• 한국분말재료학회지
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• 제20권4호
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• pp.269-274
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• 2013

The present work investigated the dispersion behavior of $Y_2O_3$ particles into AISI 316L SS manufactured using laser cladding technology. The starting particles were produced by high energy ball milling in 10 min for prealloying, which has a trapping effect and homogeneous dispersion of $Y_2O_3$ particles, followed by laser cladding using $CO_2$ laser source. The phase and crystal structures of the cladded alloys were examined by XRD, and the cross section was characterized using SEM. The detailed microstructure was also studied through FE-TEM. The results clearly indicated that as the amount of $Y_2O_3$ increased, micro-sized defects consisted of coarse $Y_2O_3$ were increased. It was also revealed that homogeneously distributed spherical precipitates were amorphous silicon oxides containing yttrium. This study represents much to a new technology for the manufacture and maintenance of ODS alloys.

• 한국방재학회 논문집
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• 제7권5호
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• pp.47-60
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• 2007

본 논문에서는 전단변형률과 회전관성을 고려한 준적합 쉘 요소를 이용한 점진기능재료 판과 쉘의 고유진동수와 좌굴하중을 연구하였다. S 형상 함수를 이용한 세라믹과 금속의체적요소의 변화에 따른 점진기능재료 판과 쉘의 고유치 문제를 연구하였다. 점진기능재료 쉘 요소의 면내 강성, 휨 강성 및 전단 강성의 수식은 등질 요소보다 복잡한 재료의 성질들로 결합되어 있다. 유한요소의 수치적 결과를 검정하기 위해 1차 전단변형 이론에 의한 직사각형 판의 Wavier해를 제시하였다. 적층복합 구조 및 S 형상 점진기능재료 구조의 수치해석해는 Navier의 해로 검증하였으며, S 형상 점진기능재료 구조물의 다양한 예제를 제시하였다. 해석결과는 Navier의 이론해와 아주 잘 일치함을 알 수 있었다.

• 한국재료학회지
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• 제12권8호
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• pp.641-649
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• 2002

The redox properties of a homogeneously-precipitated $TiO_2$ rutile powder with a BET surface area of ~$200 m^2$/g, consisting of an acicular primary particle, were characterized using photocatalytic reaction in aqueous 4-chlorophenol, Cu-EDTA and Pb-EDTA solutions under ultraviolet irradiation, compared to those of commercial P-25 X$200 m_2$ powder with a spherical primary particle as well as home-made anatase $TiO_2$ powder with ~$200 m^2$/g BET surface area. Here, the anatase powder also includes mainly the primary particles very similar to the acicular shapes of the rutile $TiO_2$ powder. The rutile powder showed the fastest decomposition rate and the largest amount in the photoredor, compared with the anatase or P-25 powder, while the anatase powder unexpectedly showed the slowest rate and the smallest amount in the same experiments regardless of almost the same surface area. From results, the excellent photoredox abilities of this rutile powder appears to be due to specific powder preparation method, like a homogeneous precipitation leading to direct crystallization from the solution, regardless of their crystalline structures even when having the similar particle shape and surface area.

• 한국결정성장학회지
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• 제2권1호
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• pp.20-29
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• 1992

전영역에 결쳐서 고용영역이 존재하는 $BaTiO_3-NaNbO_3$계에서, congruent melting composition인 $30BaTiO_3{cdot}70NaNbO_3$조성의 고용체 단결정을 Czochralski법에 의하여 육성하였다. 직경 15-50mm, 길이 20-30mm인 단결정이 결정인상속도 2.0mm/h, 결정회전수 5.0-1-rpm에서 육성되었다. 그러나 결정 육성중 육성되는 결정의 열전도도가 낮기 때문에, 발생하는 잠열(latent heat)의 방출이 충분치 않아 고-액계면이 평탄하게 유지되지 않았고 그결과로 육성된 결정중에는 corestructures가 관찰되었다. 육성된 결정에서 core 부분을 제외한 다른 부분은 inclusion등이 없는, 광학적으로 균질한 단결정이었고 가시광 영역에서 양호한 광투과율을 보였다.

• Wind and Structures
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• 제22권4호
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• pp.429-454
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• 2016

In this paper, a shear deformation plate theory based on neutral surface position is developed for free vibration analysis of functionally graded material (FGM) plates. The material properties of the FGM plates are assumed to vary through the thickness of the plate by a simple power-law distribution in terms of the volume fractions of the constituents. During manufacture, defects such as porosities can appear. It is therefore necessary to consider the vibration behavior of FG plates having porosities in this investigation. The proposed theory is based on assumption that the in-plane and transverse displacements consist of bending and shear components, in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments. The neutral surface position for a functionally graded plate which its material properties vary in the thickness direction is determined. The equation of motion for FG rectangular plates is obtained through Hamilton's principle. The closed form solutions are obtained by using Navier technique, and then fundamental frequencies are found by solving the results of eigenvalue problems. Numerical results are presented and the influences of the volume fraction index and porosity volume fraction on frequencies of FGM plates are clearly discussed.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.1452-1457
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• 2010

본 연구에서는 국내 회처리장에 매립되어 있는 매립회를 효율적으로 사용하기 위한 실내 모형시험장치인 CSP 시스템을 제작하여 매립회와 물 그리고 시멘트량을 조절하여 모형지반을 조성하고 이에 대한 강성변화를 평가하였다. 시멘트를 첨가한 모형지반이 시멘트를 첨가하지 않은 경우에 비해 빠른 속도로 경화가 진행되었으며 192시간 경과 후에는 경화속도가 급격히 감소하는 것으로 나타났다. 모형지반 조성시 전체 중량의 30~45% 사이의 물의 양 변화는 지반의 강성 변화에 큰 영향을 끼치지는 않는 것으로 나타났다. 추후에는 지반 조성 초기에 큰 지반강성의 크기를 얻을 수 있도록 시멘트량을 증가시키는 등의 다양한 영향인자에 대한 시험을 수행하여 고유동성 채움재 활용성을 정량적으로 평가하는 것이 필요할 것으로 판단된다.

