페라이트강의 동적변형시효 거동에 미치는 기하학적 불연속부의 영향 평가

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Ferritic steels are commonly used as a piping material of nuclear power plant (NPP). It is known that dynamic strain aging (DSA) for ferritic steels occurs in the range 150∼350oC, which includes operating temperature of NPPs. DSA causes an abnormal behavior of material properties; increasing tensile strength and decreasing ductility and toughness of materials at a certain range of temperature. Also, the temperature region of DSA strongly depends on strain rate applied to material, and the mechanical properties are sensitively changed by strain rate at a given temperature. It is important to understand the characteristics of DSA because DSA is a cause of uncertainty in the integrity evaluation of ferritic steel piping components. In particular, it is necessary to clarify the effect of geometrical discontinuity on the DSA behavior of material, since the geometrical discontinuity changes stress and strain states and strain rate in the local region of structure. Therefore, the objective of this study is to investigate the effect of different stress state induced by geometrical discontinuity on DSA behavior of ferritic steels. For this purpose, the present study performed a series of tensile tests using notched-bar specimens including standard tensile specimen under three different displacement rates and various temperatures and evaluated the DSA characteristics of material as a function of notch radius of specimen. ASTM A106 Gr.B carbon steel, which is commonly used as a piping material of nuclear power plant, was used in the experiment. The results of tensile test on the standard specimen showed that DSA phenomena of A106 Gr.B piping material appear in the temperature range 125∼230oC under quasi-static loading rate. The DSA region of A106 Gr.B was moved to higher temperature, about 50∼90oC, when the loading rate increased about 100 times compared to quasi-static loading rate. Also, it was indicated that the notch of specimen moves DSA region of material toward higher temperature under the same displacement rate. Finite element analysis showed that the primary notch effect on the DSA behavior of material is an increase in the strain rate by notch.
Alternative Title
Evaluation of Geometrical Discontinuity Effects on the Behavior of Dynamic Strain Aging in Ferritic Steels
Alternative Author(s)
Lee Sa Yong
조선대학교 대학원
일반대학원 원자력공학과
Awarded Date
Table Of Contents
제 1 장 서 론 1
제 2 장 인장시험 5
제 1 절 재료 및 시편 5
제 2 절 시험조건 5
제 3 절 시험장치 및 절차 6
제 3 장 인장시험 결과 10
제 1 절 표준 인장시험 결과 10
1. 하중-변위 곡선 10
2. 항복강도와 인장강도의 온도 및 변위속도 의존성 10
3. 연신율의 온도 및 변위속도 의존성 11
4. A106 Gr.B 탄소강 배관재의 DSA특성 12
제 2 절 노치 인장시험 결과 12
1. 하중-변위 곡선 13
2. 최대하중의 온도 및 변위속도 의존성 14
3. 연신율의 온도 및 변위속도 의존성 15
4. 노치시편에서 DSA 거동 분석 16
제 3 절 인장 파면 특성 18
제 4 장 노치시편에 대한 응력 및 변형률 상태 분석 36
제 1 절 유한요소모델 36
제 2 절 유한요소시뮬레이션 검증 37
제 3 절 시편형상에 따른 변형 거동 37
1. 응력상태 37
2. 변형률 분포 38
3. 등가 소성변형률 속도 분포 39
제 4 절 DSA거동에 미치는 노치부의 응력 및 변형률 상태 41
제 5 장 결 론 51
참고문헌 53
조선대학교 대학원
이사용. (2013). 페라이트강의 동적변형시효 거동에 미치는 기하학적 불연속부의 영향 평가.
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General Graduate School > 3. Theses(Master)
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