고온 700℃ 및 상온에서 Type 316L 스테인리스강의 저사이클 피로 성질 데이터의 통계적 변동성 = Statistical Variability of Low-Cycle Fatigue Properties Data of Type 316L Stainless Steel at High-Temperature 700℃ and Room Temperature

다국어 초록 (Multilingual Abstract)

Type 316L austenitic stainless steel is a promising material for various industrial applications, ranging from the nuclear power industry to the marine industry, because of its excellent mechanical properties and high corrosion resistance. Owing to its excellent manufacturing and weldability, it has been widely used in the broad temperature range from cryogenic to high temperatures and under various use operating conditions. Low-cycle fatigue (LCF) is one of the common loading conditions that structural members experience during use. Understanding the material properties that affect service performance, particularly cyclic deformation response behavior, is important for life design and structural integrity evaluation. So, many researchers have investigated the LCF behaviors and cyclic deformation mechanism of Type 316L stainless steel. Most of these studies were conducted over the temperature range of -196 to 650℃ in the uniaxial tension–compression loading mode. However, it is well recognized that scatter inevitably exists in LCF behavior and the fatigue life. Understanding the statistical variability of LCF properties data is crucial for the reliability and safety of structural members subjected to cyclic loading. However, there are few studies that systematically examined the statistical variability of the LCF properties data for hot-rolled Type 316L stainless steel. The main objective of this study is to investigate the cyclic stress response behavior and the statistical variability of the LCF properties data of Type 316L stainless steel at a high temperature of 700℃ and room temperature (RT). In this study, fully reversed strain-controlled LCF tests of hot-rolled Type 316L austenitic stainless steel were carefully conducted with a constant strain amplitude of ±0.5% under a constant strain rate of 1×10-3/s at 700℃ and a constant strain amplitude of ±0.4% under a constant strain rate of 4×10-3/s at RT. The experimental results for 700℃ showed that cyclic stress response behavior for all the test samples showed an initial cyclic hardening behavior, followed by a saturation area for a certain period of time, and then fractured after cyclic softening. Tensile stress, compressive stress, and stress range in one cycle showed coefficients of variation (COV) of 5, 7, and 5%, respectively. Tensile stress, compressive stress, and stress range in half-life cycle showed COV within approximately 2%, and plastic and elastic strain ranges showed COV of 3% and 6%, respectively. The COV of the elastic modulus,  ,  and  were 34, 15 and 28%, respectively. The COV of the fatigue life was 10.6%. The experimental results for RT showed that cyclic stress response behavior showed an initial cyclic hardening behavior, followed by remarkable softening behavior and then fractured after small secondary hardening. The COV for LCF properties data, such as tensile stress, compressive stress, stress range, and elastic modulus in the 1st and half-life cycles, was 0.7%-6.2%. However, the COV of the fatigue life was 20%. It was found that fatigue life had greater scatter than other LCF properties data. Additionally, the fatigue life for 700℃ and RT followed well two-parameter Weibull distribution. The estimated shape and scale parameters for 700℃ and RT were obtained 10.09 and 897 and 6.12 and 8471, respectively.

목차 (Table of Contents)

• 제1장 서 론 1
• 1.1 연구 배경 및 목적 1
• 1.2 연구의 범위 및 방법 5
• 제2장 이론적 배경 6
• 2.1 Type 316L 스테인리스강 6
• 2.1.1 Type 316L 스테인리스강의 역사와 개발 배경 6
• 2.1.2 Type 316L의 기계적 및 물리적 성질과 활용 분야 9
• 2.2 피로 11
• 2.2.1 피로의 개념과 정의 11
• 2.2.2 피로 연구의 역사 14
• 2.2.3 피로해석 및 접근법 19
• 2.2.4 피로의 통계적 변동성 25
• 2.2.5 피로수명 및 피로성질 데이터의 통계적 해석법 30
• 제3장 고온 700℃에서의 저사이클 피로 특성의 통계적 변동성 33
• 3.1 재료 및 시험편 제작 33
• 3.1.1 재료 33
• 3.1.2 시험편 제작 36
• 3.2 실험방법 및 절차 39
• 3.3 실험결과 및 고찰 44
• 3.3.1 반복 응력 반응 거동 44
• 3.3.2 측정량의 통계적 성질 48
• 3.3.2.1 피로수명의 통계적 변동성 55
• 3.3.2.2 첫 번째 사이클의 측정량의 통계적 변동성 57
• 3.3.2.3 반수명에서의 측정량의 통계적 변동성 62
• 3.3.2.4 피로수명의 확률분포 67
• 3.4 결 언 71
• 제4장 상온에서의 저사이클 피로 특성의 통계적 변동성 73
• 4.1 재료 및 시험편 제작 73
• 4.1.1 재료 73
• 4.1.2 시험편 제작 74
• 4.2 실험방법 및 절차 75
• 4.3 실험결과 및 고찰 78
• 4.3.1 반복 응력 반응 거동 78
• 4.3.2 측정량의 통계적 성질 81
• 4.3.2.1 피로수명의 통계적 변동성 84
• 4.3.2.2 첫 번째 사이클의 측정량의 통계적 변동성 86
• 4.3.2.3 반수명에서의 측정량의 통계적 변동성 90
• 4.3.2.4 피로수명의 확률분포 94
• 4.4 결 언 96
• 제5장 고온 700℃ 및 상온에서의 비교 고찰 98
• 제6장 결론 101
• 참고문헌 102
• 감사의 글 114