• 전산구조공학
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• 제9권3호
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• pp.179-186
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• 1996

본 연구에서는 구조체의 위상학적 최적화를 위한 비선형 formulation(NLP)가 개발, 검토되었다. 이 NLP는 multiple-loading하에서 임의의 오브젝티브 함수, 응력, 변위 제약조건들을 쉽게 다룰 수가 있다. 또한 이 NLP는 해석과 최적화 디자인을 동시에 실시함으로써 요소 사이즈가 영으로 접근함에 따른 강성 매트릭스의 singularity를 피할 수 있다. 즉, 평형 방정식을 등제약조건으로 치환함으로써 강성 매트릭스 그 자체나 그의 역매트릭스를 구할 필요도 없어진다. 이 NLP는 multiple-loading conditon하에서 테스트되었으며, 이를 통해 이 NLP가 다양한 제약조건하에서 강력하게 작용함이 입증되었다.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1290-1300
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• 1996

The finite element method, based on rigid-plastic formulation, is widely used to simulate metal forming processes. In order to improve the computational efficiency of the rigid-plastic FEM, one-point integration is used to evaluate the stiffness matrix with four-node rectangular elements and eight-node brick elements. In order to control the hourglass modes, hourglass strain rate components were introduced and included in the effective strain rate definition, Numerical tests have shown that the proposed one-point integration scheme reduces the stiffness matrix evaluation time without deteriorating the convergence behavior of Newton-Raphson method. Simulations of a ring compression, a plane-strain closed-die forging and the three-dimensional spike forging processes were carried out by using the proposed integration method. The simulation results are compared to those obtained by applying the conventional integraiton method in terms of the solution accuracy and computational efficiency.

• Structural Engineering and Mechanics
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• 제53권2호
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• pp.205-226
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• 2015

Finite element method (FEM) is an effective quantitative method to solve complex engineering problems. The basic idea of FEM for a complex problem is to be able to find a solution by reducing the problem made simple. If mathematical tools are inadequate to obtain precise result, even approximate result, FEM is the only method that can be used for structural analyses. In FEM, the domain is divided into a large number of simple, small and interconnected sub-regions called finite elements. FEM has been used commonly for linear and nonlinear analyses of different types of structures to give us accurate results of plane stress and plane strain problems in civil engineering area. In this paper, FEM is used to investigate stress analysis of a shear wall which is subjected to concentrated loads and fundamental principles of stress analysis of the shear wall are presented by using matrix displacement method in this paper. This study is consisting of two parts. In the first part, the shear wall is discretized with constant strain triangular finite elements and stiffness matrix and load vector which is attained from external effects are calculated for each of finite elements using matrix displacement method. As to second part of the study, finite element analysis of the shear wall is made by ANSYS software program. Results obtained in the second part are presented with tables and graphics, also results of each part is compared with each other, so the performance of the matrix displacement method is demonstrated. The solutions obtained by using the proposed method show excellent agreements with the results of ANSYS. The results show that this method is effective and preferable for the stress analysis of shell structures. Further studies should be carried out to be able to prove the efficiency of the matrix displacement method on the solution of plane stress problems using different types of structures.

• Interaction and multiscale mechanics
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• 제2권3호
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• pp.321-332
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• 2009

Recent development in composites containing phase-transforming particles, such as vanadium dioxide or barium titanate, reveals the overall stiffness and viscoelastic damping of the composites may be unbounded (Lakes et al. 2001, Jaglinski et al. 2007). Negative stiffness is induced from phase transformation predicted by the Landau phase transformation theory. Although this unbounded phenomenon is theoretically supported with the composite homogenization theory, detailed stress analyses of the composites are still lacking. In this work, we analyze the stress distribution of the Hashin-Shtrikman (HS) composite and its two-dimensional variant, namely a circular inclusion in a square plate, under the assumption that the Young's modulus of the inclusion is negative. Assumption of negative stiffness is a priori in the present analysis. For stress analysis, a closed form solution for the HS model and finite element solutions for the 2D composite are presented. A static loading condition is adopted to estimate the effective modulus of the composites by the ratio of stress to average strain on the loading edges. It is found that the interfacial stresses between the circular inclusion and matrix increase dramatically when the negative stiffness is so tuned that overall stiffness is unbounded. Furthermore, it is found that stress distributions in the inclusion are not uniform, contrary to Eshelby's theorem, which states, for two-phase, infinite composites, the inclusion's stress distribution is uniform when the shape of the inclusion has higher symmetry than an ellipse. The stability of the composites is discussed from the viewpoint of deterioration of perfect interface conditions due to excessive interfacial stresses.

