity of the impact source. For impact at a distance from the sensor, bending test was conducted to observe the relation between the peak wavelength shift and bending load charts to reveal any hysteresis phenomenon on the peak wavelength-bending load charts that could help us to infer the impact damage up to 50mm away from the sensors. For the post-impact fatigue test, it was found the characteristic Bragg wavelength gradually became buried in a wide band of wavelengths. In order words, the FBG lost its capability to act as a sensor. It was found that this phenomenon may be attributed to the highly non-uniform strain inside the CFRP specimen near the impact position induced by a combination of fatigue and impact damages. This revealed a previously undocumented phenomenon that may limit the application of FBG in damage monitoring inside composite material.口試委員審定書 Icknowledgments IIbstract IIIontents IVist of Figure VIist of Table XIhapter 1 Introduction 1.1 Background 1.2 Motivation 2.3 Methodology 3.4 Thesis layout 4hapter 2 Literature Review 5.1 Fiber grating sensors 5.1.1 Introduction of fiber grating sensors 5.1.2 The properties of fiber Bragg grating sensors 7.1.3 Fabrication of fiber Bragg grating sensors 11.2 Embedded FBG in composite materials 12.2.1 Thermal residual stress in composite materials 12.2.2 Birefringence effect 14.2.3 Sensitivity of embedded FBG sensors 15.2.4 Damage monitoring by embedded FBG sensors in composite materials 15.3 Impact and Fatigue damage in composite materials 16.3.1 Impact damage in composite materials 16.3.2 Fatigue damage in composite materials 17hapter 3 Experimental instruments and methodology 26.1 Experimental instruments 26.2 Experimental procedure of impact test 31.2.1 Fabrication of fiber Bragg grating sensors 31.2.2 Preparation of CFRP plate specimens 32.2.3 Embedding FBG sensors in specimens for impact test 32.2.4 Experimental procedure for impact test 33.3 Experimental procedure of post-impact fatigue test 35.3.1 Preparation of specimens for post-impact fatigue test 35.3.2 Embedding FBG sensors in specimens for post-impact fatigue test 36.3.3 Experimental procedure for post-impact fatigue test 36hapter 4 Results and discussion 52.1 Embedded FBGs in CFRP composite 52.2 Impact on the FBGs (R=0mm) 53.2.1 R=0mm, H=80mm 53.2.2 R=0mm, H=140mm 54.2.3 Micrographs of impact-damaged CFRP specimen 54.3 Impact at 30mm from FBGs (R=30mm) 55.3.1 R=30mm, H=80cm 55.3.2 R=30mm, H=140cm 59.4 Impact at 50mm from FBGs (R=50mm) 61.4.1 R=50mm, H=80cm 61.4.2 R=50mm, H=140cm 62.5 Quantification of drift distance in peak wavelength lines 63.6 Results of post-impact fatigue test for impact position B 67.7 Results of post-impact fatigue test for impact position A and C 70.8 Result of fatigue without impact 72hapter 5 Conclusions and future work 118.1 Impact damage monitoring 118.2 post-impact fatigue damage monitoring 119.3 Future works 120eferences 122ppendix 125ist of Figure ig. 2-1: Reflective and transmitted spectra of the Single-mode fiber Bragg gratings [2] 18ig. 2-2: (a) The fiber Bragg grating sensor is under a uniaxial stress, and (b) a general non-uniaxial stress. [2] 18ig. 2-3: Reflective spectra of FBGs under non-uniform strain fields [2] 19ig. 2-4: A simple situation where the strain distribution is piecewise-uniform over the lengths L1 and L2 of the FBG sensors. [2] 19ig. 2-5: Temperature variation induced Bragg wavelength shift [11] 20ig. 2-6: Bulk interferometer method: UV interferometer for writing Bragg Gratings in optical fibers. [10] 20ig. 2-7: Phase mask method to fabricate FBG [14] 21ig. 2-8: Scheme for the explanation to the residual stress of composite manufacture [2] 21ig. 2-9: Reflection spectra from the uncoated normal FBG sensor, which was embedded into the CFRP laminate, measured during