• Journal of the Korean Geotechnical Society
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• v.23 no.3
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• pp.77-88
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• 2007

A micromechanics-based model to simulate the elastic and elastic-plastic behavior of granular soils is developed. The model accounts for the fabric anisotropy represented by the statistical parameter of the spatial distribution of contact normals, the evolution of fabric anisotropy as a function of stress ratio, the continuous change of the co-ordination number relating to the void ratio, and the elastic and elastic-plastic microscopic contact stiffness. Using the experimental data for metallic materials, the elastic-plastic contact stiffness is derived as a power function of the normal contact force as well as the contact force initiating the yielding of contact bodies. To quantitatively assess microscopic model parameters, approximate solutions of cross-anisotropic elastic moduli are derived in terms of the micromechanical parameters.

• Korean Journal of Metals and Materials
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• v.48 no.9
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• pp.798-806
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• 2010

The effects of alloying elements and the cooling condition on the microstructure, tensile properties, and Charpy impact properties of high-strength bainitic steel plates fabricated by a controlled rolling process were investigated in the present study. Eight kinds of steel plates were fabricated by varying C, Cr, and Nb additions under two different cooling rates, and their microstructures and tensile and Charpy impact properties were evaluated. The microstructures present in the steels increased in the order of granular bainite, acicular ferrite, bainitic ferrite, and martensite as the carbon equivalent or cooling rate increased, which resulted in a decrease in the ductility and Charpy absorbed energy. The steels containing a considerable amount of bainitic ferrite or martensite showed very high strengths, together with good ductility and Charpy absorbed energy. In order to achieve the best combination of strength, ductility, and Charpy absorbed energy, granular bainite and acicular ferrite were properly included in the high-strength bainitic steels by controlling the carbon equivalent and cooling rate, while about 50 vol.% of bainitic ferrite or martensite was maintained to maintain the high strength.

• Korean Journal of Metals and Materials
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• v.50 no.7
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• pp.487-493
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• 2012

To analyze the factors on stretch-flangeability for 980 MPa-grade hot-rolled steels, two types of steels (Fe-Cr and Fe-Mo) were manufactured by hot-rolling. Manufactured steels at the low coiling temperature, such as 400 and $500^{\circ}C$, had poor stretch-flangeability due to un-uniformly distributed carbides and a large deviation of interphase hardness. However, when the coiling temperature was set at $650^{\circ}C$ with Fe-Cr steel, 998 MPa of ultimate tensile strength, 19% of total elongation and 65% of the hole expanding ratio were achieved by microstructural constituents of polygonal ferrite (PF) and granular ferrite (GF) dispersed with fine carbides (<50 nm). Therefore, the material to attain 980 MPa with superior formability was the Fe-Cr steel that was precipitation-hardened in polygonal ferrite and granular ferrite at the coiling temperature $650^{\circ}C$.

• Korean journal of applied entomology
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• v.32 no.1
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• pp.90-100
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• 1993

Ultrastructure of the larval hemocytes in Sericinus montela Grey was observed with the transmission and scanning electron microscope. The 5 cell types, according to Breh lin and Zachary(1986), identified in the hemocytes of the last instar S. montela larva were; prohemocyte, plasmatocyte, granular cell, spherule cell and oenocytoid. Prohemocytes could be easily charaterized by a relatively large nucleus nd poorly developed cytoplasmic organelles. Plasmatocytes were relatively large spindle-shaped or oval cells with fibrous bundles. The spindle-shaped plasmatocytes, especially, were characterized by a well developed, elongated nucleus. Granular cells had various granules, either morphologically or in electron density, and highly developed cytoplasmic organelles in the cytoplasm. They had numerous cytoplasmic processes. Spherule cells were characterized by cytoplasmic spherules containing fine materials, which are released into the hemolymph upon maturity of the cell. Oenocytoids consisted of electron dense materials and the organelles in cytoplasm were poorly developed.

• Journal of the Korean Geotechnical Society
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• v.25 no.8
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• pp.95-106
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• 2009

This study was intended to identify the effect of the wetting on a long-term compression settlement of the rock/soil mixture used as fill material, depending on compaction and grading conditions. The relatively large settlement happened under the fully-submerged condition, and a repeated settlement was monitored when moisture content increased over and over again like the rainfall infiltration. In case of the materials without fine fractions or compacted in wet condition, the settlement caused by wetting was relatively low. In conclusion, the long-term compression settlement of granular (rock/soil mixture) fill material is more affected by the increase of water content and temperature change (freezing and thawing) than creep.

• Korean Journal of Materials Research
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• v.8 no.6
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• pp.499-504
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• 1998

For the formation of cobalt polycide gate electrode, CoSi, was grown on columnar poly-Si, granular poly-Si or amorphous Si by depositing either Co monolayer or Co/Ti bilayer and its thermal stability was compared to study effects of the substrate crystallinity and the silicide formation method. When specimens were rapidly heat-treated at 90$0^{\circ}C$ up to 600 seconds, using amorphous Si or Co/Ti on all substrates improved the thermal stability. This was attributed to the uniform chemical composition of initial CoSi, and its smooth interface with the substrates, induced by smooth and clean Si surface and delayed Co diffusion. The main factors determining the thermal stability were found to be composition uniformity and smooth interface of $CoSi_2$, intially formed at the early stage of the heat-treatment.

• Electrical & Electronic Materials
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• v.16 no.1
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• pp.59.1-59
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• 2003

• Electrical & Electronic Materials
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• v.16 no.1
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• pp.60.1-60
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• 2003

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.70-70
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• 2007

• International Journal of Concrete Structures and Materials
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• v.3 no.1
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• pp.3-9
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• 2009

This paper examines the incorporation of the crushed sand (CS) and desert sand (DS) in the formation of self compacting concrete (SCC). These sands have been substituted for the rolled sand (RS), which is currently the only sand used in concretes and which is likely to run out in our country. DS, which comes from the Tunisian Sahara in the south, is characterized by a tight distribution of grains size. CS, a by-product of careers containing a significant amount of fines up to 15%, is characterized by a spread out granulometry having a maximum diameter of around 5mm. These two sands are considered as aggregates for the SCC. This first part of the study consists in analyzing the influence of the type of sand on the parameters of composition of the SCC. These sands consist of several combinations of 3 sands (DS, CS and RS). The method of formulation of the adopted SCC is based on the filling of the granular void by the paste. The CS substitution to the RS made it possible, for all the proportions, to decrease the granular voids, to increase the compactness of the mixture and to decrease the water and adding fillers proportioning. These results were also obtained for a moderate substitution of DS/CS (< 40%) and a weak ratio of DS/RS (20%). For higher proportions, the addition of DS to CS or RS did not improve the physical characteristics of the SCC granular mixture.