• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04b
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• pp.281-286
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• 1993

Projection TV에는 시각 품질을 최종적으로 표시하는 디스플레이 소자인 비구면플라스틱 렌즈를 적용하고 있으나 전량 일본에서 완제품으로 공급 받고 있다. 플라스틱 비구면 렌즈를 성형하기 위해서는 사출 공정에 대한 철저한 이해 와 폴리머의 광탄성 거동에 대한 개념이 핵심이라고 말할 수 있다. 복굴절성 실험은 폴리머의 유변학적 거동을 파악 하는데있어 가장 유용한 실험중의 하나이다. 본 글에서는 이와 관련된 사항인 복굴절성, 잔류 응력 형성 메카니즘, 밀도이완 작용의 상관관계와 비구면 렌즈의 성형 조건 및 공정에대해 기술 하였고, 또한 측정된 수지데이타를 이용 상용 S/W를 사용하여 유동, 냉각, 보압 ( 압축) 및 수축 해석을 실시 하여 각 stage에서 경험한 온도 와 압력의 이력에따라 변화하는 열 응력에 기인한 잔류 응력 계산 Pg을 개발 상용 S/W 와 비교 검증 하였다.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.303-315
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• 2000

The main object of this study is to analyze mechanical behaviors as anisotropic three-dimensional body under various static loads. This paper presents the applicability of the finite difference method to three dimensional problem of anisotropic body. The finite difference method as applied here is generalized to anisotropic three-dimensional problem of elastic body where the governing differential equations of equilibrium of such bodies are expressed in terms of the displacement u, v, and w in the coordinates axes x, y and z, care being taken to modify the finite difference expressions to satisfy the appropriate boundary conditions. By adopting a new three dimensional finite difference modelling including elimination of pivotal difference points in the case of free boundary condition, the three dimensional problem of anisotropic body was successfully completed. Several numerical results show quick convergence and numerical validity of finite difference technique in three dimensional problem.

• Journal of the Microelectronics and Packaging Society
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• v.10 no.4
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• pp.1-8
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• 2003

Thermo-mechanical behavior of a ceramic ball grid array (CBGA) package assembly are characterized by high sensitive moire interferometry. Moir fringe patterns are recorded and analyzed at various temperatures in a temperature cycle. Thermal-history dependent analyses of global and local deformations are presented, and bending deformation (warpage) of the package and shear strain in the rightmost solder ball are discussed. A significant non-linear global behavior is documented due to stress relaxation at high temperature. Analysis of the solder interconnections reveals that inelastic deformation accumulates on only eutectic solder fillet region at high temperatures.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.157-160
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• 2009

멀티 피직스 시스템은 구동을 수치적으로 해석하기 위하여 두 개 이상의 연성이 되어 있는 물리계를 고려해야하는 시스템을 일컫는다. 대표적인 예로 기계 분야에서 현재까지 많이 연구되어 왔던 열탄성(Thermal/Structure)과 유체/구조 연성(Fluid/Structure)시스템을 들 수 있다. 또한 현재 차세대 성장산업으로 많은 관심이 집중되고 있는 의료기기나 지능형 자동차와 로봇 등에서 사용되는 다양한 센서와 엑추에이터 등도 특별한 예로 들 수 있다. 특히, 한 개의 물리계 해석으로 시스템 해석이 가능한 기존의 일반적인 기계 시스템과는 달리 MEMS 등의 초소형 시스템은 시스템의 거동을 수치적으로 계산하기 위하여 여러 물리계의 연성을 고려해야 한다는 점에서 대표적인 다물리계 시스템의 예로 들 수 있다. 이렇게 우리생활에 밀접하게 쓰이고 있는 멀티 피직스 시스템은 단일 물리계 시스템과 비교하여 엔지니어의 경험에 의존하여 설계(Design)하기가 어려운 특성이 있다. 이에 이 연구 논문에서는 이런 멀티 피직스 시스템을 해석하고 최적화 하기위한 노력을 소개한다.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.3
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• pp.89-95
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• 1997

A simulation to investigate the thermal behavior in short fiber or whisker reinforced composite materials has been performed for the application to the thermoelastic stress analysis using Finite Element Method (FEM). To obtain the internal field quantities of composite material, the procedure of micromechanical modeling and the principle of virtual work were implemented. For the numerical illustration, an aligned axisymmetric single fiber model has been employed to assess field quantities. It was found that the proposed simulation methodology for thermoelastic stress analysis is applicable to the complicated inhomogeneous solid for the investigation of micromechanical thermoelastic behavior.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1083-1089
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• 2010

