표제지
목차
Nomenclature 12
Abbreviation 14
Abstract 15
제1장 서론 19
1.1. 연구 배경 및 목적 19
1.2. 논문 구성 25
제2장 관련 이론 26
2.1. 고온용 금속재료 26
2.2. 무시할 수 있는 크리프 36
2.3. 저사이클 피로 및 크리프-피로 거동 40
2.3.1. 변형률-수명 접근방법 44
2.3.2. 저사이클 피로수명 평가 49
2.4. 연구 동향 55
제3장 Type 316L(N) 강의 무시할 수 있는 크리프 평가 및 해석 60
3.1. 연구 배경 60
3.2. TNEC 곡선 생성을 위한 계산 절차[이미지참조] 63
3.3. 결과 및 고찰 66
3.3.1. 크리프 수명예측식 66
3.3.2. 크리프 수명예측식의 적용 결과 69
3.3.3. 무시할 수 있는 크리프(TNEC) 곡선 도출 결과[이미지참조] 82
3.3.4. 무시할 수 있는 크리프(TNEC) 곡선의 참조응력 의존성[이미지참조] 87
3.3.5. Type 304 및 Type 316계 강과 TNEC 곡선 비교[이미지참조] 93
3.4. 결론 96
제4장 Alloy 800H의 크리프-피로 거동 97
4.1. 연구 배경 97
4.2. 시험 재료 및 방법 98
4.3. 결과 및 고찰 104
4.3.1. 반복 응력 반응 거동 104
4.3.2. 인장 피크 응력과 압축 밸리 응력의 비교 111
4.3.3. 반복 응력-변형률 반응 거동 115
4.3.4. 피로수명에 미치는 온도의 영향 119
4.3.5. 파면 분석을 통한 피로 파괴 기구 122
4.4. 결론 127
제5장 총결론 128
참고 문헌 130
Table 2-1. Comparison of chemical composition of Type 316, 316L, and 316L(N) stainless steel 34
Table 2-2. Comparison of chemical composition of Alloy 800, 800H, and 800HT 35
Table 2-3. Maximum temperature limit for various materials in ASME Code 39
Table 3-1. Reference stress and creep strain criteion in several high-temperature design codes 65
Table 3-2. Expected minimum stress-to-rupture values for Type 316L(N) Stainless steel 81
Table 3-3. Calculated (a)reference stresses and (b)creep strength (a) Calculated Rp02(moy) to 650℃[이미지참조] 83
Table 4-1. Chemical composition of Alloy 800H used in this work 101
Table 4-2. Mechanical properties of Alloy 800H at temperature of 700, 750 and 800℃ 101
Table 4-3. Test conditions of CF and LCF 102
Fig. 1-1. Operation temperature in fuel cell system 20
Fig. 1-2. Photos of damage in fuel cell combustor piping 21
Fig. 2-1. Operating conditions of SOFCs 28
Fig. 2-2. Conceptual diagram of nuclear hydrogen production system used by Gen IV VHTR 29
Fig. 2-3. Main components and candidate materials of VHTR 30
Fig. 2-4. Description of negligible creep curve 38
Fig. 2-5. Comparison of low cycle fatigue (LCF) and high cycle fatigue (HCF) 41
Fig. 2-6. Concept of the local strain-life approach 42
Fig. 2-7. Schematic of a typical strain cycle for a component operating in VHTR 43
Fig. 2-8. Hysteresis loop 46
Fig. 2-9. Cyclic hardening (a) constant strain amplitude, (b) stress response (increasing stress level) and (c) cyclic stress-strain response 48
Fig. 2-10. Cyclic softening (a) constant strain amplitude, (b) stress response (decreasing stress level) and (c) cyclic stress-strain response 48
Fig. 2-11. Schematic diagram of strain-life curve 51
Fig. 2-12. Elastic and plastic strain energy density under cyclic loading 54
Fig. 2-13. Chart of literature review in this study 59
Fig. 3-1. Flow chart for evaluation related to integrity prediction of high-temperature and high-pressure components 62
Fig. 3-2. Creep rupture data of Type 316L(N) steel 71
Fig. 3-3. Fitting a master curve to derive optimal constant C values 72
Fig. 3-4. Optimal correlation coefficient at C=27 for Type 316L(N) steel 73
Fig. 3-5. A master curve obtained by LMP 74
Fig. 3-6. Results of creep life prediction by LMP method 75
Fig. 3-7. Fitting a master curve to derive optimal activation energy values of WE model 76
