• Composites Research
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• v.30 no.3
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• pp.193-201
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• 2017

Molecular dynamics simulation and the Mori-Tanaka micromechanics study are performed to investigate the effect of the covalent grafting between CNT and polyester on the mechanical behavior and load transfer of nanocomposites. The transversely isotropic stress-strain curves are determined through the tension and shear simulations according to the covalent grafting. Also, isotropic properties of randomly dispersed nanocomposites are obtained by orientation averaging the transversely isotropic stiffness matrix. By addressing the grafting, the transverse Young's modulus and shear moduli of the nanocomposites are improved, while the longitudinal Young's modulus decreases due to the degradation of the grafted CNT.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.5
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• pp.63-68
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• 2004

This paper presents a design of 12㎓ VCBRO(voltage controlled dielectric resonator oscillator) using a novel PBG(photonic band gap) ground plane and a varactor circuit that enhances the frequency linearity of VCO with different bias to varactors. The PBG structures are used for suppressing the second and third harmonics without any filters. To simulate the accurate resonating frequency, a DR coupled with microstrip lines is analysed by FTM(finite element method) simulation, and the results are transformed into scattering parameters to design the VCO. Some measured results are presented to show the usefulness of the proposed techniques.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.12
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• pp.1706-1711
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• 2013

This paper presents the filter of a resonator comprising a shorted open gap ring(SOGR) and interdigital lines. The proposed filter has the ultra wideband characteristic operating from 3 GHz to 10.5 GHz. In order to achieve the remarkable improvement in the size-reduction of the overall filter structure, only one cell of the SOGR with the inter-digital lines is adopted. It is shown that this filter has the size of $18mm{\times}15mm$ using a metamaterial, the fractional bandwidth over 100%, the insertion loss much less than 1dB, an acceptable return loss performance in the results.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.2
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• pp.162-168
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• 2011

In this research, nitrogen plasma source ion implantation(PSII) of non-coated tungsten carbide endmill tools was conducted with low heat treatment for increasing wear resistance. After the low heat treatment of PSIIed tools to give a homogeneity of wear resistance, the surface modification of tools was analyzed by hardness test, surface roughness and cutting forces. As for the resultant cutting forces, low heat treatment in temperature of $400^{\circ}C$ and $500^{\circ}C$ is stable because of low cutting resistance. The 20-minutes heat treated tool at spindle speed 25000rpm has superiority of surface roughness, Ra of $0.420{\mu}m$ and was found to have good wear resistance. The higher hardness value was obtained by increasing temperature from $300^{\circ}C$ to $600^{\circ}C$ for PSIIed tools with low heat treatment. As the PSIIed tools under 10minutes at temperature of $600^{\circ}C$ have the highest hardness as Hv of 2349.8, It was analyzed that temperature processing give much influences on hardness.

• Journal of the Korean Society of Clothing and Textiles
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• v.26 no.12
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• pp.1685-1693
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• 2002

다양한 용도로 사용되고 있는 라미네 이 팅 직물은 주로 별도로 제조된 고분자 필름 또는 막을 접착제, 열, 압력 등을 이용하여 기포(基布)와 결합시키는 방법으로 제조되어 진다. 이축연신시킨 Poly(tetrafluoroethylene) (PTFE) sheet는 매우 우수한 높은 투과성을 지니는 다공성 물질이 며, 본 연구에서는 이 막을 나일론 직물에 라미네이팅시킨 투습방수직물을 시료로 사용하여 라미네이팅 후의 역학특성 변화를 분석 하였다. 라미네이팅에 따른 투습방수직물의 물성과 역학특성의 변화에 관하여 살펴본 결과 다음과 같은 결과를 얻었다. 3-layer 라미네이팅 직물(base fabric-PTFE membrane-knitted lining)의 인열강도는 2-layer라미네이팅 직물 (base fabric-PTFE membrane)에 비해 매우 높게 나타났으며, 가공 전 직물과 비교하여 코팅직물에서 나타난 것과 같은 인열강도의 감소는 나타나지 않았다. 직물-PTFE 막 복합체 의 경우, 라미네 이 팅 이 파단강도 및 파단신도 의 증가에 기여 한 것으로 나타났으며 특히 3-layer 라미네이팅 직물의 경우, 신장률이 20%를 넘어서면서 강도가 현저히 증가하였다. 의복을 착용하였을 때 가해질 수 있을 정도의 소변형(small deformation) 하에서의 역학특성 에 있어서는 라미네이팅에 의해 전단특성이 가장 유의한 변화를 나타내었다. 전단강성(G)과 전단 히스테리시스 (2HG,2HG5)모두 증가하였고, primary hand value 중에서는 stiffness 가장 현저한 증가를 나타내었다

