• Title/Summary/Keyword: Shape Aspect Ratio

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A 2-D numerical research on spatial variability of concrete carbonation depth at meso-scale

  • Pan, Zichao;Ruan, Xin;Chen, Airong
    • Computers and Concrete
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    • v.15 no.2
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    • pp.231-257
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    • 2015
  • This paper discusses the spatial variability of the carbonation depth caused by the mesoscopic structure of the concrete and the influence of the spatial variability on the thickness of the concrete cover. To conduct the research, a method to generate the random aggregate structure (RAS) based on polygonal particles and a simplified numerical model of the concrete carbonation at meso-scale are firstly developed. Based on the method and model, the effect of the aggregate properties including shape, content and gradation on the spatial variability of the carbonation depth is comprehensively studied. The results show that a larger degree of the spatial variability will be obtained by using (1) the aggregates with a larger aspect ratio; (2) a larger aggregate content; (3) the gradation which has more large particles. The proper sample size and model size used in the analysis are also studied. Finally, a case study is conducted to demonstrate the influence of the spatial variability of the carbonation depth on the proper thickness of the concrete cover. The research in this paper not only provides suggestions on how to decrease the spatial variability, but also proposes the method to consider the effect of the spatial variability in designing the thickness of the concrete cover.

Thermal Conductivity and Adhesion Properties of Thermally Conductive Pressure-Sensitive Adhesives

  • Kim, Jin-Kon;Kim, Jong-Won;Kim, Myung-Im;Song, Min-Seok
    • Macromolecular Research
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    • v.14 no.5
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    • pp.517-523
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    • 2006
  • The effects of particle content, size and shape on the thermal conductivity (k) and adhesion properties of thermally conductive, pressure-sensitive adhesives (PSAs) were investigated. The matrix resins were thermally crosslinkable, 2-ethylhexyl acrylic polyol and ultraviolet (UV)-curable, random copolymer consisting of acrylic oligomer and various acrylates. We found that k increased with increasing diameter and particle aspect ratio, and was further enhanced due to the reduction of the interfacial thermal barrier when the coupling agent, which increases the adhesion between particles and the matrix resin, was used. On the other hand, adhesion properties such as peel strength and tack of the thermally crosslinkable resin decreased sharply with increasing particle content. However, for UV curable resin, increased particle addition inhibited the decrease in adhesion properties.

Milling and Particulate Characteristics of Al Alloy-Al2O3 Powder Mixtures for Reaction-Bonded Al2O3(RBAO) Process

  • Lee, Hyun-Kwuon
    • Korean Journal of Materials Research
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    • v.23 no.10
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    • pp.574-579
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    • 2013
  • The milling and particulate characteristics of Al alloy-$Al_2O_3$ powder mixtures for a reaction-bonded $Al_2O_3$ (RBAO) process were studied. A commercially available prealloyed Al powder with Zn, Mg, Cu and Cr alloying elements (7475 series) was mixed with a calcined sinter-active $Al_2O_3$ powder and then milled in centrifugal milling equipment for ~48 hrs. The Al alloy-$Al_2O_3$ powder mixtures after milling were characterized and evaluated in various ways to reveal their particulate characteristics during milling. The milling efficiency of the Al alloy increased with a longer milling time. Comminution of the Al alloy particles started with its elongation, showing a high aspect ratio. With a longer milling time, the elongated Al alloy particle changed in terms of its shape and size, becoming equiaxially fine particles. Regardless of the milling efficiency of the Al alloy particles, all of the Al alloy particles repeatedly experienced strong plastic deformation during milling, giving rise to higher density of surface defects, such as microcracks, and leading to higher residual microstress within the Al alloy particles. The chemical reactions, oxidation behavior and hydration behavior of the Al alloy particles and the hydrolysis characteristics of their reaction with the environment were also observed during the milling process and during the subsequent powder handling steps.

