• 한국산학기술학회논문지
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• 제13권8호
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• pp.3295-3300
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• 2012

3차원 유한요소법은 구조물에 존재하는 표면균열과 내재균열들의 응력확대계수를 구하는데 이용되어 진다. 기하모델, 즉 솔리드모델은 3차원 균열들을 포함하고 있다. 국부적인 절점밀도가 선택되어 지면 자동적으로 기하모델 영역에 중첩되어 지며 절점은 버블패깅 방법에 의해 생성되어지고 10절점 사변형 솔리드요소는 데라우니 삼각화 기술에 의해 생성하였다. 시스템의 정확도와 효용성을 체크하기 위해 인장하중을 받는 평판에 하나의 균열이 존재하는 경우의 응력확대계수를 구해 Raju-Newnam식과 비교하여 5%이내의 차이를 보였다. 또한, 인장하중을 받는 평판에 두개 균열이 존재하는 경우의 해석을 통해 상호 간섭 효과를 분석하였다.

• Structural Engineering and Mechanics
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• 제86권1호
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• pp.69-83
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• 2023

Analytical solutions to problems are crucial because they provide high-quality comparison data for assessing the accuracy of numerical solutions. Benchmark analytical solutions for the vibrations of cracked functionally graded material (FGM) plates are not available in the literature because of the high level of complexity of such solutions. On the basis of first-order shear deformation plate theory (FSDT), this study proposes analytical series solutions for the vibrations of FGM rectangular plates with side or internal cracks parallel to an edge of the plates by using Fourier cosine series and the domain decomposition technique. The distributions of FGM properties along the thickness direction are assumed to follow a simple power law. The proposed analytical series solutions are validated by performing comprehensive convergence studies on the vibration frequencies of cracked square plates with various crack lengths and under various boundary condition combinations and by performing comparisons with published results based on various plate theories and the theory of three-dimensional elasticity. The results reveal that the proposed solutions are in excellent agreement with literature results obtained using the Ritz method on the basis of FSDT. The paper also presents tabulations of the first six nondimensional frequencies of cracked rectangular Al/Al2O3 FGM plates with various aspect ratios, thickness-to-width ratios, crack lengths, and FGM power law indices under six boundary condition combinations, the tabulated frequencies can serve as benchmark data for assessing the accuracy of numerical approaches based on FSDT.

• 대한기계학회논문집A
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• 제38권12호
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• pp.1441-1446
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• 2014

본 논문에서는 휜 광폭평판의 두께와 폭, 균열길이 그리고 가공경화지수의 변화가 휜 광폭평판의 균열부 구속상태에 미치는 영향을 평가하였다. 이를 위해 5가지의 휜 광폭평판 두께, 3가지의 균열길이, 3가지의 휜 광폭평판 폭 그리고 3가지의 가공경화지수를 고려한 3차원 탄소성 유한요소해석을 수행하였다. Ramberg-Osgood 관계식을 만족하는 비선형 재료로 가정하였으며 균열부 구속상태를 정량화하기 위해서 Q-응력을 이용하였다. 3차원 유한요소해석 결과를 바탕으로 기하학적 형상 및 재료특성에 따른 휜 광폭평판의 Q-응력 변화를 평가하였다. 평가 결과 면외 구속조건에 의한 영향은 면내 구속조건과 밀접한 관계가 있었으며, 면외 구속조건이 면내 구속조건 보다 균열부 구속상태에 더 큰 영향을 미쳤다.

• Composites Research
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• 제14권1호
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• pp.8-14
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• 2001

복합재 적층판의 자유단 층간분리의 모드별 변형률 에너지 해방률을 구하는 간이 계산법을 제안하였다. 층간응력은 층간에서의 평형식으로부터 층간의멘트와 층간전단력으로 평가하였다. 적층판 자유단 층간분리의 변형은 일반화된 준3차원 고전적층이론에 의하여 계산하였다. 이 간이 계산법은 변형균 에너지 해방률의 세성분을 구하는 간편한 식으로 나타내었다 복합재 적층판이 일축인장을 받는 경우에 대하여 적층판 중앙면에 대칭과 비대칭인 층간분리가 발생한 경우에 대하여 해석을 행하였다. 해석결과는 가상분리진전법에 의한 유한요소해석결과와 잘 일치하였다.

• 대한기계학회논문집A
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• 제37권4호
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• pp.521-527
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• 2013

본 논문에서는 3 차원 유한요소해석을 통해 표면균열이 있는 직관에 내압, 굽힘, 그리고 비틀림의 단일 또는 복합하중이 작용하는 경우의 응력확대계수를 연구하였다. 두 가지 결함평가코드(API-579-1, RCC-MR A16)를 각각 유한요소해석 결과와 비교하여 코드 간의 차이 및 해석의 신뢰성을 확인하였다. 응력확대계수는 적분 경로에 독립적이기 때문에 민감하지 않다고 알려져 있는데 3 차원 유한요소해석을 통해 요소 수에 대한 민감도를 확인하였다. 또한 균열형상의 정의방법에 따른 유한요소해석 결과의 차이와 두 가지 결함평가코드를 사용한 결과의 차이를 확인하였다.

