• Title, Summary, Keyword: Volume Fraction

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A Study on Mold Filling and Fluidity of Mg Alloy in Thixocasting (Mg합금의 반용융가압주조시 주조조건에 의한 금형충전성 및 유동성 변화)

  • Jung, Woon-Jae;Kim, Ki-Tae;Hong, Chun- Pyo
    • Journal of Korea Foundry Society
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    • v.15 no.2
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    • pp.184-193
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    • 1995
  • Effects of process parameters during thixocasting, such as solid volume fraction, mold temperature and extrusion ratio, on the mold filling behaviour and fluidity of Mg alloy(AZ91D) have been investigated. The semi-solid ingot held for 60 minutes at the semi-solid temperature range did not contain the equilibrium volume fraction of solid as expected from the phase diagram. Therefore, in order to obtain the desired solid fractions, and to suppress the exaggerated grain growth during heating, it was required to heat the ingot rapidly up to the temperature $10^{\circ}C$ higher than the semi-solid temperature suggested from the phase diagram for a specific volume fraction of solid. The experimental results show that mold filling behaviour and fluidity can be improved with the use of the higher mold temperature and the lower volume fraction of solid, but remain nearly unaffected by the change of extrusion ratio.

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Tensile Properties of GFRP Rebars Based on Resin Mix Proportions (수지배합에 따른 GFRP 보강근의 인장 특성)

  • Park, Ji-Sun;You, Young-Chan;Park, Young-Hwan;You, Young-Jun;Kim, Hyeong-Yeol;Kim, Keung-Hwan
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.561-564
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    • 2006
  • The tensile characteristics of four types GFRP (glass fiber reinforced polymer) reinforcing bars with different resin mix proportions and fiber volume fraction were analyzed experimentally. Four types of GFRP reinforcing bars containing approximately 66 or 70% fiber volume fraction with A or B rein mix proportions were considered in this test. All testing procedures including specimens preparation, set-up of test equipments and measuring devices were made according to the recommendations of CSA Standard S806-02. From the test results, it was found that GFRP reinforcing bars containing approximately 70% fiber volume fraction with A rein mix proportion showed the higher tensile strength than that of the others due to the higher fiber volume fraction and proper resin mix proportion.

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Experimental Study on Characteristics of Synergistic Effect of Fuel Mixing on Number Density and Size of Soot in Ethylene-base Counterflow Diffusion Flames by Laser Techniques

  • Choi, Jae-Hyuk
    • Journal of the Korean Society of Marine Engineering
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    • v.33 no.3
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    • pp.378-386
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    • 2009
  • The effect of fuel mixing on soot structure with methane, ethane, and propane to ethylene-base counterflow diffusion flames has been investigated by measuring the volume fraction, number density, and particle size of soot by adopting the light extinction/scattering techniques. The experimental result showed that the mixing of ethane and propane in ethylene diffusion flame increased soot volume fraction while the mixing of methane decreased. As compare to the ethylene-base flame, the diameters of soot particles for mixture flames are slightly smaller. While the soot number densities for the mixture flames are much higher. Thus, the increase in the soot volume fraction can be attributed to the appreciably increased soot number density by the fuel mixing.

Pore Filling Theory of Liquid Phase Sintering and Microstrcture Evolution (액상소결의 기공채움 이론과 미세구조 발달)

  • 이성민
    • Journal of Korean Powder Metallurgy Institute
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    • v.6 no.1
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    • pp.81-87
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    • 1999
  • Based on the pore filling theory, the microstructure evolution during liquid-phase sintering has been analyzed in terms of interrelationship between average grain size and relative density. For constant liquid volume fraction, the microsturucture trajectories reduced to a single curve in a grain size(x)-density(y) map, regardless of grain growth constant. The slope of curves in the map was inversely proportional to average pore size, while it increased fapidly with liquid volume fraction. Increase in pore volume fraction retarded the densification considerably, but showed marginal effect on the slope. The activation energy of densification was predicted to be the same as that of grain growth as long as the liquid volume fraction is constant for any temperature range studied. The present analyses on microstricture evolution may demonstrate the usefulness of pore filling theory and provide a guideline for process optimization of liquid-phase sintering.

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Prediction of Distribution of Solid Volume Fraction in Semi-Solid Materials Based on Mixture Theory (혼합이론에 근거한 반용융 재료의 고상률 분포 예측)

  • 윤종훈;김낙수;임용택
    • Transactions of Materials Processing
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    • v.8 no.4
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    • pp.399-406
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    • 1999
  • It is more appropriate to treat that the semi-solid mixture as a single phase material that obeys incompressibility in the global sense and to analyze the liquid flow only locally than the approach based on compressible yield criteria. In the present study, a numerical algorithm of updating the solid volume fraction based on mixture theory has been developed. Finite element analysis of simple upsetting was carried out using the proposed algorithm to investigate the degree of macro-segregation according to friction conditions and compressive strain rates under the isothermal condition. The simulation results were compared to experimental results available in reference to test the validity of the currently proposed algorithm. Since the comparison results show a good agreement it is construed that the proposed algorithm can contribute to the development of numerical analysis of determining the solid volume fraction semi-solid processing.

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Viscoelastic behavior on composite beam using nonlinear creep model

  • Jung, Sung-Yeop;Kim, Nam-Il;Shin, Dong Ku
    • Steel and Composite Structures
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    • v.7 no.5
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    • pp.355-376
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    • 2007
  • The purpose of this study is to predict and investigate the time-dependent creep behavior of composite materials. For this, firstly the evaluation method for the modulus of elasticity of whole fiber and matrix is presented from the limited information on fiber volume fraction using the singular value decomposition method. Then, the effects of fiber volume fraction on modulus of elasticity of GFRP are verified. Also, as a creep model, the nonlinear curve fitting method based on the Marquardt algorithm is proposed. Using the existing Findley's power creep model and the proposed creep model, the effect of fiber volume fraction on the nonlinear creep behavior of composite materials is verified. Then, for the time-dependent analysis of a composite material subjected to uniaxial tension and simple shear loadings, a user-provided subroutine UMAT is developed to run within ABAQUS. Finally, the creep behavior of center loaded beam structure is investigated using the Hermitian beam elements with shear deformation effect and with time-dependent elastic and shear moduli.

