• 산업기술연구
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• 제15권
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• pp.217-222
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• 1995

In this paper, the importance of the size effects on the strength ratio is demonstrated by numerical results. The rate of decrease of tensile strength is for glass fiber, based on the experience of a composite manufacturing specialist. For other material, similar procedure may be used until detailed test result on such material is available. The strength criteria used is that of Tsai-Wu for stress space. The factors influencing the ratio are, reducing the tensile strength alone or both tensile and compression strengths, selection of the normalized interaction term, that is, the generalized Von Mises criterion or the Hill's criterion, and the status of applied stresses. Some of the numerical results are presented for a guideline for the furture study.

• 소성∙가공
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• 제25권2호
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• pp.91-95
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• 2016

This paper is concerned with modeling of a ductile fracture criterion for sheet metal considering anisotropy to predict the sudden fracture of advanced high strength steel (AHSS) sheets during complicated forming processes. The Lou−Huh ductile fracture criterion is modified using the Hill’s 48 anisotropic plastic potential instead of the von Mises isotropic plastic potential to take account of the influence of anisotropy on the equivalent plastic strain at the onset of fracture. To determine the coefficients of the model proposed, a two dimensional digital image correlation (2D-DIC) method is utilized to measure the strain histories on the surface of three different types of specimens during deformation. For the derivation of an anisotropic ductile fracture model, principal stresses (𝜎₁,𝜎₂, 𝜎₃) are expressed in terms of the stress triaxiality, the Lode parameter, and the equivalent stress (𝜂_𝐻, 𝐿,) based on the Hill’s 48 anisotropic plastic potential. The proposed anisotropic ductile fracture criterion was quantitatively evaluated according to various directions of the maximum principal stress. Fracture forming limit diagrams were also constructed to evaluate the forming limit in sheet metal forming of AHSS sheets over a wide range of loading conditions.

• 한국자동차공학회논문집
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• 제15권6호
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• pp.50-61
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• 2007

The structural stiffness, strength and stability on the bodyshell and floor structures of the Korean Low Floor Bus composed of laminate, sandwich panels and metal reinforced frame were evaluated. The laminate composite panel and facesheet of sandwich panel were made of WR580/NF4000 glass fabric/epoxy laminate, while aluminum honeycomb or balsa was applied to the core materials of the sandwich panel. A finite element analysis was used to verify the basic design requirements of the bodyshell and the floor structure. The use of aluminum reinforced frame and honeycomb core was beneficial for weight saving and structural performance. The symmetry of the outer and inner facesheet thickness of sandwich panels did not affect the structural integrity. The structural strength of the panels was evaluated using Von-Mises criterion for metal structures and total laminate approach criterion for composite structures. All stress component of the bodyshell and floor structures were safely located below the failure stresses. The total laminate approach is recommended to predict the failure of hybrid sandwich composite structures at the stage of the basic design.

• 소성∙가공
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• 제12권5호
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• pp.479-486
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• 2003

This paper presents an elastoplastic analysis for spent nuclear fuel disposal container and its 50 cm thick bentonite buffer to predict the collapse of the container while the horizontal asymmetric sudden rock movement of 10 cm is applied on the composite structure. This sudden rock movement is anticipated by the earthquake etc. at a deep underground. Elastoplastic material model is adopted. Drucker-Prager yield criterion is used for the material yield prediction of the bentonite buffer and von-Mises yield criterion is used for the material yield prediction of the container. Analysis results show that even though very large deformations occur beyond the yield point in the bentonite buffer, the container structure still endures elastic small strains and stresses below the yield strength. Hence, the asymmetric 50 cm thick bentonite buffer can protect the container safely against the 10 cm sudden rock movement by earthquake etc.. Analysis results also show that bending deformations occur in the container structure due to the shear deformation of the bentonite buffer. The finite element analysis code, NISA, is used for the analysis.

• 전산구조공학
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• 제3권3호
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• pp.113-123
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• 1990

본 연구에서는 개선된 degenerated 쉘 유한요소의 탄소성 및 기하학적 비선형 해석에의 적용성을 고찰하였다. 본 연구의 개선된 degenerated 쉘요소는 shear locking 해결에 우수한 결과를 보인 가정된 전단변형도를 대치사용하고, membrance locking 현상을 제거하기위해 평면내 변형도의 구성시 감차적분을 행하며, 쉘요소 자체의 거동을 보완하기위해 비적합변위형을 선택적으로 추가하였다. 본 요소는 shear/membrance locking이 발생하지 않으며, 전달가능한 거짓 영에너지모드도 나타나지않는다. 소성변형 정형화에서는 적층모델을 사용하며, 재료는 von Mises항복조건을 따른다고 가정한다. 유한변형을 고려한 기하학적 비선형 방정식을 total lagrangian수식화를 사용하여 정형화 하였고, 비선형 방정식은 하중제어 및 변위제어법을 사용한 Newton-Raphson 반복법으로 반복 계산한다. 여러 예제해석을 통하여 본 개선된 degenerated 쉘 유한요소의 정확도를 고찰하였다.

