• 자원환경지질
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• 제32권1호
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• pp.1-11
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• 1999

In the last decade, the supply of natural aggregates has been continuously increased due to the other types of aggregates. In general, aggregates constitute 70-80% of the total volume of concrete, so the quality of aggregates is main factor controlling physical characteristics of concrete. For this reason, physical properties of aggregate according to different rock types were studied. The majority of crushed aggregates is taken out of granite, gneiss, sandstone, andesite, basalt and so forth. The physical properties of these rock types were tested and most of them fell within the acceptable limit on the base of Korean standard regulation. The major lithology of the crushed aggregates is granite and gneiss, both of which are marked for more than 50% of total lithology thpes in Korea. A to the physical properties of granite, the high specific gravity coincides with low porosity, low absorption ratio, while the abrasion and soundness index show, in general, no specific trend. It has been assumed that slight differences of the physical properties of granite aggregates are related with those of the mineral composition, grain size, and so on. In comparison to granite, the physical properties of gneiss have little correlation one after another. This trend is related to different mineral composition, grain size and typical sheet fractures typically prevailing in the texture of gneiss. Spatial pattern of physical properties shows that high specific gravity of granite coincides only with low porosity and absorption ratio in all provinces except Cheolla province, and high specific gravity of gneiss coincides with low porosity and absorption ratio only in Cheolla and Gandwon provinces.

• 한국주조공학회지
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• 제18권3호
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• pp.254-261
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• 1998

Microstructure and mechanical properties of the low pressure die-cast Al wheels were investigated by microscope, image analyzer, NDT (non-destructive test), and tensile test. The variation of SDAS (secondary dendrite arm spacing), porosity per unit area, quality grade, and tensile properties with the mold temperatures were examined. SDAS was gradually decreased with a decrease in temperature. However, the lowest value of porosity per unit area was observed at the mold temperature of $405^{\circ}C$ and the optimum mold temperature was found to be $405^{\circ}C$. Besides, from the observation of pore morphology, it was also found that the pore formation was mainly caused by shrinkage during solidification. The tensile strength, elongation, and impact toughness were markedly decreased, however the yield strength was nearly constant. The decrease of mechanical properties is attributed to the increase of porosity.

• 한국대기환경학회지
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• 제20권3호
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• pp.371-380
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• 2004

In the dust separation by using porous filter media, the structure of dust layer deposited on the filter surface of filter medium directly affects the effective filtration. The present study has investigated the specific resistance (K$_2$') of the dust layer and its porosity ($\varepsilon$$_{c}$) for three different filters; FA composite filter, metal fiber filter and stainless filter. The specific resistance (K$_2$') increased and at the same time the cake porosity ($\varepsilon$$_{c}$) decreased with the increase of filtration velocity, possibly due to the compressible effect of dust layer. However, under the low dust concentration, subsequent dust particles would block the open channels through the layer resulting in high specific resistance of the layer. The FA composite filter among three filters was shown to be the most effective filter for dust cake filtration at low filtration velocities less than 0.1 m/s for an approximate dust concentration of 5 g/㎥.

• 한국음향학회:학술대회논문집
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• 한국음향학회 2004년도 추계학술발표대회논문집 제23권 2호
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• pp.183-186
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• 2004

Biot's theory and a modified Biot-Attenborough (MBA) model are applied to predict the dependences of acoustic characteristics on frequency and porosity in cancellous bone. The phase velocity and the attenuation coefficient predicted by both theories are compared with previous in vitro experimental measurements in terms of the mixed, the fast, and the slow waves. Biot's theory successfully predicts the dependences of phase velocity on frequency and porosity in cancellous bone, whereas a significant discrepancy is observed between predicted and measured attenuation coefficients. The MBA model is consistent with reported measurements for both dependences of phase velocity and attenuation coefficient on frequency and porosity. Based on the theoretical predictions from the MBA model, it is suggested that the attenuation coefficient of the mixed wave is dominated by the fast wave in the low-porosity region while it is dominated by the slow wave in the high-porosity region. This provides a qualitative explanation for the nonlinear relationship of attenuation of the mixed wave with porosity in cancellous bone.

• 한국세라믹학회지
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• 제52권6호
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• pp.467-472
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• 2015

The effect of $SrCO_3$ content on the microstructure, porosity, flexural strength, and pore size distribution of clay-based membrane supports was investigated. Green compacts prepared from low cost materials such as kaolin, bentonite, talc, sodium borate, and strontium carbonate were sintered at $1000^{\circ}C$ for 8 h in air. It was possible to control the porosity of the clay-based membrane supports within the range of 33% to 37% by adjusting the $SrCO_3$ content. The flexural strength of the clay-based membrane supports was found to strongly depend on their porosity. In turn, the porosity was affected by the $SrCO_3$ content. The average pore size and flexural strength of the clay-based membrane supports containing 4 wt% $SrCO_3$ were $0.62{\mu}m$ and 33 MPa at 34% porosity.

