U-노치 및 균열을 갖는 보의 응력집중계수 및 응력확대계수

서보성(Bo Seong Seo),이광호(Kwang Ho Lee) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.5

단순보와 외팔보의 U-노치 및 균열에 대한 응력집중계수 및 응력확대계수를 유한요소법 및 광탄성실험에 의해 해석하였다. 해석결과를 사용하여 응력집중계수 및 응력확대계수의 추정 그래프를 얻었다. 노치의 응력집중계수해석을 위하여 무차원 노치 길이 H(시편의 높이)/h=1.1~2, 무차원 틈 간격 r(노치선단의 반경)/h=0.1~0.5로 하였다. 여기서 h=H-c, c=노치길이이다. 해석결과 틈 길이가 증가할수록 그리고 틈 간격이 좁아질수록 응력집중계수는 증가 한다. 응력집중계수는 단순보가 외팔보다 더 크게 나타나나, 실제 일정한 하중과 노치길이 및 틈 간격 하에서 최대 응력값은 단순보보다 외팔보에서 크게 발생함을 알 수 있었다. 균열해석을 위하여 무차원 균열길이 α(균열길이)/H=0.2~0.5로 하였다. 균열의 길이가 증가 할수록 무차원 응력확대계수는 증가한다. 일정한 하중과 일정한 균열길이하에 응력확대계수 값은 단순보 보다 외팔보에서 크게 발생함을 알 수 있었다. The stress concentration factors and stress intensity factors for a simple beam and a cantilever are analyzed by using finite element method and phtoelasticity. Using the analyzed results, the estimated graphs on stress concentration factors and stress intensity factors are obtained. To analyze stress concentration factors of notch, the dimensionless notch length H(height of specimen)/h=1.1~2 and dimensionless gap space r(radius at the notch tip)/h=0.1~0.5 are used. where h=H-c and c is the notch length. As the notch gap length increases and the gap decreases, the stress concentration factors increase. Stress concentration factors of a simple beam are greater than those of a cantilever beam. However, actually, the maximum stress values under a load, a notch length and a gap occur more greatly in the cantilever beam than in the simple beam. To analyze stress intensity factors, the normalized crack length α(crack length)/H=0.2~0.5 is used. As the length of the crack increases, the normalized stress intensity factors increase. The stress intensity factors under a constant load and a crack length occur more greatly in the cantilever beam than in the simple beam.

응력집중계수를 이용한 해상풍력터빈 트라이포드 지지구조물의 신뢰성해석

이상근(Sang Geun Lee),김동현(Dong Hyawn Kim) 한국해안해양공학회 2016 한국해안해양공학회 논문집 Vol.28 No.2

응력집중계수를 이용하여 해상풍력발전기 트라이포드 지지구조물에 대한 신뢰성 해석을 수행하였다. 파랑과 풍하중의 극치분포함수는 POT방법을 사용하여 동적응답을 분석함으로써 추정되었다. 일계신뢰도법을 사용하여 신뢰성해석을 수행하였으며, 한계상태함수는 지지구조물의 이음부에서 발생하는 응력을 기반으로 정의하였다. 보 요소에서 계산된 응력에 응력집중계수를 곱하는 방법과 판 요소를 사용하여 계산하는 두 가지 방법으로 최대응력을 계산하여 신뢰성 해석을 수행하고 결과를 비교 분석하였다. Reliability analysis of tripod support structure for offshore wind turbine was performed. Extreme distribution function of peak response due to wind and wave loads was estimated by applying peak over threshold(POT) method. Then, stress based limit state function was defined by using maximum stress of support structure which was obtained by multiplying beam stress and concentration factor. The reliability analysis result was compared when maximum stress was calculated from shell element. Reliability index was evaluated using first order reliability method(FORM).

