• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.135-138
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• 2002

The purpose of this study is to investigate the lubricated wear properties of Saffil/Al, Saffil/$Al_2O_3/Al$ and Saffil/SiC/Al hybrid metal matrix composites fabricated by squeeze casting method. Wear tests were done on a pin-on-disk friction & wear tester with long sliding distance. The wear properties of the three composites were evaluated in many respects. The effects of Saffil, $Al_2O_3$ particles and SiC particles on the wear behavior of the composites under lubricated conditions were elucidated. Wear mechanisms were analyzed by observing the worn surfaces of the composites. The variation of coefficient of friction (COF) during the wear process was recorded by using a computer. Comparing with the dry sliding condition, all three composites showed excellent wear resistance when lubricated by liquid paraffin. Under intermediate load, Saffil/Al showed best wear resistance among them, and its COF value is the smallest. The dominant wear mechanism of the composites was microploughing, but microcracking also occurred for them to different extent.

• 한국생활과학회지
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• 제24권2호
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• pp.285-295
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• 2015

To identify optimized thermal properties of mold brassiere cup for improved thermal comfort during summer, we compared the thermal resistance and the water vapor permeability of Polyurethane (PU) foam, 3D spacer fabric and the two combined materials of the PU foam and the 3D spacer fabric. Four experimental mold brassieres were made of the materials for wearing test. Six women in their twenties evaluated the wearing sensation in the hot and humid environment. The changes in microclimate temperature and humidity while wearing test brassiere cups were measured. Results indicate that thermal resistance increased as more PU foam were combined, while the water vapor permeability was higher as the content of the 3D spacer fabric increased at thickness of 18mm and over. However, in the wear test, the PU foam brassiere was the most preferred in all ambient conditions due to its soft, flexible and smooth texture, despite its high thermal resistance and low water vapor permeability. This indicates that the textures of mold foams are more dominant properties than thermal properties for mold foams in determining the wear comfort of mold brassieres.

• 한국염색가공학회지
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• 제26권3호
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• pp.218-229
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• 2014

The wearing comfort of garment is governed by two kinds of characteristics such as moisture and thermal transport properties and mechanical properties of fabrics. The porosity influenced by yarn and fabric structural parameters is known as main factor for wearing comfort of garment related to the moisture and thermal transport properties. This study investigated effect of porosity of composite yarns to the moisture and thermal comfort properties of composite fabrics made of hollow composite DTY and ATY yarns. The theoretical porosity and pore size were inversely proportional to cover factor of fabric, but cover factor was not correlated with experimental pore size. The wicking property of hydrophobic PET filament fabric showed inferior result irrespective of porosity, pore size and cover factor. The drying rate was superior at composite fabrics with high pore size and low cover factor, and pore size was dominant factor for drying property. On the other hand, thermal conductivity of composite fabric was mainly influenced by cover factor and not influenced by porosity. Air permeability was influenced by both porosity and cover factor and was highly increased with increasing porosity and decreasing fabric cover factor.

• 천문학논총
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• 제30권2호
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• pp.521-523
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• 2015

The Milky Way did not form in isolation, but is the product of a complex evolution of generations of mergers, collapses, star formation, supernovae and collisional heating, radiative and collisional cooling, and ejected nucleosynthesis. Moreover, all of this occurs in the context of the cosmic expansion, the formation of cosmic filaments, dark-matter haloes, spiral density waves, and emerging dark energy. This paper summarizes a review of recent attempts to reconstruct this complex evolution. We compare simulated properties with various observed properties of the Local Group. Among the generic features of simulated systems is the tendency for galactic halos to form within the dark matter filaments that define a supergalactic plane. Gravitational interaction along this structure leads to a streaming flow toward the two dominant galaxies in the cluster. We analyze this alignment and streaming flow and compare with the observed properties of Local-Group galaxies. Our comparison with Local Group properties suggests that some dwarf galaxies in the Local Group are part of a local streaming flow. These simulations also suggest that a significant fraction of the Galactic halo formed at large distances and arrived later along these streaming flows.

• 소음진동
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• 제9권2호
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• pp.317-323
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• 1999

Dynamic characteristics of catenary that supplies electrical power to high-speed trains are investigated. A simple catenary is composed of the contact and messenger wires connected by droppers possessing bi-directional stiffness properties. For slender, repeating structures such as catenary, both the wave propagation and vibration properties need to be understood. The influence of parameters that determine catenary dynamics are investiaged through numerical simulations involving finite element models. The effects of the tension and flexural rigidity of the contact wire is first investigated. The effects of dropper characteristics are then investigated. For linear droppers wave propagation as well as modal properties are determined. For large catenary motion, droppers can be modeled as bi-directional elements possessing low stiffness in compression and high stiffness in tension. For this case, impulse response is computed and compared with the cases of linear droppers. It is found that the catenary dynamics are primarily determined by contact wire tension and dropper properties, with large responses observed in 5∼40 Hz frequency range. In particular, the dropper stiffness and spacing are found to have dominant influence on the response frequency and the wave transmission characteristics.