• Smart Structures and Systems
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• 제21권5호
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• pp.591-600
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• 2018

The probabilistic characterization of wind field characteristics is a significant task for fatigue reliability assessment of long-span railway bridges in wind-prone regions. In consideration of the effect of wind direction, the stochastic properties of wind field should be represented by a bivariate statistical model of wind speed and direction. This paper presents the construction of the bivariate model of wind speed and direction at the site of a railway arch bridge by use of the long-term structural health monitoring (SHM) data. The wind characteristics are derived by analyzing the real-time wind monitoring data, such as the mean wind speed and direction, turbulence intensity, turbulence integral scale, and power spectral density. A sequential quadratic programming (SQP) algorithm-based finite mixture modeling method is proposed to formulate the joint distribution model of wind speed and direction. For the probability density function (PDF) of wind speed, a double-parameter Weibull distribution function is utilized, and a von Mises distribution function is applied to represent the PDF of wind direction. The SQP algorithm with multi-start points is used to estimate the parameters in the bivariate model, namely Weibull-von Mises mixture model. One-year wind monitoring data are selected to validate the effectiveness of the proposed modeling method. The optimal model is jointly evaluated by the Bayesian information criterion (BIC) and coefficient of determination, $R^2$. The obtained results indicate that the proposed SQP algorithm-based finite mixture modeling method can effectively establish the bivariate model of wind speed and direction. The established bivariate model of wind speed and direction will facilitate the wind-induced fatigue reliability assessment of long-span bridges.

• 한국강구조학회 논문집
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• 제12권4호통권47호
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• pp.351-362
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• 2000

이 논문은 반복하중을 받는 관통형 고력볼트를 사용한 엔드플레이트형식 콘크리트 충전 각형강관 기둥-H형강 보 접합부의 거동에 관한 연구이다. 주요변수는 엔드플레이트의 두께(16mm, 22mm, 25mm)와 기둥의 두께(9mm, 12mm)이다. 각 변수에 대해 실험결과와 비교 분석한다. 보-기둥 접합부의 에너지 흡수능력을 구하고, 접합부 패널의 전단내력을 분석한다. 접합부 패널의 전단 내력은 von Mises 항복조건에 의한 강재의 내력과 콘크리트 충전효과를 고려한 Strut 모델을 사용한 콘크리트의 내력을 단순누가해서 구한다.

• 콘크리트학회지
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• 제9권2호
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• pp.133-144
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• 1997

2차원 응력상태의 철근콘크리트 부재해석을 위하여 소성이론과 파괴모델의 통합방법을 연구하였다. 콘크리트의 대별되는 두 가지 거동특성인 다차원 압축상태의 강도증가와 인장균열파괴를 동시에 나타내기 위하여, 압축파괴와 인장균열의 다중파괴기준을 사용하는 소성이론을 근간으로 여러 실험결과를 반영하는 파괴모델을 적용한다. 압축파괴기준으로서 Drucker-Prager모델과 von Mises 모델을 비교 사용하며 인장균열거동에 대하여 회전균열소성모델과 고정균열소성모델을 비교한다. 이러한 압축파괴기준과 이장균열파괴기준의 설정에는 다차원 압축상태의 강도증가, 균열로 인한 인장과 압축응력도의 저하, 보강철근의 영향등을 나타내는 실험식과 파괴에너지개념을 사용한다. 이 재료모델을 비선형유한요소해석에 사용하여 기존의 실험결과와 비교한다. 재료모델의 압축파괴와 인장균열거동을 검증하기 우하여 콘크리트의 압축파괴 또는 철근의 인장항복에 의하여 거동이 대별되는 실험들과 비교한다.

• 전산구조공학
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• 제10권2호
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• pp.189-201
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• 1997

국내 보도육교의 경우, 단순한 구조형식과 공장제작에 의한 현장조립의 신속한 시공 및 유지관리상의 장점들로 인하여 표준화된 강상형 보고육교가 교통혼잡이 심한 도심지와 각종 국도상에 다수 건설되어 왔지만, 이중 상당수의 육교가 공용년수 증가와 더불어 열화손상되어 안전도 및 사용성이 매우 불량한 상태에 있다. 본 논문에서는 열화손상된 기존의 강상형 보도육교의 실제적인 안전도 및 잔존내하력을 평가하기 위하여 선진각국에서는 이미 일반화되고 있는 von Mises'조합응력항복기준에 기반을 둔 한계상태설계법에 기초하여 각 구조부위의 항복 및 좌굴에 대한 각각의 비선형 한계상태모형을 제안하고 이를 실구조물에 적용해서 안전도평가 및 신뢰성평가를 수행하여 제안된 모형의 타당성을 고찰하였다. 뿐만아니라 노후된 기존 강상형 보도육교에 대한 현장재하시험 방법과 이들 시험결과를 이용한 실용적이고 합리적인 잔존내하력 평가방법을 제안하고 각국 시방서별/설계방법별로 비교, 고찰하였다.

• Smart Structures and Systems
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• 제23권4호
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• pp.329-335
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• 2019

Structural fuses are made up from oriented steel plates to be used to resist seismic force with shear loading resistance capabilities. The damage and excessive inelastic deformations are concentrated in structural fuses to avoid any issues for the rest of the surrounding elements. Recently developed fuse plates are designed with engineered cutouts leaving flexural or shear links with controlled yielding features. A promising type of link is proposed to align better bending strength along the length of the link with the demand moment diagram is a butterfly-shaped link. Previously, the design methodologies are purely based on the flexural stresses, or shear stresses only, which overestimate the dampers capability for resisting against the applied loadings. This study is specifically focused on the optimized design methodologies for commonly used butterfly-shaped dampers. Numerous studies have shown that the stresses are not uniformly distributed along the length of the dampers; hence, the design methodology and the effective implementation of the steel need revisions and improvements. In this study, the effect of shear and flexural stresses on the behavior of butterfly-shaped links are computationally investigated. The mathematical models based on von-Mises yielding criteria are initially developed and the optimized design methodology is proposed based on the yielding criterion. The optimized design is refined and investigated with the aid of computational investigations in the next step. The proposed design methodology meets the needs of optimized design concepts for butterfly-shaped dampers considering the uniform stress distribution and efficient use of steel.