• Proceedings of the KAIS Fall Conference
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• 2010.11b
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• pp.634-637
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• 2010

본 논문은 미세구조의 마이크로 액추에이터의 구동해석을 위한 결과로써 3차원 유한요소해석(Finite Element Analysis, FEA)을 이용하여 수행하였다. 마이크로머신과 같은 미소구조물을 해석하는 경우, 컴퓨터의 메인 프로세스에 비해 프리프로세서(pre-processor)의 비중이 높아지고 있어 그 효율화가 가장 중요하다. 수작업에 의존해야 했던 지난날의 요소분할법 기술은 최근에 들어 여러 연구자들에 의해 개발되고 있다. 특히, 복합현상을 다루는 정전 액추에이터에 직접적인 적용에 다소 어려움이 있는데 3차원적인 수치 및 실험평가는 실용적인 문제에서 비추어 볼 때 매우 중요하다. 따라서 본 논문에서는 센서로서의 역할을 하는 마이크로 정전 액추에이터의 기본설계를 위한 토대를 구축하고자 3차원적인 FEA 시뮬레이션을 수행하여 미세 회전운동을 분석하였다. 그 결과 설계된 모델에서 먼저 자중해석과 Mode 해석에서 기준치를 모두 만족하였다. 또한 설계된 액추에이터의 형상에 따른 회전자의 변형해석을 수행하여 시작토오크와 탄성한계까지의 위치제어에 필요한 회전각을 구하였으며, 정전장 해석을 통하여 시작토오크는 전압 $V^2$에 비례함을 알 수 있었다.

• Tribology and Lubricants
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• v.13 no.4
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• pp.18-25
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• 1997

The various deformation and fracture behaviors under light loads in soda-lime glass under sliding Vickers indentation have been studied. In soda-lime glass, deformation and fracture behaviors can be classified into four different patterns by applied load. At very light load (<0.1N), plastic deformation only occurred. At low loads (0.1~0.8N), median crack, appear. At intermediate loads (0.8~3.0N), median and lateral cracking occurred leading to a large chipping. At high loads (3.0~6.0N), a crushed zone was observed with median crack. The friction experiment finds that the increasing in the friction coefficients coincides with the onset of crushing in soda-lime glass.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.286-300
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• 2006

Nonlinear cross-anisotropic properties of soil is critical for exact numerical simulation. Theoretically, initial cross-anisotropic properties can be evaluated from triaxial tests with bender element tests, and nonlinear cross-anisotropic properties over initial strain level cannot be evaluated from triaxial tests. In this study, a supposed condition among nonlinear cross-anisotropic properties is suggested to calculate nonlinear cross-anisotropic properties from triaxial tests. Maximum strain and incremental strain energy are applied to combine triaxial test results and theoretical normalized shear modulus curve, respectively Based on combined results, nonlinear cross-anisotropic properties are calculated. Numerical simulation for triaxial tests Is carried out to verify the applicability of the supposed condition with calculated cross-anisotropic properties and simplified nonlinear cross-anisotropic model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.402-407
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• 1995

The effects of room temperature and strain aging treatment are discussed on the critical condition for the onset of growth of non-propagating cracks on 0.15% C low carbon steel, with special emphasis on the length of the critical non-propagating crack and on the crack opening displacement(COD) at the crack tip. It is found from the experimental analysis that room temperature and strain aging of a fatigue pre-cracked specimen introduced the closure of a crack tip of the pre-crack and the reduction of crack opening displacement at the wake of crack, together with an improvement in crack growth resistance of the microstructure. This may cause an increase in the endurance limit of the specimen, through the enhancement of effective stress for the onset of growth of the critical non-propagating crack.