• Composites Research
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• 제23권3호
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• pp.37-42
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• 2010

섬유 방향 강성과 강도는 복합재 압력 용기의 성능과 밀접한 관계를 갖기 때문에, 압력 용기 구조 설계시에 다른 물성들보다 중요 설계 인자가 된다. 즉 복합재 압력 용기의 내압 변형 및 파열 압력은 섬유 물성에 의해 큰 영향을 받는다. 그러므로 정확한 섬유 방향 물성을 측정할 수 있는 기법을 확립하는 것이 복합재 압력 용기 설계 전에 우선되어야 한다. 그러나 복합재 압력용기의 섬유 방향 물성은 제작 공정 변수(와인딩 장비, 작업자, 작업환경 등)와 크기 효과에 의해 큰 영향을 받으므로 기존의 시편 시험 방법으로는 정확한 섬유 방향 물성 측정이 어렵다. 섬유 물성을 측정하는 가장 이상적인 시험 방법은 실물 압력용기 파괴시험이지만 많은 비용이 소요되어, 제품으로부터 다량의 링 시편을 채취, 내압 시험을 할 수 있는 Hoop ring 시험 방법이 제시되었다. Hoop ring 시험과 실물 압력용기의 수압 파괴 시험으로부터 구한 섬유 방향 물성들은 근접된 좋은 일치를 나타내었다.

• 한국의류학회지
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• 제18권1호
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• pp.15-22
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• 1994

본 연구에서는 면시험포와 cellophane film을 이용하여 xenon arc lamp 를 사용한 인공기후조 안에서 광선의 파장에 따른 강도의 변화와 변색을 조사하였다. Pyrex와 quartz filter를 사용하여 광선의 파장이 섬유의 성질을 변화시키는 중요한 요인임을 밝히고 first-order kinetic model을 사용하여 반응속도를 측정하였다. 또 면섬유의 황변현상을 화학적으로분석하여 파장이 긴 자외선과 가시광선의 영역에서는 황변과 동시에 표백효과가 있음을 알게 되었고 그 속도를 측정하였다. 세가지의 중요한 말단기분석을 통해 carbonyl기의 양이 제일 많고 carboxyl기와 peroxide기도 존재함을 분석하였고 또 이들의 양은 온도와 습도에 따라 변화하는 것으로 나타났다 Cellulose chain의 중합도를 측정하고 이를 cellulose bond scission과 연결시켜서 중합도와 섬유의 강도저하와의 관계를 연구하였다.

• 한국결정성장학회지
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• 제14권6호
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• pp.233-235
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• 2004

Shaped single crystals of Bi : $Y_3Ga_5O_{12}$(Bi = 0.041, 0.047 and 0.061 mol%) were grown by the micro-pulling-down method. Optical absorption spectra show an absorption band at 288 nm ascribed to the lowest energy $6s^2$ \longrightarrow 6s6p transition of $Bi^{3+}$ , while luminescence spectra demonstrate the band at 314 nm ascribed to the reverse radiative transition of the excited $Bi^{3+}$ centres. At room temperature, dominant decay time component was found to be about 440 ns with a minor slower component 580 ns.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1995년도 봄 학술발표회 논문집
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• pp.45-52
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• 1995

The stability and integrity of precast large panel structures are analyzed with nonlinear mathematical model considering the inelastic properties of horizontal joints. In this research, an analysis for cyclic loading test was carried out by the macro model that idealized the horizontal joints as inelastic-nonlinear spring systems. As a results, the strain hardening ratio of shear slip element was estimated as about 0.05%- 0.2% of initial shear stiffness. And under lateral load, the rocking motion due ti overturning moment was dominant rather than shear slip motion in the behavior of precast structures.

• Composites Research
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• 제28권1호
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• pp.1-5
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• 2015

In this paper the influence of fiber orientation of basalt and carbon inter-ply fabrics on the flexural properties of hybrid composite laminates was experimentally investigated. Four types of basalt/carbon/epoxy inter-ply hybrid composite laminates with varying angle ply orientation of reinforced basalt fiber and fixed orientation of carbon fiber were fabricated using hand lay-up technique. Three point bending test was performed according to ASTM 7264. The fracture surface analysis was carried out by scanning electron microscope (SEM). The results obtained from the four laminates were compared. Lay-up pattern of $[0B/+30B/-30B/0C]_S$ exhibits the best properties in terms of flexural strength and flexural modulus. Scanning electron microscopy results on the fracture surface showed that the interfacial de-bonding between the fibers and epoxy resin is a dominant fracture mode for all fiber lay-up schemes.