Fig. 3-8. Optimal correlation coefficient at Q=330kJ/mol for Type 316L(N) steel by WE model 77
Fig. 3-9. Optimal master curve of WE model 78
Fig. 3-10. Results of creep life prediction obtained by WE model 79
Fig. 3-11. Comparison of creep life prediction by WE model and RCC-MRx code 80
Fig. 3-12. Plot of creep rupture properties and yield strengths corrected by reference stress using average yield strength and creep... 85
Fig. 3-13. Comparison of predicted TNEC curve and RCC-MRx Code[이미지참조] 86
Fig. 3-14. Plot of creep rupture properties and yield strengths corrected by reference stress using average yield strength and creep SCF for... 89
Fig. 3-15. Plot of creep rupture properties and yield strengths corrected by reference stress using minimum yield strength and creep SCF... 90
Fig. 3-16. Plot of creep rupture properties and yield strengths corrected by reference stress using maximum allowable strength and creep... 91
Fig. 3-17. Comparison of TNEC curves obtained from different reference stress for Type 316L(N) steel[이미지참조] 92
Fig. 3-18. Comparison of TNEC curves for Type 304, 316L, and 316L(N) steels given in RCC-MRx[이미지참조] 94
Fig. 3-19. Comparison of TNEC curves collected through literature survey for Type 304 and 316 series[이미지참조] 95
Fig. 4-1. Shape and dimension of CF testing specimen 99
Fig. 4-2. Testing machine and extensometer used in this study (a) material testing machine (model: MTS 370), (b) low cycle fatigue test and... 100
Fig. 4-3. Waveforms of total-strain controlled LCF and CF tests 103
Fig. 4-4. Comparison of evolution of peak tensile and valley compressive stresses as a function of number of cycles between creep-fatigue... 107
Fig. 4-5. Comparison of evolution of stress amplitude as a function of number of cycles between creep-fatigue and low cycle fatigue at... 109
Fig. 4-6. Comparison of degree of hardening as a function of temperature between creep-fatigue and low cycle fatigue at total strain range... 110
Fig. 4-7. Comparison of tensile peak stress and compressive valley stress as a function of number of cycles at 700℃: (a) LCF experiment; (b) CF experiment 112
Fig. 4-8. Comparison of tensile peak stress and compressive valley stress as a function of number of cycles at 750℃: (a) LCF experiment; (b) CF experiment 113
Fig. 4-9. Comparison of tensile peak stress and compressive valley stress as a function of number of cycles at 800℃: (a) LCF experiment; (b) CF experiment 114
Fig. 4-10. Comparison of stress-strain hysteresis loops of Alloy 800H at 700℃ and total strain range of 0.6% for first cycle and half-life 116
Fig. 4-11. Comparison of stress-strain hysteresis loops of Alloy 800h at 750℃ and total strain range of 0.6% for first cycle and half-life 117
Fig. 4-12. Comparison of stress-strain hysteresis loops of Alloy 800h at 800℃ and total strain range of 0.6% for first cycle and half-life 118
Fig. 4-13. Peak/valley stresses as a function of number of cycles, the fatigue life and the crack initiation life for LCF and CF 121
Fig. 4-14. Microscopic mechanism by low cycle fatigue at 750℃ 123
Fig. 4-15. Surface cracking observed by optical microscope for LCF at 750℃, 0.6% 124
Fig. 4-16. Microscopic mechanism by CF at 750℃ 126