Title Page
ABSTRACT
국문 초록
Contents
Nomenclature 19
Chapter 1. INTRODUCTION 21
1.1. Background 21
1.2. Objective 25
1.3. Structure of This Thesis 26
Chapter 2. LITERATURE REVIEW 28
2.1. Introduction 28
2.2. Review of Existing VLCF Evaluation Models 29
2.2.1. Manson-Coffin Law 29
2.2.2. Ductile Damage Parameter 30
2.2.3. Cyclic Void Growth Model 34
Chapter 3. PROPOSED STRAIN-BASED VERY LOW CYCLE FATIGUE EVALUATION MODEL 40
3.1. Introduction 40
3.2. Strain-based Very Low Cycle Fatigue Evaluation Model 42
3.2.1. Assumption of Void Shrinkage Ratio 42
3.2.2. Very Low Cycle Fatigue Evaluation Model Considering Void shrinkage 48
3.3. Application Procedure 50
3.4. Summary and Discussion 55
Chapter 4. APPLICATION TO NOTCHED C(T) TEST DATA 63
4.1. Introduction 63
4.2. Summary of Experiment 65
4.3. Fatigue Evaluation of Notched C(T) Test 70
4.3.1. Determination of Strain-based Very Low Cycle Fatigue Evaluation Model 70
4.3.2. Elastic-Plastic FE Analysis of Notched C(T) Test 73
4.3.3. Fatigue Evaluation Results 76
4.4. Summary and Discussion 81
Chapter 5. Application to Piping Elbow Test Data 101
5.1. Introduction 101
5.2. Summary of Experiment 102
5.3. Fatigue Evaluation of Piping Elbow Test 107
5.3.1. Determination of Strain-based Very Low Cycle Fatigue Evaluation Model 107
5.3.2. Elastic-Plastic FE Analysis of Piping Elbow Test 110
5.3.3. Fatigue Evaluation Results 114
5.4. Summary and Discussion 120
Chapter 6. CONCLUSION AND FUTURE WORK 144
6.1. Conclusion 144
6.2. Future Work 146
REFERENCES 147
Table 3.1. Chemical composition of SA508 Gr.3 low alloy steel and TP316L stainless steel. 57
Table 3.2. Tensile properties of SA508 Gr.3 and TP316L obtained from smooth bar tensile test. 57
Table 3.3. Calculated values of void shrinkage ratio of SA508 Gr.3 at various strain amplitudes. 57
Table 3.4. Calculated values of void shrinkage ratio of TP316L at various strain amplitudes. 58
Table 3.5. Material constants αsl and m₂, presented in [32][이미지참조] 58
Table 4.1. Tensile properties of SA508 Gr.3 low alloy steel and TP316L stainless steel. 83
Table 4.2. Maximum measured values of the CMOD for displacement-controlled notched C(T) tests. 83
Table 4.3. Summary of experimentally measured failure cycle. The value in the parenthesis is the number of load set shown in Table 4.2. 83
Table 4.4. Determined parameters of the Chaboche combined hardening model of SA508 Gr.3 and TP316L. 84
Table 4.5. Comparison of damage increment per cycle according to k value. The value in the parenthesis represents the percentage ratio with... 84
Table 4.6. Comparison of predicted fatigue life with experimental data. 85
Table 4.7. Weight for each load set to calculate the equivalent failure cycle. 85
Table 4.8. Comparison of predicted fatigue life with experimental data. The value in the parenthesis represents the percentage ratio of... 85
Table 5.1. Chemical composition of SA234 WPB carbon steel and SA403 WP316 stainless steel. 122
Table 5.2. Averaged mechanical properties of SA234 WPB carbon steel and SA403 WP316 stainless steel. 122
Table 5.3. Applied displacement amplitudes for each load set in the displacement-controlled elbow bending test. 122
Table 5.4. Summary of elbow cyclic bending test results: failure cycle, failure mode and location. The value in the parenthesis is the number of... 123
Table 5.5. Material properties provide in [32, 65] and determined material constant in Eq. (5.1). 123
Table 5.6. Calculated void shrinkage ratio of SA234 WPB at various strain amplitude. 124
Table 5.7. Calculated void shrinkage ratio of SA403 WP316 at various strain amplitude. 124
Table 5.8. Elastic modulus and bi-linear kinematic hardening model parameters used in elastic-plastic FE analysis of elbow test. 125
Table 5.9. Comparison of predicted failure cycles with experimentally measured failure cycle. 125
Table 5.10. Normalized displacement amplitude and weight for each cycle to calculate the equivalent failure cycle. 125
Table 5.11. Comparison of predicted equivalent failure cycles with experimentally measured failure cycle. The value in the... 126
Fig. 3.1. (a) Dimensions of the smooth bar tensile specimen (unit: mm) and (b) stress-stain curves obtained from tensile test. 59
Fig. 3.2. Best-fit fatigue life curves of low alloy steel and stainless steel in [56]. 60