• Journal of Power System Engineering
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• v.15 no.6
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• pp.47-52
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• 2011

In this study, an accurate 2-noded hybrid-mixed element for continuous fiber-reinforced laminated beams is newly proposed. The present element including the effect of shear deformation is based on Hellinger-Reissner variational principle, and introduces additional consistent node less degrees for displacement field interpolation in order to enhance the numerical performance. The micromechanical and lamination theory are employed in the finite element description to consider the effects of the laminate stacking sequences, material orthotropy, and fiber volume fraction, etc. The element stiffness matrix can be explicitly derived through the stationary condition and static condensation using Mathematica program. Several numerical examples confirm the accuracy of the present hybrid-mixed element and also show in detail the effects of the continuous fiber volume fraction, stacking sequences and boundary condition on the bending behavior of laminated beams.

• The Korean Journal of Rheology
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• v.2 no.1
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• pp.67-78
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• 1990

세라믹 분말의 사출성형성을 평가하기 위하여 다양한 혼합체 시스템에 대한 혼합도 와 유변학적 성질을 질화규소 미세분말의 부피비를 변화시키면서 조사하였다. 열가소성 결 합체 시스템은 폴리에틸린 폴리에틸렌 왁스 그리고 미소량의 첨가제를 혼합하여 사용하였 다. 혼합성능을 평가하기 위하여 비분산혼합에서는 총접촉면적비를 그리고 분산혼합에서는 총파괴표면적비를 혼합척도로서 사용하여 정성적으로 모형화하였다. 사용된 혼합기내의 유 동장을 해석하기 위하여 뉴우톤유체를 가정하여 유동해석을 수행하였다. 혼합물의 혼합도는 각각 5분 30분 동안 혼합된 시편을 주사전자현미경 사진에 의해 관찰하여 평가하였다. 또한 혼합물의 사출성형성 그리고 혼합질 점도 토우크 곡선 사이의 관계를 규명하기 위하여 전단 변형를 속도를 따른 점도를 모세관 점도계를 사용하여 측정하였으며 질화규소의 부피비가 60%일 때까지는 만족할 만한 성형성과 혼합질을 가짐을 알 수 있었다.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.139-146
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• 2001

Undrained triaxial tests were peformed for a weathered soil, which includes local measurement using LVDT The behavior from small In large strain conditions could be evaluated consistently through a triaxial test, The stress-strain relationship of undisturbed samples were compared with the disturbed and the shear moduli in the small strain level had the almost same values. Especially the shear moduli were mostly affected by the initial condition of water contents. An anisotropic hardening model based on the total stress concept could predict the stress-strain relationship accurately, which makes it possible to analyze the geotechnical problem reasonably for the weathered soil.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.368-371
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• 2008

An extensometer system to measure strain and displacement of cylindrical fatigue specimen in a autoclave of high temperature and high pressure environment has been developed by KEPRI. The extensometer reads the displacement caused by fatigue loads at the target length of the specimen installed inside the autoclave. The performance of the extensometer were tested at 15MPa, $315^{\circ}C$ of a operating pressurized water reactor. Two LVDT's of magnet type were connected to the extensometer and used for converting the fatigue displacement to electronic signal. The device is being used for developing environmental fatigue curve of CF8M cast austenitic stainless steel (CASS) in the test condition of low cycle and low strain. This paper introduces the background and results of the development.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.668-673
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• 2008

In this paper, we developed a physically-based micromechanical model for inelastic deformation of ceramic powders. The aggregate response of ceramic particles was modeled using the two-surface yield function which considered the shear-induced dilatancy caused by friction, rolling resistance and cohesion between powder particles and consolidation caused by plastic deformation of powder themselves under high compression. The constitutive equations were implemented into the user-subroutine VUMAT of finite element program ABAQUS/Explicit. The material parameters in the constitutive model were identified by calibrating the model to reproduce data from triaxial compression tests and simple compression tests. The density distribution obtained by using the proposed model was in good quantitative agreement with the experimental results of the triaxial compression and cold isostaic compression as well.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.293-294
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• 2006

The conventional strain measuring device is costly and complicated - it is not simple to understand its structure. Hence, strain gage and the A/D converter are assembled to come up with a load and a strain measuring device. The device was tested for measuring the strain in a loaded specimen and the experimental results were compared to those obtained by a commercial strain indicator.