• 대한기계학회논문집A
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• 제28권7호
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• pp.1014-1020
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• 2004

The present work complies the elastic stress concentration factor for a pipe with local wall thinning, based on detailed three-dimensional elastic FE analysis. To cover practically interesting cases, a wide range of pipe and defect geometries are considered, and both internal pressure and global bending are considered. Resulting values of stress concentration factors are tabulated for practical use, and the effect of relevant parameters such as pipe and defect geometries on stress concentration factors are discussed. The present results would provide valuable information to estimate fatigue damage of the pipe with local wall thinning under high cycle fatigue.

• 한국공작기계학회논문집
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• 제13권4호
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• pp.73-78
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• 2004

The conventional SLT(Shear Lag Theory) which has been proven that it can not provide sufficiently accurate strengthening predictions in elastic regime when the fiber aspect ratio is small. This paper is an extented work to improve it by modifying the load transfer mechanism called NSLT(New Shear Lag Theory), which takes into account the stress transfer across the fiber ends and the SCF(Stress Concentration Factor) that exists in the matrix regions near the fiber ends. The key point of the model development is to determine the major controlling factor among the material and geometrical coefficients. It is found that the most affecting factor is the fiber/matrix elastic modulus ratio. It is also found that the proposed model gives a good result that has the capability to correctly predict the elastic properties such as interfacial shear stresses and local stress variations in the small fiber aspect ratio regime.

• 한국지반공학회논문집
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• 제18권5호
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• pp.133-141
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• 2002

암반파괴의 가장 큰 영향을 미치는 인장강도는 등방의 암석과 횡등방의 암석의 경우는 분명히 다를 것이다. 본 논문에서는 일축압축강도시험에서 횡등방 암석의 탄성정수를 구하고, 간접인장강도시험을 통하여 횡등방 암석의 인장강도와 인장파괴 거동을 분석하였다. 일축압축시험에서 구한 이방성 탄성정수와 간접인장강도시험에서 얻어진 변형률로 시료중앙의 응력집중계수를 구하여, 등방으로 가정하여 구한 인장강도 값과 이방성일때의 인장강도 값을 비교 분석하였다. 실험 결과 횡등방성 암석의 응력집중계수는 층리면의 각도에 따라서 등방재료의 응력집중계수와는 크거나 작은 값을 나타내었다. 횡등방 암석의 인장강도 산정시 등방의 응력집중계수를 사용하는 것은 층리면이 이루는 각도에 따라 인장강도의 과대 혹은 과소 평가됨을 알 수 있었다.

• Structural Engineering and Mechanics
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• 제36권6호
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• pp.669-678
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• 2010

In general means, the stress concentration problem of elastic plate with a rectangular hole can be investigated by numerical methods, and only approximative results are derived. This paper deduces an analytical study of the stress concentration due to a rectangular hole in an elastic plate under bending loads. Base on classical elasticity theory and FEM applying the U-transformation technique, the uncoupled governing equations with 3-DOF are established, and the analytical displacement solutions of the finite element equations are derived in series form or double integral form. Therefore, the stress concentration factor can then be discussed easily and conveniently. For the plate subjected to unidirectional bending loads, the non-conforming plate bending element with four nodes and 12-DOF is taken as examples to demonstrate the application of the proposed method. The inner force distribution is obtained. The solutions are adequate for the condition when the hole is far away from the edges and the thin plate subjected to any transverse loadings.

• 한국생산제조학회지
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• 제6권3호
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• pp.58-64
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• 1997

A micromechanics model to describe the elastic behavior of fiber or whisker reinforced metal matrix composites was developed and the stress concentrations between reinforcements were investigated using the modified shear lag model with the comparison of finite element analysis (FEA). The rationale is based on the replacement of the matrix between fiber ends with the fictitious fiber to maintain the compatibility of displacement and traction. It was found that the new model gives a good agreement with FEA results in the small fiber aspect ratio regime as well as that in the large fiber aspect ratio regime. By the calculation of the present model, stress concentration factor in the matrix and the composite elastic modulus were predicted accurately. Some important factors affecting stress concentrations, such as fiber volume fraction, fiber aspect ratio, end gap size, and modulus ratio, were also discussed.

