표제지
목차
인용부호 12
Abstract 14
1. 서론 16
1.1. 연구 배경 16
1.2. 구조물 변형과 파손 해석 18
1.2.1. 파괴역학 18
1.2.2. 복합재료 22
1.2.3. 연료전지 26
1.3. 파괴 평가 수법 28
1.3.1. 평가 수법 28
1.3.2. 스펙클 패턴(speckle pattern) 30
1.4. 연구의 목적 33
2. 배경 이론 35
2.1. DIC 35
2.1.1. DIC 특징 35
2.1.2. DIC 이론 및 평가방법 36
2.2. 균열 측정 평가수법 45
2.2.1. GLCM 45
2.2.2. ACDM 46
3. 실험 설계 및 방법 53
3.1. 시험편 53
3.1.1. 스펙클 패턴 형성 및 황동 시험편 53
3.1.2. CFRP 하이브리드 복합재 57
3.1.3. 고체연료전지 62
3.2. 실험방법 65
3.2.1. 인장실험 65
3.2.2. 3점 굽힘실험 68
3.2.3. 4점 굽힘실험 70
4. 결과 및 고찰 78
4.1. DIC 스펙클 형상에 따른 영향 평가 78
4.1.1. 스펙클 패턴 농도에 따른 GLCM평가 78
4.1.2. 인장실험 결과 81
4.1.3. 미소균열 측정 평가 85
4.1.4. 소결 90
4.2. 탄소섬유 복합재료의 균열 측정 91
4.2.1. 노치가 없는 시험편의 균열 발생 91
4.2.2. 초기 균열 시험편의 균열진전 평가 94
4.2.3. 시험편 적층 방향의 영향 98
4.2.4. 소결 103
4.3. 고온환경에서 연료전지 계면 균열 측정 평가 104
4.3.1. 실험온도에 따른 하중 및 균열 발생 평가 104
4.3.2. 고온상태의 고체산화물 연료전지 전극측 계면에서의 DIC평가 108
4.3.3. Ag 페이스트에 대한 SEM 분석결과 113
4.3.4. ACDM 균열진전평가 115
4.3.5. 소결 118
5. 결론 119
참고문헌 122
Table. 1. Cross-correlation and sum-of-squared-differences criterion. 42
Table. 2. Physical properties of Brass. 54
Table. 3. Physical properties of CFRP and Al alloy. 57
Table. 4. The crack length measurement from ACDM and Image J. 117
Fig. 1. Fail safety and inspection design curve. 21
Fig. 2. Type of composite material. 23
Fig. 3. Schematic of correlation analysis in reference(undeformed) and deformed subsets. 37
Fig. 4. Example of GLCM calculation at 4 × 4 pixel image fragment and its GLCM and normalization. 39
Fig. 5. Automated crack detection and measurement theory. 50
Fig. 6. The skeletonize process. 52
Fig. 7. Adoption of skeletonize in crack image. 52
Fig. 8. The dimension of specimen and ROI for DIC. 54
Fig. 9. The random speckle patterns in accordance with the density. 56
Fig. 10. The type of laminated Al/CFRP composite. 59
Fig. 11. The geometry of 3 point bending specimen. 60
Fig. 12. The DIC pattern around the initial notch crack. 61
Fig. 13. The geometry of SOFC specimen. 63
Fig. 14. The manufacturing process of the SOFC specimen. 64
Fig. 15. DIC film analysis process and equipment. 66
Fig. 16. Tensile test specimen. 67
Fig. 17. The apparatus of the flexural loading test with a CCD camera for DIC analysis. 69
Fig. 18. The halogen heat control system. 72
Fig. 19. The apparatus of the 4 point-loading test with CCD camera and a halogen heat system. 73
Fig. 20. A DIC pattern around the notch crack. 74
Fig. 21. The silicon stamp for micro crack speckle pattern. 76
Fig. 22. The gray level of the speckle pattern on the surface of the SOFC. 77
Fig. 23. The variation of the contrast by GLCM evaluation according to the density of gray level. 79
Fig. 24. The variation of the entropy by GLCM evaluation according to the density of gray level. 80
Fig. 25. The captured images and distributed histogram of 3 kinds of speckle patterns by 0-255 the gray level of the density((a)... 82
Fig. 26. The stress-strain curves by DIC evaluation under 3 kinds of different gray level density of speckle patterns. 83
Fig. 27. The comparison of the elastic modulus of between DIC and strain gage measurement. 84
Fig. 28. A microscope DIC pattern at a SENT specimen. 86
Fig. 29. The relationship of the force and displacement at the SENT specimen for a micro crack estimation by DIC. 87
Fig. 30. The strain contours in y direction by DIC evaluation on the SENT specimen at each loading step. 88
Fig. 31. The variation of strain according to the distance from the notch tip at each loading step. 89
Fig. 32. The flexural loading and displacement curve without an initial notch crack(NN specimen). 92
Fig. 33. The strain contours of NN specimen. 93
Fig. 34. The flexural loading and displacement curve with an initial notch crack(1 mm length, T1 sequence). 95
Fig. 35. The strain variation accompanying crack propagation from an initial crack(length 1 mm, T1). 96
Fig. 36. The variation of the strain at the crack tip. 97
Fig. 37. The flexural loading and displacement curve with an initial notch crack(1 mm length, T2 sequence). 99
Fig. 38. Displacement comparison of T1 and T2 Test Specimens(1 mm length, T1 & T2 sequence). 100
Fig. 39. The strain variation accompanying crack propagation from an initial crack(length 1 mm and time interval 2 sec, T2). 101
Fig. 40. The variation of the strain according to the crack extension. 102
Fig. 41. The 4 point-bending load-displacement curves with an initial notch crack(0.03 mm length) at 20℃, 500℃, 700℃. 105
Fig. 42. The images of crack propagation from initial at a notch crack. 107
Fig. 43. The strain accompanying crack propagation at (a) 700℃, (b) 500℃ and (c) 20℃. 109
Fig. 44. The variation of displacement and strain in Ag paste layer (0.03 mm thickness along 1a to 1b direction, (a) 20℃. 110
Fig. 45. The variation of displacement and strain in Ag paste layer (0.03 mm thickness along 1a to 1b direction, (b) 500℃. 111
Fig. 46. The variation of displacement and strain in Ag paste layer (0.03 mm thickness along 1a to 1b direction, (c) 700℃. 112
Fig. 47. The Ag paste SEM image. 114
Fig. 48. The crack behavior evaluation by ACDM method. 116