• Structural Engineering and Mechanics
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• 제2권4호
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• pp.359-367
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• 1994

The stability behaviour of symmetrically laminated rectangular composite plates with loaded ends clamped and unloaded edges simply-supported, and subjected to uniform in-plane compression is investigated. A numerical and experimental investigation is presented in this contribution. The stacking sequence of the laminated glass/epoxy composite plates is symmetric about the middle surface and consists of 8-ply [0, 90, +45, -45]s lamination. Numerical predictions were obtained through the use of the finite element method. The above plates were modelled with 8-noded isoparametric layered shell elements. The effect of the input parameters such as the degree and forms of prescribed initial imperfection and the incremental step size required for incremental loading, on the convergence of the solution is thoroughly examined. Experimental results are presented for 10 test panels. All test panels were made from glass/epoxy unidirectional prepregs and have aspect ratio of 5.088. The laminate thicknesses were found to vary from 1.054 mm to 1.066 mm. Comparison of experimental data with predicted results show good correlation and give confidence in the finite element model.

• Composites Research
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• 제30권2호
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• pp.149-157
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• 2017

본 논문에서는 응집영역 모델링 기법을 사용하여 노치가 있는 적층복합재료의 파괴거동을 연구하였다. 먼저 노치가 있는 적층복합재료 시편형상에 대해 일반 3차원 고체요소로 모델링 한 후 요소들 사이에 섬유파괴, 기지파괴 및 층간분리 파괴를 담당하는 응집요소를 삽입하여 유한요소 메쉬를 제작하였다. 다음으로 일축인장 시험을 모사하는 하중 및 경계조건을 가하여 점진적 파괴해석을 수행하고 해석결과를 참고문헌의 실험결과와 비교하여 해석의 타당성을 검증하였다. 수치해석 결과로부터 노치가 있는 적층복합재료 인장시편의 파괴시작 및 진전거동을 분석하였으며 파괴모드의 진전을 체계적으로 조사하였다.

• Smart Structures and Systems
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• 제16권6호
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• pp.1023-1047
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• 2015

In this study, the optimal location of the MR fluid segments in a partially treated laminated composite sandwich plate has been identified to maximize the natural frequencies and the loss factors. The finite element formulation is used to derive the governing differential equations of motion for a partially treated laminated composite sandwich plate embedded with MR fluid and rubber material as the core layer and laminated composite plate as the face layers. An optimization problem is formulated and solved by combining finite element analysis (FEA) and genetic algorithm (GA) to obtain the optimal locations to yield maximum natural frequency and loss factor corresponding to first five modes of flexural vibration of the sandwich plate with various combinations of weighting factors under various boundary conditions. The proposed methodology is validated by comparing the natural frequencies evaluated at optimal locations of MR fluid pockets identified through GA coupled with FEA and the experimental measurements. The converged results suggest that the optimal location of MR fluid pockets is strongly influenced not only by the boundary conditions and modes of vibrations but also by the objectives of maximization of natural frequency and loss factors either individually or combined. The optimal layout could be useful to apply the MR fluid pockets at critical components of large structure to realize more efficient and compact vibration control mechanism with variable damping.

• 한국공작기계학회논문집
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• 제13권4호
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• pp.16-22
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• 2004

Shape optimization was performed to obtain the precise shape of cutouts including the internal shape of cutouts in laminated composite plates by three dimensional modeling using solid element. The volume control of the growth-strain method was implemented and the distributed parameter chosen as Tsai-Hill fracture index for shape optimization. The volume control of the growth-strain method makes Tsai-Hill failure index at each element uniform in laminated composites under the initial volume. Then shapes optimized by Tsai-Hill failure index were compared with those of the initial shapes for the various load conditions and cutouts. The following conclusions were obtained in this study (1) It was found that growth-strain method was applied efficiently to shape optimization of three dimensional cutouts in a laminated composite plate, (2) The optimal shapes on the various load conditions and cutouts were obtained, (3) The maximum Tsai-Hill failure index was reduced up to 67% when shape optimization was performed under the initial volume by volume control of growth-strain method.

• 한국추진공학회지
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• 제10권4호
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• pp.47-53
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• 2006

본 논문에서는 탄소-페놀 복합재로 제조된 로켓 노즐 내열부품의 고온에서의 거동을 3차원 축대칭 유한요소 모델을 사용하여 해석하였다. 실제 작동 조건을 사용하여 카울 영역의 적층링을 해석한 결과 층각도, 축방향 치수, 경계조건은 적층링 내부의 응력 분포에 큰 영향을 주는 것으로 확인되었다. 특히 링과 링 사이의 접합부분에서 모서리 탈락 현상의 전조 현상인 층간분리가 발생한다. 분리현상 이후에는 층각도 방향 전단응력과 축방향 압축응력에 의해 탈락 현상이 발생하는 것으로 판단된다.

