• 마이크로전자및패키징학회지
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• 제20권2호
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• pp.33-38
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• 2013

In this study, both a finite element analysis and an experimental analysis are executed to investigate the mechanical characteristics of dielectric material effects on warpage. Also, viscoelastic material properties are measured by DMA and are considered in warpage simulation. A finite element analysis is done by using both thermal elastic analysis and a thermo-viscoelastic analysis to predict the nonlinear effects. For experimental study, specimens warpage of non-symmetric structure with body size of $22.5{\times}22.5$ mm, $37.5{\times}37.5$ mm and $42.5{\times}42.5$ mm are measured under the reflow temperature condition. From the analysis results, experimental warpage is not similar to FEA results using thermal elastic analysis but similar to FEA results using thermo-viscoelastic analysis. Also, its effect on substrate warpage is increased as core thickness is decreased and body size is getting larger. These FEA and the experimental results show that the nonlinear characteristics of dielectric material play an important role on substrate warpage. Therefore, it is strongly recommended that non-linear behavior characteristics of a dielectric material should be considered to control warpage of FCBGA substrate under conditions of geometry, structure and manufacturing process and so on.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 춘계학술발표대회 논문집
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• pp.43-47
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• 1999

A FEA model is proposed to study the effects of fiber waviness on tensile/comprssive nonlinear behaviors of thick unidirectional composites. In the analyses both material and geometical nonlinarities are considered. The predicted results from the FEA model are compared with those obtained from the previous analytical model (thin carpet model) Tensile/compressive tests are also conducted on the specimens with various controlled fiber waviness to obtain the nonlinear behaviors of composites experimentally. The predictions from the FEA model show better agreements with the experiments than those from the analytical model.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1993년도 가을 학술발표회논문집
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• pp.47-54
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• 1993

This paper is concerned with the geometrically nonlinear behavior of elastic systems under conservative loading conditions. In particular, the topic are snap through problems and the arc-length method to pass limit points of space trusses is used. And numerical examples are presented to trace nonlinear equilibrium paths.

• 한국자동차공학회논문집
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• 제1권2호
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• pp.42-48
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• 1993

In this paper, dynamic collapse behavior of the rectangular tube under impact loading is anlayzed using nonlinear finite element method of shell element. In case of shell element formulation using corotational element coordinates system, dynamic collapse behavior is analyzed without initial imperfection, and with initial imperfection. This paper reveals that the collapse of a rectangular tue without initial imperfection is caused by an error of transformation of the corotational coordinates system.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 추계 학술발표회 논문집
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• pp.258-265
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• 2002

Most structures are expected deform nonlinear and inelastic behavior when subjected to strong ground motion. Nonlinear time history analysis(NTHA) is the most rigorous procedure to compute seismic performance in the various inelastic analysis methods. But nonlinear analysis procedures necessitate more reliable and practical tools for predicting seismic behavior of structures. Some building codes propose the capacity spectrum method. This method is the concept of an equivalent linear system, wherein a linear system having reduced stiffness and increased damping is used to estimate the response of the nonlinear system. This procedure are conceptually simple, but the iterative procedure is time-consuming and may sometimes lead to no solution or multiple solutions. This paper presents a nonlinear direct spectrum method(NDSM) to evaluate seismic performance of structures, without iterative computations, given by the structural initial elastic period and yield strength from the pushover analysis, especially for mixed building structure.

• Steel and Composite Structures
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• 제31권3호
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• pp.243-259
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• 2019

This study deals with the nonlinear static analysis of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) truncated conical shells subjected to axial load based on the classical shell theory. Detailed studies for both nonlinear buckling and post-buckling behavior of truncated conical shells. The truncated conical shells are reinforced by single-walled carbon nanotubes which alter according to linear functions of the shell thickness. The nonlinear equations are solved by both the Airy stress function and Galerkin method based on the classical shell theory. In numerical results, the influences of various types of distribution and volume fractions of carbon nanotubes, geometrical parameters, elastic foundations on the nonlinear buckling and post-buckling behavior of FG-CNTRC truncated conical shells are presented. The proposed results are validated by comparing with other authors.

• Structural Engineering and Mechanics
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• 제58권3호
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• pp.515-532
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• 2016

The elastoplastic response of functionally graded material (FGM) beams resting on a nonlinear elastic foundation to an eccentric axial load is investigated by using the finite element method. The FGM is assumed to be formed from ceramic and metal phases with their volume fraction vary in the thickness direction by a power-law function. A bilinear elastoplastic behavior is assumed for the metallic phase, and the effective elastoplastic properties of the FGM are evaluated by Tamura-Tomota-Ozawa (TTO) model. Based on the classical beam theory, a nonlinear finite beam element taking the shift in the neutral axis position into account is formulated and employed in the investigation. An incremental-iterative procedure in combination with the arc-length control method is employed in computing the equilibrium paths of the beams. The validation of the formulated element is confirmed by comparing the equilibrium paths obtained by using the present element and the one available in the literature. The numerical results show that the elastoplastic post-buckling of the FGM beams is unstable, and the post-buckling strength is higher for the beams associated with a higher ceramic content. Different from homogeneous beams, yielding in the FGM beam occurs in the layer near the ceramic layer before in the layer near metal surface. A parametric study is carried out to highlight the effect of the material distribution, foundation support and eccentric ratio on the elastoplastic response of the beams.

• 한국강구조학회 논문집
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• 제13권6호
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• pp.661-672
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• 2001

본 연구는 Arc-length method를 이용한 복합재료 공간 구조물의 대변형 거동의 관찰에 관한 것이다. 비선형 평형경로의 각각의 하중단계에서 자동적으로 Arc-length 크기를 변화시켜 하중-변위 관계곡선을 추적할 수 있도록 하였다. 복합재료 공간 트러스의 점탄성 해석은 quasi-elastic 방법을 사용해 탄성해를 구하였다. Micro Mechanical Materials Modeling 방법을 사용하여 탄성계수를 결정하였고 하중조합에 따른 비선형 하중-변위 곡선을 추적하였다. 본 연구의 효과를 검증하기 위하여 그물형 공간 트러스를 다른 방법의 결과들과 비교하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.812-815
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• 2002

The shape of K-R curve for an ideally brittle material is flat because the surface energy is an unvaried material property. However, the K-R curve can take on a variety of shapes when nonlinear material behavior accompanies fracture. By the way, a general metallic material is nonlinear, structural steel is such. Therefore, the J-R curve form J-integral value instead of K parameters can be used to evaluate elastic-plastic materials with flaws in terms of ductile fracture that can be significant to design. In this paper, R-curve behaviors form K and J parameter is considered for the precise assessment of fracture analysis, in case of JS-SS400 steels.

• Steel and Composite Structures
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• 제7권5호
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• pp.355-376
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• 2007

The purpose of this study is to predict and investigate the time-dependent creep behavior of composite materials. For this, firstly the evaluation method for the modulus of elasticity of whole fiber and matrix is presented from the limited information on fiber volume fraction using the singular value decomposition method. Then, the effects of fiber volume fraction on modulus of elasticity of GFRP are verified. Also, as a creep model, the nonlinear curve fitting method based on the Marquardt algorithm is proposed. Using the existing Findley's power creep model and the proposed creep model, the effect of fiber volume fraction on the nonlinear creep behavior of composite materials is verified. Then, for the time-dependent analysis of a composite material subjected to uniaxial tension and simple shear loadings, a user-provided subroutine UMAT is developed to run within ABAQUS. Finally, the creep behavior of center loaded beam structure is investigated using the Hermitian beam elements with shear deformation effect and with time-dependent elastic and shear moduli.