적외선 열화상 응력측정법에 의한 동적 응력집중계수 예측

최만용(Man Yong Choi),강기수(Ki Soo Kang),박정학(Jeong Hak Park),안병욱(Byung Wook Ahn),김경석(Koung Suk Kim) Korean Society for Precision Engineering 2008 한국정밀공학회지 Vol.25 No.5

Structural components subjected to high frequency vibrations, such as those used in vibrating parts of gas turbine engines, are usually required to avoid resonance frequencies. Generally, the operating frequency is designed at more than resonance frequencies. When a vibrating structure starts or stops, the structure has to pass through a resonance frequency, which results in large stress concentration. This paper presents the transient thermoelastic stress analysis of vibrating cantilever beam using infrared thermography and finite element method (FEM). In FEM, stress concentration factor at the 2nd resonance vibration mode is calculated by the mode superposition method of ANSYS. In experiment, stress distributions are investigated with infrared thermography and dynamic stress concentration factor is estimated. Experimental result is agreed with FEM result within 10.6 %. The advantage of this technique is a better immunity to contact problem and geometric limitation in stress analysis of small or micro structures.

Hot-spot 응력을 이용한 십자형 필렛 용접재의 피로강도 평가

김대진(Dae-Jin Kim),석창성(Chang-Sung Seok),구재민(Jae-Mean Koo),서정원(Jung-Won Seo),구병춘(Byeong-Choon Goo) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

In this study, fatigue tests to obtain S-N curves and FE analyses to obtain structural stress concentration factors were conducted for the two types of cruciform fillet welded joints, that is, load-carrying and non load-carrying types. Then we changed the obtained S-N curve of load-carrying joint to that based on hot-spot stress. As a result, the S-N curve of load-carrying joint based on hot-spot stress was almost exactly coincided with that of non load-carrying joint based on nominal stress. So we have concluded that the fatigue strength of a welded joint with different geometry from the non load-carrying cruciform joint could be estimated by the structural stress concentration factor obtained by considering the stress distributions along the expected crack path..

원형 KT 연결부의 응력집중계수 평가시 통계적 접근을 통한 용접 비드 형상의 영향도 분석

심기찬,이강수 한국강구조학회 2022 韓國鋼構造學會 論文集 Vol.34 No.3

Tubular members are one of the most frequently used member for offshore structures. It is important to calculate a more accurate stress concentration factor because hot spot stress of welded joint has a great influence on the result of the fatigue analysis. In this study, KT-joint was modelled using 3D solid element and FE analysis was performed. Based on the results, FE model was verified through comparison with experimental data, results in previous studies, classification rule such as DNV. Also, in order to observe the variation of the hot spot stress and stress concentration factor according to the size of welding beads, the numerical analysis with balanced axial loading condition was performed. And the correlation with geometric parameters and weld beads, the effect on stress concentration factor were analyzed and summarized. As a result, it was confirmed that the weld beads should be considered for accurate fatigue life calculation when designing the welded joint of the offshore structure 원형 부재는 연안 구조물에 가장 자주 사용되는 부재 중 하나이며, KT 연결부의 핫스팟 응력은 구조물의 피로수명에 큰 영향을 미치기 때문에 보다 정확한 응력집중계수를 계산하는 것이 중요하다. 본 연구에서는 3차원 솔리드 요소를 이용하여 KT 연결부를모델링하고 유한요소해석을 수행하여 해석결과를 이전 선행연구결과 및 노르웨이 선급규정의 제안식과 비교하여 검증을 수행하였다. 또한 균일압축하중조건하의 연결부 관련 무차원 매개변수 분석과 더불어 용접 비드의 기하학적 형상에 따른 핫스팟 응력 및 응력집중계수의 변화를 관찰하기 위해 매개변수를 변화해가며 수치해석을 수행하였다. 결과적으로 무차원 변수와 용접 비드간 상관관계, 응력집중계수에 대한 영향을 분석하고 정리하였다. 결과적으로 해양구조물의 연결부 설계시 정확한 피로수명 계산을 위해 용접 비드 형상을 고려해야 함을 확인하였다.

가압중수로 압력관 이물질 프레팅 결함의 탄성 응력집중계수 수식 도출

김종성(Jong Sung Kim),오영진(Young Jin Oh) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.2