Fig. 3.3. Variation of void shrinkage ratio with plastic strain range. 60
Fig. 3.4. (a) Effect of tensile and compressive stress on the void size change and (b) variations of the stress triaxiality and load with the equivalent... 61
Fig. 3.5. Variations of stress triaxiality and equivalent plastic strain in one cycle. 62
Fig. 4.1. Dimensions of (a) smooth bar and (b) notched bar tensile specimen. 86
Fig. 4.2. Engineering stress-strain curves obtained from smooth and notched bar tensile test: (a) SA508 Gr.3 and (b) TP316L. 87
Fig. 4.3. Dimensions of the (a) notched 1T C(T) specimen (SA508 Gr.3) and notched 0.5T specimen (TP316L). 88
Fig. 4.4. Schematic diagram of applied CMOD history for notched C(T) test. 89
Fig. 4.5. Experimentally measured maximum and minimum load histories. 89
Fig. 4.6. Photographs of crack initiation at notch tip after test. 90
Fig. 4.7. FE meshes for smooth and notched tensile specimen. 90
Fig. 4.8. True stress-plastic strain curves obtained from smooth bar tensile test. 91
Fig. 4.9. Comparison of engineering stress-strain curves of smooth and notched tensile test with FE simulation results: (a) SA508 Gr.3 and... 92
Fig. 4.10. Variation of the stress triaxiality with equivalent plastic strain: (a) SA508 Gr.3 and (b) TP316L. 93
Fig. 4.11. Multi-axial fracture strain loci for SA508 Gr.3 and TP316L. 94
Fig. 4.12. Void shrinkage ratio for SA508 Gr.3 and TP316L. 94
Fig. 4.13. 3-D FE meshes of the notched C(T) specimen: (a) 1T specimen and (b) 0.5T specimen. 95
Fig. 4.14. Comparison of FE load history results of notched C(T) test using kinematic hardening model with experimental data of SA508 Gr.3 96
Fig. 4.15. Comparison of FE load history results of notched C(T) test using kinematic hardening model with experimental data of TP316L. 96
Fig. 4.16. Effect of isotropic hardening parameters on FE analysis results of TP316L notched C(T) test: (a) the effect of Q and (b) the effect of b. 97
Fig. 4.17. Variation of the plastic strain range with the number of cycles: (a) SA508 Gr.3 and (b) TP316L. 98
Fig. 4.18. Variation of the void shrinkage ratio with the number of cycles of notched C(T) test: (a) SA508 Gr.3 and (b) TP316L. 99
Fig. 4.19. Effect of the void shrinkage ratio on the cumulated damage of notched C(T) test: (a) SA508 Gr.3 and (b) TP316L. 100
Fig. 5.1. Dimensions of the smooth bar tensile test specimen. 127
Fig. 5.2. Engineering stress-strain curves obtained from smooth and notched bar tensile test: (a) SA234 WPB and (b) SA403 WP316. 128
Fig. 5.3. The elbow specimen with dimensions and test boundary conditions. 129
Fig. 5.4. Schematic diagram of applied displacement history in elbow cyclic bending test. 129
Fig. 5.5. Experimentally obtained load history of elbow specimen: (a) SA234, (b) WP316 Sch. 40 and (c) WP316 Sch. 160. 130
Fig. 5.6. Photograph of elbow specimen after very low cycle fatigue test: (a) SA234 WPB Sch. 40, (b) SA403 WP316 Sch. 40 and (c) Sch. 160. 131
Fig. 5.7. Multi-axial fracture strain loci for SA234 WPB and SA403 WP316. 133
Fig. 5.8. Void shrinkage ratio for SA234 WPB and SA403 WP316. 133
Fig. 5.9. Typical FE model and boundary condition for the pipe elbow simulation. 134
Fig. 5.10. The method to determine bi-linear kinematic hardening model from true stress-stain curve, provided in JSME CC. 134
Fig. 5.11. Comparison of stress-strain curves of bi-linear kinematic hardening model with experimental data: (a) SA234 WPB and (b) SA403 WP316. 135
Fig. 5.12. Comparison of FE analysis results of elbow test with experimental data: (a) SA234 WPB Sch. 40, (b) SA403 WP316 Sch. 40 and (c)... 136
Fig. 5.13. Comparison of cumulated damage histories at intrados, extrados and crown of Sch. 40 elbows: (a) SA234 WPB and (b) SA403 WP316. 138
Fig. 5.14. Comparison of cumulated damage histories at intrados, extrados and crown of SA403 WP316 Sch. 160 elbows: (a) P=0.2 MPa and (b)... 139
Fig. 5.15. Comparison of principal stress components at failure location: (a) Sch. 40 elbow and (b) Sch. 160 elbow. 140
Fig. 5.16. Equivalent plastic strain distribution in the central section of elbow specimens: (a) Sch. 40 elbow and (b) Sch. 160 elbow. 141
Fig. 5.17. Schematic illustration of deformation patterns of elbow under in-plane bending: (a) closing bending and (b) opening bending. 142
Fig. 5.18. Comparison of ovality of Sch. 40 and Sch. 160 elbows with number of cycles. 143