the cure cycle (a) heating process (b) cooling process [16] 22ig. 2-10: FBG response along mechanical test: (a) tensile test (b) flexural test [18] 23ig. 2-11: Evaluation of delamination size. (a) Definition of intensities for two peaks and (b) logarithmic curves of intensity ratio against delamination size [20] 24ig. 2-12: Schematic failure mechanisms for fiber reinforced composites: (a) matrix cracking (b) fiber breakage (c) fiber/matrix interface debonding (d) delamination [21] 24ig. 2-13: Schematic fatigue damage modes of quasi-isotropic composite laminate [21] 25ig. 3-1: Optical spectrum analyzer (MS9710C) 38ig. 3-2: MTS 810 material testing system 38ig. 3-3: Impact test machine 39ig. 3-4: Configuration of the impact test machine [26] 39ig. 3-5: Iron falling dart (Left) used in impact test and Aluminum falling dart (Right) used in post-impact fatigue test 40ig. 3-6: Configuration of the four-points bending instrument 40ig. 3-7: Broadband light source 41ig. 3-8: Abrasive diamond-coated wheel cutting machine 41ig. 3-9: Hot press molding system 42ig. 3-10: Ultrasonic imaging system 42ig. 3-11: Schematic of the C-Scan for laminate damage evaluation [21] 43ig. 3-12: Fusion splicer 43ig. 3-13: Optical cleaver 44ig. 3-14: Optical cleaver 44ig 3-15: Schematic of the diaphragm type forming mold for laminate curing process 44ig. 3-16: The conditions for laminate curing process 45ig. 3-17: Schematic of fiber-embedded method and laminates stacking sequence 45ig. 3-18: Configuration of embedded FBGs in CFRP plate specimen 46ig. 3-19: Experimental procedure flow diagram for impact test 46ig. 3-20: Schematic of Impact distance R and Impact positions A0, A45, and A90 47ig. 3-21: Schematic of experimental setup in bending test 47ig. 3-22: Bending test was conducted in different directions for measuring embedded FBG sensors in each layer. (a) For measuring the FBGs in L2 and L3 (b) For measuring the FBGs in L1 and L4 48ig. 3-23: Configuration of test specimen for post-impact fatigue test 48ig. 3-24: Experimental procedure flow diagram for post-impact fatigue test 49ig. 3-25: Schematic of experimental setup in post-impact fatigue test 49ig. 3-26: Schematic of Impact positions A (in the upstream of the gratings based on the route of the light propagation), B (the center of the specimen), and C (in the downstream of the gratings based on the route of the light propagation). 50ig. 4-1: Comparison of FBG spectra before embedding and after curing. (a) Before embedding (b) After curing. 77ig. 4-2: Energy exchange between two peaks due to birefringence effect. (a) Initial state of the fiber (b) On bending 77ig. 4-3 (a)-(d): Comparison of spectra from FBG sensors in each layer between before and after impact under a 80cm drop-height.(a) Embedded in L1 (b) Embedded in L2 (c) Embedded in L3 (d) Embedded in L4 78ig. 4-4: Comparison of spectra from FBG sensors in each layer between before and after impact under a 140cm drop-height. (a) Embedded in L1 (b) Embedded in L2 (c) Embedded in L3 (d) Embedded in L4 79ig. 4-5: Optical Micrographs of the impact-damaged specimen (drop height 80cm) [32] 80ig. 4-6: Optical Micrographs of the impact-damaged specimen (drop height 140cm) [32] 80ig. 4-7: Comparison of spectra from FBG sensors in L1 and L2 between before and after impact under a 140cm drop-height. 81ig. 4-8: The shifts in wavelength of the spectra from the embedded FBG sensor in L4 before and after impact under 80cm drop height. (a) Before impact (b) After impact at the three impact positions 82ig. 4-9: The shifts in wavelength of the spectra from the embedded FBG sensor in L1 before and after impact under 80cm drop height. (a) Before impact (b) After impact at the three impact positions 83ig. 4-10 (a): Wavelength shifts from the embedded FBG sensors in L1 and L2 along the bending test before impact. 