Numerical investigation on tortuosity of transport paths in cement-based materials

  • Zuo, Xiao-Bao;Sun, Wei;Liu, Zhi-Yong;Tang, Yu-Juan
    • Computers and Concrete
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    • v.13 no.3
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    • pp.309-323
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    • 2014
  • Based on the compositions and structures of cement-based materials, the geometrical models of the tortuosity of transport paths in hardened cement pastes, mortar and concrete, which are associated with the capillary porosity, cement hydration degree, mixture particle shape, aggregate volume fraction and water-cement ratio, are established by using a geometric approach. Numerical simulations are carried out to investigate the effects of material parameters such as water-cement ratio, volume fraction of the mixtures, shape and size of aggregates and cement hydration degree, on the tortuosity of transport paths in hardened cement pastes, mortar and concrete. Results indicate that the transport tortuosity in cement-based materials decreases with the increasing of water-cement ratio, and increases with the cement hydration degree, the volume fraction of cement and aggregate, the shape factor and diameter of aggregates, and the material parameters related to cement pastes, such as the water-cement ratio, cement hydration degree and cement volume fraction, are the primary factors that influence the transport tortuosity of cement-based materials.

Material distribution optimization of 2D heterogeneous cylinder under thermo-mechanical loading

  • Asgari, Masoud
    • Structural Engineering and Mechanics
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    • v.53 no.4
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    • pp.703-723
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    • 2015
  • In this paper optimization of volume fraction distribution in a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) and subjected to steady state thermal and mechanical loadings is considered. The finite element method with graded material properties within each element (graded finite elements) is used to model the structure. Volume fractions of constituent materials on a finite number of design points are taken as design variables and the volume fractions at any arbitrary point in the cylinder are obtained via cubic spline interpolation functions. The objective function selected as having the normalized effective stress equal to one at all points that leads to a uniform stress distribution in the structure. Genetic Algorithm jointed with interior penalty-function method for implementing constraints is effectively employed to find the global solution of the optimization problem. Obtained results indicates that by using the uniform distribution of normalized effective stress as objective function, considerably more efficient usage of materials can be achieved compared with the power law volume fraction distribution. Also considering uniform distribution of safety factor as design criteria instead of minimizing peak effective stress affects remarkably the optimum volume fractions.

Effect of Filament Winding Methods on Surface Roughness and Fiber Volume Fraction of SiCf/SiC Composite Tubes (SiCf/SiC 복합체 튜브의 표면조도 및 섬유 부피 분율에 미치는 필라멘트 와인딩 방법의 영향)

  • Kim, Daejong;Lee, Jongmin;Park, Ji Yeon;Kim, Weon-Ju
    • Journal of the Korean Ceramic Society
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    • v.50 no.6
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    • pp.359-363
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    • 2013
  • Silicon carbide and its composites are being considered as a nuclear fuel cladding material for LWR nuclear reactors because they have a low neutron absorption cross section, low hydrogen production under accident conditions, and high strength at high temperatures. The SiC composite cladding tube considered in this study consists of three layers, monolith CVD SiC - $SiC_f$/SiC composite -monolith CVD SiC. The volume fraction of SiC fiber and surface roughness of the composite layer affect mechanical and corrosion properties of the cladding tube. In this study, various types of SiC fiber preforms with tubular shapes were fabricated by a filament winding method using two types of Tyranno SA3 grade SiC fibers with 800 filaments/yarn and 1600 filaments/yarn. After chemical vapor infiltration of the SiC matrix, the surface roughness and fiber volume fraction were measured. As filament counts were changed from 800 to 1600, the surface roughness increased but the fiber volume fraction decreased. The $SiC_f$/SiC composite with a bamboo-like winding pattern has a smaller surface roughness and a higher fiber volume fraction than that with a zigzag winding pattern.

Flexural Performance Characteristics of High Performance Slurry Infiltrated Fiber Reinforced Cementitious Composite according to Fiber Volume Fraction (섬유혼입률에 따른 고성능 슬러리 충전 강섬유보강 시멘트 복합체의 휨성능 특성)

  • Kim, Seung-Won;Cho, Hyun-Myung;Lee, Hak-Yong;Park, Cheol-Woo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.19 no.4
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    • pp.109-115
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    • 2015
  • High performance fiber reinforced cementitious composite (HPFRCC) can provide high fracture energy absorption as well as high strength with high fiber volume fraction. The increased fracture energy helps resisting high frequency loadings, such as earthquake, impact or blast. This study investigates the flexural performance of slurry infiltrated fiber concrete (SIFCON), one of the important HPFRCC, with respect to varying fiber volume fraction. The maximum fiber volume fraction was 8.0 % and reduced to 6.0% by 0.5% and the maximum volume fraction is obtained by packing fibers with simple tapping by hands. The used fiber was a steel fiber with the length 30 mm and the diameter of 0.5 mm. The flexural strengths were 48.7 MPa at 8.0 % and 22.8 MPa at 6.0 %. The measured flexural strength is much higher compared to other cememtitious composite materials but decreased proportional to the fractions. This result implies that for SIFCON considered herein the reduced amount of steel fibers may affect its flexural performance in a negatively way. The flexural toughness, an index to represent the fracture energy absorption, also decreased with the reduced fiber amount.