• 한국생산제조학회지
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• 제22권3_1spc호
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• pp.573-579
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• 2013

Once-through helically coiled steam generator tubes subjected to external pressure are of interest because of their application to advanced small- and medium-sized integral reactors, in which a primary coolant with a relatively higher pressure flows outside the tubes, while secondary water with a relatively lower pressure flows inside the tubes. Another notable point is that the values of the mean radius to thickness ratio of these steam generator tubes are very small, which means that a thick-walled cylinder is employed for these steam generator tubes. In the present paper, the maximum allowable pressure of helically coiled and thick-walled steam generator tubes with through-wall cracks under external pressure is investigated based on a detailed nonlinear three-dimensional finite element analysis. In terms of the crack orientation, either circumferential or axial through-wall cracks are considered. In particular, in order to quantify the effect of the crack location on the maximum external pressure, these cracks are assumed to be located in the intrados, extrados, and flank of helically coiled cylinders. Moreover, an evaluation is also made of how the maximum external pressure is affected by the ovality, which might be inherently induced during the tube coiling process used to fabricate the helically coiled steam generator tubes.

• Smart Structures and Systems
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• 제18권3호
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• pp.405-423
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• 2016

In this study, the feasibility of using telecommunication single-mode optical fiber (SMF) as a distributed fiber optic strain and crack sensor was evaluated in concrete pavement monitoring. Tensile tests on various sensors indicated that the $SMF-28e^+$ fiber revealed linear elastic behavior to rupture at approximately 26 N load and 2.6% strain. Six full-scale concrete panels were prepared and tested under truck and three-point loads to quantify the performance of sensors with pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA). The sensors were protected by precast mortar from brutal action during concrete casting. Once air-cured for 2 hours after initial setting, half a mortar cylinder of 12 mm in diameter ensured that the protected sensors remained functional during and after concrete casting. The strains measured from PPP-BOTDA with a sensitivity coefficient of $5.43{\times}10^{-5}GHz/{\mu}{\varepsilon}$ were validated locally by commercial fiber Bragg grating (FBG) sensors. Unlike the point FBG sensors, the distributed PPP-BOTDA sensors can be utilized to effectively locate multiple cracks. Depending on their layout, the distributed sensors can provide one- or two-dimensional strain fields in pavement panels. The width of both micro and major cracks can be linearly related to the peak strain directly measured with the distributed fiber optic sensor.

• 대한기계학회논문집
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• 제19권5호
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• pp.1259-1268
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• 1995

The stress distribution around micro holes and the behavior of stress interaction between micro holes are considerd in the study. Several conclusions are extracted as follows : (1) The stress interaction varies with the distance e between micro holes. When the two micro holes are spaced in such a manner that theri two closest points are separated by a distance of micro hole radius (e=1), stress distribution is affected by a opposite micro hole in all the closest region. In addition, if two closest points are seperated by twice the distance of a micro hole radius (e=2), stress distribution is affected by a opposite micro hole in the region of -0.8.leq.x/r.leq.0.8 and the interaction effect can be neglected for e=4. (2)If the depth becomes larger than the radius, or the radius varies, the shape and magnitude of stress distribution around micro holes varies. (3) Hoop stress around a micro hole for the two dimensional configuration is larger than that of the three dimensional micro hole located on the surface of material for .theta. < 60.deg., but it is reversed for .theta > 60.deg.

• Structural Engineering and Mechanics
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• 제68권5호
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• pp.537-547
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• 2018

This research presents the effect of anisotropy of the hollow disc mode under Brazilian test using PFC3D. The Brazilian tensile strength test was performed on the hollow disc specimens containing the bedding layers and then these specimens were numerically modeled by using the two dimensional discrete element code (PFC3D) to calibrate this computer code for the simulation of the cracks propagation and cracks coalescence in the anisotropic bedded rocks. The thickness of each layer within the specimens varied as 5 mm, 10 mm and 20 mm and the layers angles were changed as $0^{\circ}$, $25^{\circ}$, $50^{\circ}$, $75^{\circ}$ and $90^{\circ}$. The diameter of internal hole was taken as 15 mm and the loading rate during the testing process kept as 0.016 mm/s. It has been shown that for layers angles below $25^{\circ}$ the tensile cracks produce in between the layers and extend toward the model boundary till interact and break the specimen. The failure process of the specimen may enhance as the layer angle increases so that the Brazilian tensile strength reaches to its minimum value when the bedding layers is between $50^{\circ}$ and $75^{\circ}$ but its value reaches to maximum at a layer angle of $90^{\circ}$. The number of tensile cracks decreases as the layers thickness increases and with increasing the layers angle, less layer mobilize in the failure process.

• 한국소음진동공학회논문집
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• 제13권5호
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• pp.400-408
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• 2003

This paper investigates the vibration characteristics of steam generator (SG) U-tubes with defect. The operating SG shell-side flow field conditions for determining the fluidelastic instability parameters such as added mass are obtained from three-dimensional SG flow calculation. Modal analyses are performed for the U-tubes either with axial or circumferential flaw with different sizes. Special emphases are on the effects of flaw orientation and size on the modal and instability characteristics of tubes, which are expressed in terms of the natural frequency, corresponding mode shape and stability ratio. Also, addressed is the effect of the internal pressure on the vibration characteristics of the tube.