• 대한토목학회논문집
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• 제29권1A호
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• pp.31-43
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• 2009

본 논문에서는 다양한 차종의 영향을 반영할 수 있고, 차량과 교량의 연성 운동방정식을 구성하여 시간 단계별 직접해를 산정할 수 있는 수치해석기법을 제시하였다. 운동방정식의 해는 직접적분법인 Newmark ${\beta}$을 이용하여 해석 단계별로 구성된 유효강성행렬과 유효하중벡터를 바탕으로 정적평형방정식의 해를 구하는 원리와 동일하게 산정하였다. 또한 해석의 효율성을 증진시키기 위하여 유효강성행렬은 Skyline 법에 의해 재구성하였으며, Cholesky의 행렬 분해기법을 동시에 적용하여 직접적인 역행렬 계산에서 야기되는 오차의 발생을 최소화 하였다. 또한 기존선 철도차량인 새마을 PMC 열차와 디젤 견인 무궁화 열차에 대한 3차원 정밀수치해석 모델을 개발하였고, 각 차량은 차체와 전 후방 대차에 각각 6자유도씩 고려하여 총 18자유도로 수치모델을 작성하였다. 교량은 3차원 공간뼈대 요소를 이용하여 모델링하였고, 차륜과 레일 접촉면의 불규칙성은 미국의 FRA에서 규정하고 있는 연직방향 및 횡방향틀림에 대한 PSD 함수를 이용하여 궤도틀림을 수치적으로 구현하였다. 제시된 수치해석 기법은 12 m, 18 m형 판형교의 실측결과를 이용하여 타당성을 검증하였으며, 실측 및 수치해석결과는 교량의 1차 휨 고유진동수의 2.0배를 기준으로 Low pass filtering 하였다.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1320-1332
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• 1996

In the present study, we consider modified 5-node equivalent solid element which has smallest degree of freedom among 2-dimensional solid elements accounting bending deformation as well as extensional and shear deformations, We shall investigate static and dynamic characteristics of this element, which is very effective in thin beam, thick beam, large displacement problems, beam of variable thickness, and asymmetrically stepped beam, etc., as well as relatively simple problems of beam. The degree of freedom of this element is 10, which is smaller than 18 of 9-node element, 16 of 8-node elemtns, 12 of modified 6-node element and Q6 element. Therefore, this element is expected to broaden the effective range of application of the solid elements in the bending problems further.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.319-324
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• 1999

This study is to investigate the properties on the load-deflection and fracture behaviors of the steel fiber reinforced concrete(SFRC) slab model specimens, Steel fibers of indent, crimp, and end hook shape were considered to reinforce the matrix under various mixing conditions and proportions. Initial cracking load, maximum load, and energy absorption capacity(load carrying capacity) of SFRC panel specimen increased with increase of steel fiber contents. And the plain concrete slab was fractured abruptly after maximum load but SRFC slabs were fractured smoothly by steel fibers in concrete matrix operated as cracking resistance force after maximum load. Indent, crimp and end hook shape steel fibers were effective in reinforcing the matrices but end hook type fiber were superior to indent and crimp type fibers.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2013년도 춘계학술대회 논문집
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• pp.38-38
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• 2013

The mechanical cues that adherent cells derive from the extracellular matrix (ECM) can effect dramatic changes in cell migration, proliferation, and differentiation. Using a thin film of Type I collagen fibrils comprised of 100 nm to 200 nm collagen fibrils overlaying a bed of smaller fibrils, changes in cellular response to systematically controlled changes in mechanical properties of collagen was investigated. Further, an experimental and modeling approaches to calculate the elastic modulus of individual collagen fibrils, and thereby the effective stiffness of the entire collagen thin film matrix, from atomic force microscopy force spectroscopy data was performed. These results demonstrate an approach to analysis of fundamental properties of thin, heterogeneous, organic films, and add further insights into the mechanical properties of collagen fibrils that are of relevance to cell response to the ECM.

• 대한기계학회논문집
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• 제13권3호
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• pp.317-322
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• 1989

본 연구에서는 Liu의 매트릭스를 강소성 유한요소법에 도입하여 통상의 소성가공 공정중에 있는 피가공물의 3차원 변형을 실용적인 수준에서 해석 가능케 하는 강소성 유한요소법을 도입하여 통상의 소성가공 공정중에 있는 피가공물의 3차원 변형을 실용적인 수준에서 해석 가능케 하는 강소성 유한요소법을 제안하고 실례를 통하여 제안한수법에 의하여 얻어진 해의 안정성과 계산효율을 검토한다.

• Composites Research
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• 제30권4호
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• pp.247-253
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• 2017

본 연구에서는 분자동역학 전산모사와 이중 입자 모델을 이용하여 질화붕소 나노튜브-폴리메틸메타크릴레이트 나노복합재의 기계적 물성과 계면특성을 규명하였다. 단일 벽 나노튜브가 고분자 기지에 함침된 가로등방성 나노복합재 단위 셀 구조를 모델링한 후, 각 방향으로의 일축인장 및 전단 전산모사를 통해 나노복합재의 강성행렬을 예측하였다. 또한 강성행렬의 방향 평균을 취해 나노튜브가 기지 내에 랜덤 분포하는 경우의 등방성 탄성계수를 도출하였다. 분자동역학 해석 결과를 계면의 완전 결합을 가정한 이중 입자 모델 예측해와 비교한 결과, 질화붕소 나노튜브와 고분자 기지간의 계면이 불완전한 것으로 확인되었다. 나노튜브 주위에 형성되는 흡착계면의 물성을 예측하기 위해 2단계 영역 분할 기법을 도입하였고 계면의 불완전 결합을 선형 스프링으로 묘사하였다. 그 결과 다양한 스프링 컴플라이언스 값에 따른 흡착계면의 물성을 역 해석을 통해 확인할 수 있었다.