• Structural Engineering and Mechanics
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• 제18권1호
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• pp.41-58
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• 2004

The postbuckling behaviour of thin shells has fascinated researchers because the theoretical prediction and their experimental verification are often different. In reality, shell panels possess small imperfections and these can cause large reduction in static buckling strength. This is more relevant in thin laminated composite shells. To study the postbuckling behaviour of thin, imperfect laminated composite shells using finite elements, explicit incremental or secant matrices have been presented in this paper. These incremental matrices which are derived using Marguerre's shallow shell theory can be used in combination with any thin plate/shell finite element (Classical Laminated Plate Theory - CLPT) and can be easily extended to the First Order Shear deformation Theory (FOST). The advantage of the present formulation is that it involves no numerical approximation in forming total potential energy of the shell during large deformations as opposed to earlier approximate formulations published in the literature. The initial imperfection in shells could be modeled by simply adjusting the ordinate of the shell forms. The present formulation is very easy to implement in any existing finite element codes. The secant matrices presented in this paper are shown to be very accurate in tracing the postbuckling behaviour of thin isotropic and laminated composite shells with general initial imperfections.

• 한국강구조학회 논문집
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• 제13권5호
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• pp.443-455
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• 2001

전단 층을 갖는 2개 매개변수 탄성지반 위에 놓인 복합재료 적층판에서 휨 진동 및 좌굴해석을 위해 에너지 방법을 사용해 탄성해를 구하였다. 복합재료 적층판의 점탄성 해석은 유사-탄성방법을 사용해 탄성해를 구하였다. 전단에 의한 효과는 3창 전단변형이론을 적용하여 고려하였다. 유도된 식들을 검증하기 위해 LUSAS 프로그램에 의한 탄성지반위에 놓인 이방성 판의 처짐과 비교하였다. 점탄성 휨 진동 및 좌굴해석에 관한 수치해석결과들은 적층순서, 적층 수 재료 비등방성과 전단지반계수 등에 따른 효과를 보여 준다.

• 한국공간구조학회:학술대회논문집
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• 한국공간구조학회 2008년도 춘계 학술발표회 논문집
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• pp.74-79
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• 2008

본 논문에서는 유한요소법을 이용하여 저속충격을 받는 복합적층판(Graphite/Epoxy)의 충격과도응답을 조사한다. 판의 대처짐을 고려한 von-Karman 이론에 Mindlin의 전단변형 효과와 회전관성 효과를 포함한 비선형 이론을 도입한다. 과도응답의 수렴은 정적만입실험을 통해 얻은 접촉법칙을 사용하며, 다양한 복합적층판의 두께 변화에 따른 접촉력, 변위응답, 변형률 등을 조사하여 비교 분석한다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.60-63
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• 2002

Metal/intermetallic laminated composites have been manufactured by SHS reactions between Ni and Al elemental metal foils. Microstructure showed that the intermetallic volume fraction was 55%, 45%, 35% in the 1:1, 2:1, 4:1 thickness ratio(Ni:Al) specimen and the main phases of the intermetallic were transformed from $Ni_2Al_3$ to NiAl when the thickness ratio was increased. Tensile strength and elongation were increased when the volume fraction of Ni metallic phase was increased. Under assumptions of isostrain condition, the tensile strength of metal/intermetallic laminated composites didn't obey the ROM due to the thermal residual stress and this was confirmed by X-ray residual stress analysis. Fracture toughness results by the SENB test showed R-curves with upward curvature based on LSB condition. Bridging stress based on LSB condition was determined by the curve fitting analysis, In-situ observed microstructure during fracture test showed that the various bridging mechanism such as crack bridging, crack branching and ductile failure of metallic layer were occurred

• 대한기계학회논문집
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• 제18권4호
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• pp.958-966
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• 1994

The postbuckling compressive strengths of $[0/90/\pm\theta]_s$ composite laminated cylindrical panels with various fiber angles and width-to-length ratios are characterized by the nonlinear finite element method. For the iteration and load-increment along the postbuckling equilibrium path a modified arc-length method in which the effect of failure can be considered is introduced. In the progressive failure analysis the maximum stress criterion and complete unloading model are used. Present finite element results show good agreement with experiments for $[0_3/90]_s$ cylindrical panel and $[0/\pm45/90/]_s$ plate. The postbuckling compressive strength of $[0/90/\pm\theta]_s$ composite laminated cylindrical panel is independent of the initial buckling stress but high in the panel with large value of the bending stiffness in axial direction. In the several cylindrical panels, it is observed that the prebuckling compressive failures occur and result into the collapse before the buckling.