Magnetic Properties of Ni Nanostructures Made by using Nanoporous Anodic Alumina (AAO를 이용한 Ni 나노구조체의 자기적 특징)

  • Lee, S.G.;Shin, S.W.;Lee, J.;Lee, J.H.;Kim, T.G.;Song, J.H.
    • Journal of the Korean Magnetics Society
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    • v.14 no.3
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    • pp.105-108
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    • 2004
  • Array of magnetic Ni nanostructures has been fabricated on Si substrate by using nanoporous alumina film as a mask during deposition. The nanostructures are truncated cone-shape and the lateral sizes are comparable to height. While the continuous film shows well-defined in-plane magnetization, the nanostructure shows perpendicular component of magnetization at remanence. The hysterectic behavior of nanostructures is dominated by the demagnetizing field instead of interaction among them.

Fabrication of a Micro Die by LIGA Process and Hybrid Powder Extrusion Process of Micro-spur Gear (LIGA 공정을 이용한 초소형 스퍼기어 금형 제작 및 하이브리드 분말 압출성형)

  • Lee, K.H.;Hwang, D.W.;Kim, J.H.;Jang, S.S.;Kim, B.M.
    • Transactions of Materials Processing
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    • v.19 no.6
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    • pp.352-356
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    • 2010
  • This paper was designed to fabricate the micro-spur gear by the LIGA and hybrid powder extrusion process. It is important to manufacture a micro-die with a high aspect ratio and determine appropriate extrusion conditions for a microforming. Ni has been used to fabricate micro-dies. LIGA process was capable to produce micro-extrusion dies with close tolerance, longer bearing length and adequate surface quality. Superplastic Al-78Zn powders have the great advantage in achieving deformation under low stresses and exhibiting good micro-formability with average strain rate raging from $10^{-3}$ to $10^{-2} s^{-1}$ and constant temperature ranging from 503 to 563K. Al-78Zn powders were compacted into a cylindrical shape ($\Phi3\times$h10mm) under compressive force of 10kN and, subsequently, the compacted powders were extruded by the hybrid powder extrusion process controlling of the temperature holing time for a improvement on formability of Al-22Zn powder. Micro-extrusion has succeeded in forming micro-gear shafts.

Study on Fabrication of Highly Ordered Nano Master by Using Anodic Aluminum Oxidation (AAO를 이용한 나노 마스터 제작에 관한 연구)

  • Kwon, J.T.;Shin, H.G.;Seo, Y.H.;Kim, B.H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2007.10a
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    • pp.162-165
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    • 2007
  • AAO(Anodic Aluminum Oxidation) method has been known that it is practically useful for the fabrication of nano-structures and makes it possible to fabricate the highly ordered nano masters on large surface and even on the 2.5 or 3D surface at low cost comparing to the expensive e-beam lithography or the conventional silicon processing. In this study, by using the multi-step anodizing and etching processes, highly ordered nano patterned master with concave shapes was fabricated. By varying the processing parameters, such as initial matter and chemical conditions; electrical and thermal conditions; time scheduling; and so on, the size and the pitch of the nano pattern can be controlled. Consequently, various alumina/aluminum nano structures can be easily available in any size and shape by optimized anodic oxidation in various aqueous acids. In order to replicate nano patterned master, the resulting good filled uniform nano molded structure through electro-forming process shows the validity of the fabricated nano pattern masters.

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Effects of Reynolds Number on Flow and Heat/Mass Characteristics Inside the Wavy Duct (Reynolds 수에 따른 꺾어진 덕트에서 열/물질전달 특성 고찰)

  • 장인혁;황상동;조형희
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.10
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    • pp.809-820
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    • 2003
  • The present study investigates effects of flow velocity on the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewall are determined by using a naphthalene sublimation technique. The flow visualization technique is used to understand the overall flow structures inside the duct. The aspect ratio and corrugation angle of the wavy duct is fixed at 7.3 and 145$^{\circ}$ respectively, and the Reynolds numbers, based on the duct hydraulic diameter, vary from 100 to 5,000. The results show that there exist complex secondary flows and transfer processes resulting in non-uniform distributions of the heat/mass transfer coefficients on the duct side walls. At low Re (Re<1000), relatively high heat/mass transfer regions like cell shape appear on both pressure and suction side wall due to the secondary vortex flows called Taylor-Gortler vortices perpendicular to the main flow direction. However, at high Re (Re>1000), these secondary flow cells disappear and boundary layer type flow characteristics are observed on pressure side wall and high heat/mass transfer region by the flow reattachment appears on the suction side wall. The average heat/mass transfer coefficients are higher than those of the smooth circular duct due to the secondary flows inside wavy duct. And also friction factors are about two times greater than those of the smooth circular duct.