• 천문학회지
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• 제48권1호
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• pp.75-82
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• 2015

We use a volume-limited sample of quasars in the Sloan Digital Sky Survey (SDSS) DR7 quasar catalog to identify quasar groups and address their statistical significance. This quasar sample has a uniform selection function on the sky and nearly a maximum possible contiguous volume that can be drawn from the DR7 catalog. Quasar groups are identified by using the Friend-of-Friend algorithm with a set of fixed comoving linking lengths. We find that the richness distribution of the richest 100 quasar groups or the size distribution of the largest 100 groups are statistically equivalent with those of randomly-distributed points with the same number density and sky coverage when groups are identified with the linking length of $70h^{-1}Mpc$. It is shown that the large-scale structures like the huge Large Quasar Group (U1.27) reported by Clowes et al. (2013) can be found with high probability even if quasars have no physical clustering, and does not challenge the initially homogeneous cosmological models. Our results are statistically more reliable than those of Nadathur (2013), where the test was made only for the largest quasar group. It is shown that the linking length should be smaller than $50h^{-1}Mpc$ in order for the quasar groups identified in the DR7 catalog not to be dominated by associations of quasars grouped by chance. We present 20 richest quasar groups identified with the linking length of $70h^{-1}Mpc$ for further analyses.

• 대한기계학회논문집A
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• 제41권2호
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• pp.81-85
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• 2017

섬유강화 고분자 복합재료는 섬유 형태의 강화제와 고분자 형태의 기지재료가 결합된 형태로 이는 무게 대비 고강도 및 고강성의 구조물 제작에 용이하다. 본 연구에서는 형상기억합금 와이어가 삽입된 섬유 강화 지능형 연성 복합재 구동기를 제작, 이의 재료 구성에 따른 거동 특성을 평가 하고자 한다. 구동기는 형상기억합금이 포함된 구동층과 일반 구조층으로 구성되어 한 층씩 적층되는 방식으로 제작되며 재료 구성에 따른 거동 특성을 살펴보기 위하여 일반 구조층으로 사용된 유리섬유 직물의 적층 수, 기지재료의 종류를 달리한 뒤 구동 특성을 살펴보았다. 또한, 구동 시에 요구되는 인가 전류의 양을 달리하여 최대 구동각과 최대 구동각에 도달하는 구동 시간을 측정하였다.

• Steel and Composite Structures
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• 제16권6호
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• pp.559-576
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• 2014

A new mathematical model and its finite element formulation for the non-linear stress-strain analysis of a planar beam strengthened with plates bolted or adhesively bonded to its lateral sides is presented. The connection between the layers is considered to be flexible in both the longitudinal and the transversal direction. The following assumptions are also adopted in the model: for each layer (i.e., the beam and the side plates) the geometrically linear and materially non-linear Bernoulli's beam theory is assumed, all of the layers are made of different homogeneous non-linear materials, the debonding of the beam from the side-plates due to, for example, a local buckling of the side plate, is prevented. The suitability of the theory is verified by the comparison of the present numerical results with experimental and numerical results from literature. The mechanical response arising from the theoretical model and its numerical formulation has been found realistic and the numerical model has been proven to be reliable and computationally effective. Finally, the present formulation is employed in the analysis of the effects of two different realizations of strengthening of a characteristic simply supported flexural beam (plates on the sides of the beam versus the tension-face plates). The analysis reveals that side plates efficiently enhance the bearing capacity of the flexural beam and can, in some cases, outperform the tensile-face plates in a lower loss of ductility, especially, if the connection between the beam and the side plates is sufficiently stiff.

• Wind and Structures
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• 제29권6호
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• pp.457-469
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• 2019

In this paper, a numerical solution is presented for supersonic flutter analysis of cantilever non-symmetric functionally graded (FG) sandwich plates. The plate is considered to be composed of two different functionally graded face sheets and an isotropic homogeneous core made of ceramic. Based on the first order shear deformation theory (FSDT) and linear piston theory, the set of governing equations and boundary conditions are derived. Dimensionless form of the governing equations and boundary conditions are derived and solved numerically using generalized differential quadrature method (GDQM) and critical velocity and flutter frequencies are calculated. For various values of the yaw angle, effect of different parameters like aspect ratio, thickness of the plate, power law indices and thickness of the core on the flutter boundaries are investigated. Numerical examples show that wings and tail fins with larger length and shorter width are more stable in supersonic flights. It is concluded for FG sandwich plates made of Al-Al₂O₃ that increase in volume fraction of ceramic (Al₂O₃) increases aeroelastic stability of the plate. Presented study confirms that improvement of aeroelastic behavior and weight of wings and tail fins of aircrafts are not consistent items. It is shown that value of the critical yaw angle depends on aspect ratio of the plate and other parameters including thickness and variation of properties have no considerable effect on it. Results of this paper can be used in design and analysis of wing and tail fin of supersonic airplanes.