• 한국공작기계학회논문집
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• 제12권4호
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• pp.63-69
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• 2003

In discontinuous composite mechanics, shear lag theory is one of the most popular model because of its simplicity and accuracy. However, it does not provide sufficiently accurate strengthening predictions in elastic regime then the fiber aspect ratio is small. This is due to its neglect of stress transfer across the fiber ends and the stress concentrations that exist in the matrix regions near the fiber ends. To overcome this shortcoming, a more simplified shear lag model introducing the stress concentration factor which is a function of several variables, such as the modulus ratio, the fiber volume fraction, the fiber aspect ratio, is proposed. It is found that the modulus ratio($E_f$/$E_m$) is the essential variable among them. Thus, the stress concentration factor is expressed as a function of modulus ratio in the derivation. It is found that the proposed model gives a good agreement with finite element results and has the capability to correctly predict the values of interfacial shear stresses and local stress variations in the small fiber aspect ratio regime.

• 대한기계학회논문집A
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• 제38권2호
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• pp.167-175
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• 2014

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.

• Steel and Composite Structures
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• 제18권6호
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• pp.1465-1478
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• 2015

The effect of cutting off fibers on transient load in a polymeric matrix composite lamina was studied in this paper. The behavior of fibers was considered to be linear elastic and the matrix behavior was considered to be linear viscoelastic. To model the viscoelastic behavior of matrix, a three parameter solid model was employed. To conduct this research, finite difference method was used. The governing equations were obtained using Shear-lag theory and were solved using boundary and initial conditions before and after the development of break. Using finite difference method, the governing integro-differential equations were developed and normal stress in the fibers is obtained. Particular attention is paid the dynamic overshoot resulting when the fibers are suddenly broken. Results show that considering viscoelastic properties of matrix causes a decrease in dynamic load concentration factor and an increase in static load concentration factor. Also with increases the number of broken fibers, trend of increasing load concentration factor decreases gradually. Furthermore, the overshoot of load in fibers adjacent to the break in a polymeric matrix with high transient time is lower than a matrix with lower transient time, but the load concentration factor in the matrix with high transient time is lower.

• 대한조선학회지
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• 제7권2호
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• pp.27-40
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• 1970

The distribution of stress and strain in elastic stages is investigated by the experiments of two dimensional photoelastic coating and Moire fringe method. Center block type and cover plate type of fillet welds are used as specimens in the test. The results are as follows. 1) Center block type gets less uniform stress distribution than cover plate type. And its stress concentration factor, especially at root, is larger than that at toe. 2) When main plate and cover plate closely contact and it cause friction, stress concentration decreases more than that in case of slit. That is because stress can be transmitted on the contact surface. 3) When slit is made, the outside of fillet gets more stress than the inside of it. 4) While the plastic strain distribution of center block type reaches the maximum at root and differs very slightly from that under lower loading, the plastic strain distribution of cover plate type is inclined to get the maximum at the outside of fillet rather than at root. 5) When the plastic strain value of cover plate type is compared with that of center block type at toe and root, the relations between the former and the latter shows root<toe and root>toe. 6) Because stress distribution becomes changed according to loading, fracture angle cannot be estimated by the peaks of elastic stress distribution. 7) The strain distribution just before fracture can be found by Moire fringe method.

• Journal of Biosystems Engineering
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• 제15권3호
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• pp.177-185
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• 1990

The break of rotary blade is occured from a stress concentration of the inside of blade by the outside impulsive load. In order to examine its inside stress and stress concentration of rotary blade, a epoxy plate which is suitable to applicate by photoelastic system is used to experiment. These results are summarized as follow. 1. Refer to the existence of bolt hole and a size of its of rotary blade, a stress concentration which cause the break of rotary blade is not exposed. 2. It is expected to be break to section of hold of rotary blade and the break of this is due to that there are concentrated by shearing force, bending moment and bending stress. 3. When the crack which caused from processing are set up to any location, the stress concentration taken to the creak point. 4. Without regard to the location of the reaction points of rotary blade, the bending stress which is greated than the bending moment is occured within about 6 em toward the center line of bolt hole and it was possible to break that section.