84ig. 4-10 (b): Wavelength shifts from the embedded FBG sensors in L3 and L4 along the bending test before impact. 85ig. 4-11 (a): Comparison of wavelength shifts from embedded FBG sensor in L1 along a bending test before and after impact under an 80cm drop-height and a distance 30mm away from FBG sensors. 86ig. 4-11 (b): Comparison of wavelength shifts from embedded FBG sensor in L2 along bending test before and after impact under an 80cm drop height and a distance 30mm away from FBG sensors. 87ig. 4-11 (c): Comparison of wavelength shifts from embedded FBG sensor in L3 along bending test before and after impact under an 80cm drop height and a distance 30mm away from FBG 88ig. 4-11 (d): Comparison of wavelength shifts from embedded FBG sensor in L4 before and after impact under an 80cm drop height and a distance 30mm away from FBG sensors. 89ig. 4-12 (a): Comparison of wavelength shifts from embedded FBGs in L1 and L2 before and after impact under an 140 cm drop-height and a distance 30mm away from FBG sensors. 90ig. 4-12 (b): Comparison ofwavelength shifts from embedded FBGs in L3 and L4 before and after impact under a 140cm drop-height and a distance 30mm away from FBG sensors. 91ig. 4-13: Comparison of Ultrasonic C-scan images between before and after impact under a 80cm drop height and a distance 30mm from the FBG sensors. (a) Before impact (b) After impact at A0, A45, and A90. 92ig. 4-14: Comparison of Ultrasonic C-scan images between before and after impact under a 140cm drop-height and a distance 30mm from the FBG sensors. (a) Before impact (b) After impact at A0, A45, and A90. 92ig. 4-15 (a): Comparison of wavelength shifts from embedded FBG sensor in L1 along a bending test before and after impact under an 80cm drop height and a distance 50mm away from 93ig. 4-15 (b): Comparison of wavelength shifts from embedded FBG sensor in L2 along a bending test before and after impact under an 80cm drop height and a distance 50mm away from FBG sensors. 94ig. 4-15 (c): Comparison of wavelength shifts from embedded FBG sensor in L3 along a bending test before and after impact under an 80cm drop height and a distance 50mm away from FBG sensors. 95ig. 4-15 (d): Comparison of wavelength shifts from embedded FBG sensor in L4 along a bending test before and after impact under a140cm drop height and a distance 50mm away from FBG sensors. 96ig. 4-16 (a): Comparison of wavelength shifts from embedded FBGs in L1 and L2 before and after impact under a 140cm drop height and a distance 50mm away from FBG sensors. 97ig. 4-16 (b): Comparison of wavelength shifts from embedded FBGs in L3 and L4 before and after impact under a 140cm drop height and a distance 50mm away from FBG sensors. 98ig. 4-17: Comparison of Ultrasonic C-scan images between before and after impact under an 80cm drop-height and a distance 50mm from the FBG sensors. (a) Before impact (b) After impact at A0, A45, and A90 99ig. 4-18: Comparison of Ultrasonic C-scan images between before and after impact under a 140cm drop-height and a distance 50mm from the FBG sensors. (a) Before impact (b) After impact at A0, A45, and A90 99ig. 4-19: Quantitative evaluation of the average drift distance of peak wavelength lines by RMSD. 100ig. 4-20: Spectra changes from embedded FBG in L1 with various fatigue cycles under an 80cm drop height and impact at position B 100ig. 4-21: Spectra changes from embedded FBG in L4 with various fatigue cycles under an 80cm drop height and impact at position B 101ig. 4-22: Spectra changes from embedded FBG in L1 with various fatigue cycles under a 140cm drop height and impact at position B 101ig. 4-23: Spectra changes from embedded FBG in L4 with various fatigue cycles under a 140cm drop height and impact at position B 102ig. 4-24: Comparison of Ultrasonic C-scan images between 0 fatigue cycle and 200000 fatigue cycles after impact at the center of specimen (position B):(a) 140cm drop-height (b) 80cm drop-height 102ig. 4-25: Optical micrographs on the sectional view of the post-impact fatigued specimen (H=140cm, impact position B, 200000 cycles). 