• 한국재료학회지
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• 제12권3호
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• pp.205-210
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• 2002

The HPS(High Porosity Support, 39.3%) and the LPS( Low Porosity Support, 18.7%) were fabricated to investigate the phase transformation and the chance of microstructure with porosity of alumina support. Alumina sol was made using aluminum tri-sec $butoxide(ATSB,\; Al(O-Bu)_3)$, the membrane on porous support with different porosity and the membrane without support were fabricated. The $\theta$-to ${\alpha}-A1_2O_3$ phase transformation in the membranes was investigated using thin film X-ray diffraction (XRD), and the change of microstructure was observed using scanning electron microscopy(SEM). XRD patterns showed that the membrane on LPS and HPS had 10$0^{\circ}C$, 5$0^{\circ}C$ higher $\theta$-to ${\alpha}-A1_2O_3$ transformation temperature compared to the unsupported membrane. A similar effect was also observed in microstructure of the membranes, theoritical temperature difference were 97$^{\circ}C$ and 44$^{\circ}C$ by Crapeyron equation.

• Advances in materials Research
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• 제6권4호
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• pp.329-341
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• 2017

The challenge of replacing conventional plastics with biodegradable composite materials has attracted much attention in product design, particularly in the tensile-related areas of application. In this study, fibres extracted from oil palm empty fruit bunch (EFB) were treated and utilized in reinforcing polyester matrix by hand lay-up technique. The effect of fibre loading and combined influence of alkali and silane treatments on porosity and water absorption parameters, and its correlation with the tensile behaviour of composites was analyzed. The results showed that tensile strength decreased whilst modulus of elasticity, water absorption and porosity parameters increased with increasing fibre loading. The composites of treated oil palm EFB fibre exhibited improved values of 2.47 MPa to 3.78 MPa for tensile strength; 1.75 MPa to 2.04 MPa for modulus of elasticity; 3.43% to 1.68% for porosity and 3.51% to 3.12% for water absorption at respective 10 wt.% fibre loadings. A correlation between porosity and water absorption with tensile behavior of composites of oil palm EFB fibre and positive effect of fibre treatment was established, which clearly demonstrate a connection between processing and physical properties with tensile behavior of fibre composites. Accordingly, a further exploitation of economic significance of oil palm EFB fibres composites in areas of low-to-medium tensile strength application is inferred.

• Steel and Composite Structures
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• 제49권3호
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• pp.281-291
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• 2023

Due to the fact that the nonlinear low-velocity impact response of graphene platelets reinforced metal foams (GPLRMF) doubly curved shells have not been investigated in the existing works, this paper aims to solve this issue. Using Reddy's high-order shear deformation theory (HSDT), the nonlinear governing equations of GPLRMF doubly curved shells are obtained by Euler-Lagrange method, discretized by Galerkin principle, and solved by the fourth-order Runge-Kutta method to obtain the impact force and central deflection. The nonlinear Hertz contact law is applied to determine the contact force. Finally, the impacts of graphene platelets (GPLs) distribution pattern, porosity distribution form, porosity coefficient, damping coefficient, impact parameters (radius and initial velocity), GPLs weight fraction, pre-stressing force and different shell types on the low-velocity impact curves are analyzed. It can be found that, among the four shell structures, the impact resistance of spherical shell is the best, while that of cylindrical shell is the worst.

• Journal of Advanced Marine Engineering and Technology
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• 제35권2호
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• pp.224-231
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• 2011

핀-휜 구조물이 삽입된 채널은 열전달이 향상되는 것으로 알려져 있다. 복잡한 핀-휜 구조물은 다공성 매체로 모사할 수 있을 만큼 매우 불규칙적인 유동을 보여준다. 본 연구는 수치해석을 통하여 핀-휜 구조물이 삽입된 채널의 열전달과 압력강하의 특성을 분석하였다. 유효유동공간비가 높고 직경이 큰 경우 실험데이터를 잘 예측 하였지만, 유효유동공간비가 낮은 경우 비교적 오차가 큰 편이었다. 유효유동 공간비가 낮을수록 유동교란이 강해져서 열전달이 증가하지만 압력강하도 증가하여 팬의 동력이 증가하기 때문에 최적점을 찾아서 설계하여야 한다. 본 연구에서는 전면유속이 5m/s 일 때, D25 모델에서는 유효유동공간비가 0.5인 지점에서, D05 모델에서는 0.9에서 압력강하가 급격하게 늘어나기 때문에 이보다 더 작은 유효유동공간비에서의 작동은 바람직하지 않다.

• 한국세라믹학회지
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• 제51권1호
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• pp.19-24
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• 2014

Three-layer porous alumina-mullite composites with a symmetric gradient porosity are prepared using a controlled freeze/gel-casting method. In this work, tertiary-butyl alcohol (TBA) and coal fly ash with an appropriate addition of $Al_2O_3$ were used as the freezing vehicle and the starting material, respectively. When sintered at $1300-1500^{\circ}C$, unidirectional macro-pore channels aligned regularly along the growth direction of solid TBA were developed. Simultaneously, the pore channels were surrounded by less porous structured walls. A high degree of solid loading resulted in low porosity and a small pore size, leading to higher compressive strength. The sintered porous layered composite exhibited improved compressive strength with a slight decrease in its porosity. After sintering at $1500^{\circ}C$, the layered composite consisting of outer layers with a 50 wt% solid loading showed the highest compressive strength ($90.8{\pm}3.7MPa$) with porosity of approximately 26.4%.