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.649-652
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• 2008

In this paper, the applicability of hwangtoh, as an alternative of cement paste, is investigated for the solution of internal heat and shrinkage caused by the hydration of cement paste. Several small-sized specimens of hwangtoh and ordinary portland concrete(OPC) were compared as to compressive strength, heat of hydration, and shrinkage strain. Moreover, the applicability of mass structure was reviewed through the test of large-size specimens. The 28-day compressive strength of hwangtoh concrete(HBC), ranged 18 to 33 Mpa, can reach that of ordinary portland concrete. Not only the maximin internal temperature of HBC was read about 1/4 of OPC as it is cured, but also its drying shrinkage decreased as lower as 50% of OPC starting from 60 days. Therefore, hwangtoh binder is more favorable than cement one in the view of hydration heat and shrinkage under the construction of mass structures.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.409-412
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• 2010

본 연구는 목조 건축물 흙벽의 수평가력실험 결과를 이용한 내진성능 평가를 목적으로 한다. 흙벽 실험시험체는 기둥과 보 결합방식에 따라 민도리, 초익공, 장여방식으로 분류되고 벽체 형태에 따라 창문, 문, 전면 벽체, 인방 부재수 등으로 계획을 하였다. 12개 흙벽 시험체의 가력결과, 전면 벽체 시험체는 변위각 1/30에서 가장 큰 강성 저하율을 보이며 중인방과 수직재가 있는 벽체는 에너지 소산능력이 가장 큰 것으로 나타났다. 기존 연구로부터 목조 건축물 항복점 평가방법을 이용하여 등가탄소성 곡선으로 나타낸 전단내력은 민도리방식이 프레임과 전면 벽체일 경우 가장 크고, 전단응력은 벽체 개구율에 따라 다르게 나타났다. 실험결과로부터 적용 대상 건축물의 X, Y방향 구조성능을 산출하고 구조내진지표와 역량스펙트럼을 이용하여 내진성능 평가를 실시한 결과, 대상 목조 건축물은 내진성이 있음으로 평가되었다.

• Aerospace Engineering and Technology
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• v.10 no.2
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• pp.94-100
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• 2011

In this paper, an assessment on the preliminary coupled load analysis results for advanced Low Earth Orbit Earth Observation satellite was performed. Spacecraft FE-model was converted into Craig-Bampton model consisting of mass matrix, stiffness matrix, acceleration transformation matrix, displacement transformation matrix, and it was delivered to the launch vehicle developer. Launch vehicle developer performed a coupled load analysis with launch vehicle model and spacecraft Craig-Bampton model, and the coupled load analysis results were provided to us. From the assessment on the analysis results, it was verified that spacecraft is safe under launch environment.

• The Journal of the Acoustical Society of Korea
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• v.16 no.1
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• pp.76-80
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• 1997

Acoustic resonance characteristics were analyzed and their effect on the refrigerating capability were experimentally verified on a fabricated Hofler-type thermoacoustic refrigerating system. Factors governing the overall resonance are the resonator composed of a cavity and two pipes, the loudspeaker driving the resonator, and rear side impedance characteristics of speaker housing. All these are coupled with electric constants of the speaker to exhibit electric resonance. Also the 'wall-effect' within the resonator causes attenuation to reduce the sharpness of the resonance. Analysis and experiments showed housing and the wall-effect of the resonator reduce the sharpness of resonance. Maintaining the accuracy of the resonance is, therefore, very important for efficient refrigeration.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.7
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• pp.139-148
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• 1998

Internal and external heat sources will cause to deform to machine elements in the contact joint of structure, which results in the change of contact pressure distribution different from initial assembly. Heat induced variations of contact pressure will change the static and dynamic properties such as contact stiffness, damping as well as contact heat conduction in the structure In order to design and control the intelligent machine tool operating in variant conditions more sophisticatedly, the good prediction for the changes of prescribed properties are strongly required especially in the contact elements adjacent to the rotational or linear bearing. This paper presents some computational and experimental results in regard to static and dynamic characteristics of the press-fitted bush and shaft assembly which is a model of the bearing innerrace and shaft assembly. In the condition of heat generation on the outer surface of the bush, the effects of changes in the negative clearance and the heat flux on pressure distribution and dynamic properties are investigated. Results of this study show that the edge effect of the bush and the initial clearance have effects on the transient dynamic characteristics significantly.