Study of Welding Characteristics of Inconel 600 Alloy using a Continuous Wave Nd:YAG Laser Beam (연속파형 Nd:YAG 레이저를 이용한 인코넬 600 합금의 맞대기 용접 특성 연구)

  • Song, Seong-Wook;Yoo, Young-Tae;Shin, Ho-Jun
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1154-1159
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    • 2004
  • Laser beam welding is increasingly being used in welding of structural steels. The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and deep penetration. The thermal cycles associated with laser welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone. Experiments are performed for Inconel 600 plates changing several process parameter such as laser power, welding speed, shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between plate and plate, etc. The follow conclusions can be drawn that laser power and welding speed have a pronounced effect on size and shape of the fusion zone. Increase in welding speed resulted in an increase in weld depth/ aspect ratio and hence a decrease in the fusion zone size. The penetration depth increased with the increase in laser power . Welding characteristics of austienite Inconel 600 using a continuous wave Nd:YAG laser are experimentally investigated. This paper describes the weld ability of inconel 600 for machine structural use by Nd:YAG laser.

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Effect of Hot Isostatic Pressing on Elimination of Internal Defects in IN738LC Superalloy for Gas Turbine Blade (HIP 처리에 의한 가스터빈 블레이드용 IN738LC 초합금의 내부결함 소멸 효과)

  • Park, Young-Kyu;Kim, Soo-Hyung;Kim, Jae-Cheol;Lee, Young-Chan;Kim, Doo-Soo;Choi, Cheol;Kim, Gil-Moo
    • Journal of Korea Foundry Society
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    • v.19 no.5
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    • pp.427-432
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    • 1999
  • Most investment castings contain some porosities and microcavities. In this study, we investigated the elimination trends of various internal defects in IN738LC investment castings for industrial gas turbine blade by hot isostatic pressing. The results showed that cylindrical defects which are under $0.6mm{\Phi}{\times}7mm$ size are mostly eliminated and aspect ratio of defects is more sensitive factor than their cross section shape in removing these defects. Increasing hot isostatic pressure and holding time doesn't affect the elimination trend of cylindrical defects over $0.6mm{\Phi}{\times}7mm$ size because first step(plastic deformation) of HIP densification doesn't occur under these HIPping conditions.

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Numerical simulation of hot embossing filling (핫엠보싱 충전공정에 관한 수치해석)

  • Kang T. G.;Kwon T. H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2005.05a
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    • pp.43-46
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    • 2005
  • Micro molding technology is a promising mass production technology for polymer based microstructures. Mass production technologies such as the micro injection/compression molding, hot embossing, and micro reaction molding are already in use. In the present study, we have developed a numerical analysis system to simulate three-dimensional non-isothermal cavity filling for hot embossing, with a special emphasis on the free surface capturing. Precise free surface capturing has been successfully accomplished with the level set method, which is solved by means of the Runge-Kutta discontinuous Galerkin (RKDG) method. The RKDG method turns out to be excellent from the viewpoint of both numerical stability and accuracy of volume conservation. The Stokes equations are solved by the stabilized finite element method using the equal order tri-linear interpolation function. To prevent possible numerical oscillation in temperature Held we employ the streamline upwind Petrov-Galerkin (SUPG) method. With the developed code we investigated the detailed change of free surface shape in time during the mold filling. In the filling simulation of a simple rectangular cavity with repeating protruded parts, we find out that filling patterns are significantly influenced by the geometric characteristics such as the thickness of base plate and the aspect ratio and pitch of repeating microstructures. The numerical analysis system enables us to understand the basic flow and material deformation taking place during the cavity filling stage in microstructure fabrications.

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