가동중검사 동안 가압중수로 압력관에서 탐지된 베어링 패드 프레팅 결함, 이물질 프레팅 결함 등 체적결함에 대해서는 CSA N285.8-05 에 따라 탄성 응력집중계수 수식을 이용하여 피로균열 및 수소지연균열이 개시되는 것을 평가하여야 한다. CSA N285.8-05 에는 이물질 프레팅 결함에 대해서는 선형파괴역학 기반한 개략적인 수식만이 제시된다. 본 연구에서는 이러한 이물질 프레팅 결함에 대해 2 차원 유한요소 해석과 일부 수정된 Kinectrics 사의 공학적 절차를 통해 이물질 프레팅 결함의 기하학적 특성이 좀더 상세히 고려된 탄성 응력집중계수 수식을 도출하였다. 도출된 수식을 적용한 결과와 3 차원 유한요소 해석 결과를 비교한 결과, 도출된 수식은 유한요소 해석과 잘 일치하는 결과를 얻을 수 있음을 확인하였다. If volumetric flaws such as bearing pad fretting flaws and debris fretting flaws are detected in the pressure tubes of pressurized heavy water reactors during in-service inspection, the initiation of fatigue cracks and delayed hydrogen cracking from the detected volumetric flaws shall be assessed by using elastic stress concentration factors in accordance with CSA N285.8-05. The CSA N285.8-05 presents only an approximate formula based on linear elastic fracture mechanics for the debris fretting flaw. In this study, an engineering formula considering the geometric characteristics of the debris fretting flaw in detail was derived using two-dimensional finite element analysis and Kinectrics, Inc."s engineering procedure with slight modifications. Comparing the application results obtained using the derived formula with the three-dimensional finite element analysis results, it is found that the results obtained using the derived formula agree well with the results of the finite element analysis.

3차원 경사크랙을 가진 중공축의 응력확대계수산정

이종선,하영민 한국공작기계학회 1999 한국생산제조학회지 Vol.8 No.1

In this study, intensity factors, K_Ⅰ, K_Ⅱ, K_Ⅲ are existing at the same time to a hollow cylindrical bar of three dimension inclination crack. In order to investigate by experimentally the effect of the inclination angle φof crack, artificial inclination cracks in the circumferential direction are put in the surface of a hollow cylindrical bar made by the epoxy-resin. Experimentally, stress analysis methods of stress intensity factors were proposed. But, suitable method are the caustic method and the photoelastic stress freezing method. The mixed mode of K_Ⅰ and K_Ⅱ were determined by the photoelastic method of the classical approach method and the FORTRAN language program of the used smallest square method.

半無限平板의 두 圓孔排列이 應力集中에 미치는 影響

吳世旭(Sae-Wook Oh),朴榮哲(Young-Chul Park),金峻永(Jun-Young Kim) 한국해양공학회 1990 韓國海洋工學會誌 Vol.4 No.1

This study is concerned about the stress concentration factor measurement by photoelastic method, for the case of two circular holes arrangement in 3㎜ semi-infinite plate under tensile load, the ratio of those two circular holes diameter, the ratio of distance apart from circular holes to breadth and the two holes arrangement angle with loading direction were varied.<br/> Besides, the measured stress concentration by photoelastic method around one circular hole was compared with that by strain-gage method.

사각 평판에서 타원의 회전에 따른 응력집중계수의 변화에 관한 연구

김현수(H. S. Kim),최태원(T. W. Choi),최경호(K. H. Choi),박기훈(K. H. Park),권영석(Y. S. Kwon) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.10

Sometimes open holes are required for the function and the weight reduction of structure and machinery. However, the serious stress concentration occurs because of the geometric discontinuity caused by the holes and cutting section. In this study, it is attempted to obtain the stress concentration coefficients of the inner surface of the hole boundary by changing the rotate angle of holes on the homogeneous isotropic plate. And the effects on the plate are investigated. The results show that the stress level becomes low and the distribution area widens the position of stress concentration just at 90˚ as being the angle β increases.

응력집중부를 갖는 표면균열재의 균열길이 변화에 따른 피로거동

남기우(K.W. Nam),김선진(S.J. Kim) 한국해양공학회 1995 韓國海洋工學會誌 Vol.9 No.1

Surface defects in structural members are apt to be origins of fatigue crack growth, which may cause serious failure of whole structures. Most structure has a part where stress concentrates such as welded joints, corner parts, etc. And then, analysis on crack growth and penetration from these defects, therefore, is one of the most important subjects for the reliability of LBB design.<br/> The present paper has performed an experimental and analysis on the fatigue crack propagation by variety in crack length of surface cracked plate with stress concentration part. The crack growth behavior can be explained quantitatively by using Newman-Raju equation and the stress partitioning method proposed by ASME B&P Code Sec. XI.<br/> The stress concentration factor Kt has affected on the crack growth. The crack growth after penetration depends upon the initial front side crack length.