103ig. 4-26: Spectra changes from embedded FBG in L1 with various fatigue cycles under a 140cm drop-height and impact at position A 104ig. 4-27: Spectra changes from embedded FBG in L4 with various fatigue cycles under a 140cm drop-height and impact at position A 104ig. 4-28: Spectra changes from embedded FBG in L1 with various fatigue cycles under a 140cm drop-height and impact at position C 105ig. 4-29: Spectra changes from embedded FBG in L4 with various fatigue cycles under a 140cm drop-height and impact at position C 105ig. 4-30: Comparison of Ultrasonic C-scan images between 0 fatigue cycle and 200000 fatigue cycles after impact under a 140cm drop-height and impact at position A and B: (a) Impact position C (downstream of the gratings) (b) Impact position A (upstream of the gratings) 106ig. 4-31: Spectra changes from embedded FBG in L1 with various fatigue cycles without impact. 106ig. 4-32: Spectra changes from embedded FBG in L4 with various fatigue cycles without impact. 107ig. 4-33: Optical micrographs of the same FBG in L1 as the one whose spectra are shown in Fig 4-20. (a) Focus on fiber surface (b) Focus on cladding 107ig. 4-34: Optical micrographs of the same FBG in L2 as the one whose spectra are shown in Fig 4-21. (a) Focus on fiber surface (b) Focus on cladding 108ig. 4-35: Comparisons of spectra before and after the FBG was drawn out from the specimens, conducted the post-impact fatigue test. (a) The FBG is the same as the one whose spectra is shown in Fig 4-20 (b) The FBG the same as the one whose spectra is shown in Fig 4-21 108ig. 4-36: Schematic of experimental set-up in bending test for the FBG drawn out from CFRP specimen. 109ig. 4-37: Reflection spectra from the FBG, which is the same as the one whose spectra shown in Fig 4-20, after drawn out from CFRP specimen at various strains 109ig. 4-38: Comparisons of spectra before and after submerging the specimen which had been conducted post-impact test in acetone. (a) Spectra from the FBG embedded in L1 (b) Spectra from the FBG embedded in L4 110ig. 4-39: Reflection spectra from the FBG embedded in CFRP specimen along the tensile test at various strains. 110ig. 4-40: Reflection spectrum at the strain 5126μ in Fig. 4-38 in the wavelength span from 1520nm to 1580nm 111ig. 4-41: Reflection spectrum at the strain 8031μ in Fig. 4-38 in the wavelength span from 1555nm to 1561nm 111ig. 4-42: Spectrum of intensity increasing in other wavelength in the span from 1400nm to 1700nm. 112ist of Tableable 3.1: Impact energies from different drop heights and dart masses 51able 3.2: Experimental parameters in impact test 51able 4.1: Average drift distance in peak wavelength from the FBG in L1 under experimental parameters of different impact distances and drop heights. 113able 4.2: Average drift distance in peak wavelength from the FBG in L2 under experimental parameters of different impact distances and drop heights. 114able 4.3: Average drift distance in peak wavelength from the FBG in L3 under experimental parameters of different impact distances and drop heights. 115able 4.4: Average drift distance in peak wavelength from the FBG in L4 under experimental parameters of different impact distances and drop heights 116able 4.5: Differences of drift distances in peak wavelength between before impact and after impact at all positions. 117en-US布拉格光纖光柵碳纖維複合材料衝擊損傷衝擊後疲勞損傷Fiber Bragg GratingCarbon Fiber Reinforced PlasticImpact damagePost-impact fatigue damage.thesis