Shape memory alloys (SMAs) are smart materials. The unique characteristics of SMAs enable the production of large force and displacement. Hence, SMAs can be used in many applications such as in actuators and active structural acoustic controllers; the SMAs can also be used for dynamic tuning and shape control. A SMA torque tube actuator consisting of SMA tubes and superelastic springs is proposed, and the behaviors of the actuator are investigated. From the results of heat transfer analysis, it is proved that the SMA torque tube actuator with both resistive heating of SMA itself and a separate conventional heating rod in the tube core has good performance. The behavior of an actuator system was analyzed by performing a contact analysis, and the twisting motion was noticed when checking the actuation. 3D SMA nonlinear constitutive equations were formulated numerically and implemented by performing a nonlinear analysis by using Abaqus UMAT.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.2
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• pp.92-98
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• 2017

Porosity in polymer matrix composites generated during pyrolysis process affect the thermomechanical behavior of the composites. In this paper, multislice finite element models for the porous composite materials are developed, and poroelastic and failure analysis for these models are performed. In order to investigate the three-dimensional effects, finite element meshes are modeled considering different porosity(up to 0.5) and the number of slices (up to five). As a result, effective Young's moduli and poroelastic parameters exhibit the maximum differences of 74.0% and 442.1% with respect to porosity respectively, and 98.7% and 37.2% with respect to the number of slices. First and last failure strengths are decreased 88.2% and 90.0% with respect to porosity respectively, and 53.8% and 171.8% with respect to the number of slices.

• Journal of Aerospace System Engineering
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• v.18 no.1
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• pp.1-10
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• 2024

In a previous study, a structure of a superplastic yoke consisting of a thin FR4 layer laminated with viscoelastic tape on both sides of a shape memory alloy (SMA) was proposed to reduce residual vibration generated by a deployable solar panel during high motion of a satellite. Damping properties of viscoelastic tapes will change with temperature, which can directly affect vibration reduction performance of the yoke. To check damping performance of the yoke at different temperatures, free damping tests were performed under various temperature conditions to identify the temperature range where the damping performance was maximized. Based on above temperature test results, this paper predicts temperature of the yoke through orbital thermal analysis so that the yoke can have effective damping performance even if it is exposed to an orbital thermal environment. In addition, the thermal design method was described so that the yoke could have optimal vibration reduction performance.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.627-636
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• 2011

Recently, to prevent explosive spalling of high-strength concrete (HSC) members, the usage of nylon fiber instead of polypropylene fiber has increased. Past experimental studies have been conducted to examine the spalling and mechanical properties of HSC with nylon fibers when exposed to elevated temperature. However, the previous studies on HSC with nylon fibers subjected to high temperatures were performed only on the properties such as spalling, compressive strength, and elastic modulus rather than investigations on to the behaviors such as thermal strain, total strain, steady state creep, and transient creep. Therefore, in this study thermal strain, total strain, steady state creep, and transient creep of HSC mixed with nylon fibers with water to binder ratio of 0.30 to 0.15 were tested. The experimental results showed that nylon fibers did not affect the performance of HSC with nylon fibers at high temperatures. However, HSC with nylon fibers generated a larger transient creep strain than that of HSC without fibers and normal strength concrete.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.7 s.100
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• pp.836-842
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• 2005

Nonlinear dynamic characteristics of active piezolaminated plates are investigated with respect to the thermopiezoelastic behaviors. For largely deformed structures with small strain, the incremental total Lagrangian formulation is presented based on the virtual work principles. A multi-field layer-wise finite shell element is proposed for assuring high accuracy and non-linearity of displacement, electric and thermal fields. For dynamic consideration of thermopiezoelastic snap-through phenomena, the implicit Newmark's scheme with the Newton-Raphson iteration is implemented for the transient response of various piezolaminated models with symmetric or eccentric active layers. The bifurcate thermal buckling of symmetric structural models is first investigated and the characteristics of piezoelectric active responses are studied for finding snap-through piezoelectric potentials and the load-path tracking map. The thermoelastic stable and unstable postbuckling, thermopiezoelastic snap-through phenomena with several attractors are proved using the nonlinear time responses for various initial conditions and damping loss factors. Present results show that thermopiezoelastic snap-through phenomena can result in the difficulty of buckling and postbuckling control of intelligent structures.