• The Journal of the Petrological Society of Korea
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• v.11 no.1
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• pp.30-48
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• 2002

Phenocrysts with rapakivi texture are easily observed in Bangeojin granite. The rapakivi texture is composed of inner pinkish alkali feldspars and white-colored mantling plagioclase. The Bangeojin granite distinctively includes lots of mafic microgranular enclaves and can be divided into five rock facies: (1) enclave-poor granite (EPG); (2) enclave-rich granite (ERG); (3) mafic microgranular enclave (MME); (4) hybrid zone between mafic microgranular enclave and granite (HZ); (5) hybrid zone-like enclaves (HLE). The rapakivi textures are observed in these five rock facies with no difference in shape and size. Plagioclase mantle commonly shows dendritic texture that is an important indicator to know the rapakivi genesis. The mantling texture would indicate supercooling condition during magma solidification process. In addition, mafic microgranular enclaves would imply the magma mingling environment. The magma mixing process had possibly caused the mantling texture. An abundance of rapakivi phenocrysts in HZ and the influxing phenomenon of the phenocrysts into MME support that there were physical chemical exchanges during the mingling. And this model of the magma mixing/mingling explain well the heterogeneous distribution of the rapakivi phenocrysts in the five rock facies. Therefore the rapakivi textures in the Bangeojin granite would have been formed by magma mixing process.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.3
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• pp.199-206
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• 2014

In this paper, a scheme to evaluate the response variability for functionally graded material (FGM) beam with varying sectional area is presented. The randomness is assumed to appear in a spatial domain along the beam axis in the elastic modulus. The functionally graded material categorized as composite materials, however without the drawbacks of delamination and occurrence of cracks due to abrupt change in material properties between layers in the conventional composite materials. The functionally graded material is produced by the gradual solidification through thickness direction, which endows continuous variation of material properties, which makes this material performs in a smooth way. However, due to difficulties in tailoring the gradients, to have uncertainty in material properties is unavoidable. The elastic modulus at the center section is assumed to be random in the spatial domain along the beam axis. Introducing random variables, defined in terms of stochastic integration, the first and second moments of responses are evaluated. The proposed scheme is verified by using the Monte Carlo simulation based on the random samples generated employing the spectral representation scheme. The response variability as a function of correlation distance, the effects of material and geometrical parameters on the response variability are investigated in detail. The efficiency of the proposed scheme is also addressed by comparing the analysis time of the proposed scheme and MCS.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.9
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• pp.1438-1443
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• 2001

The significance of the casting/forging process for reducing the production cost of large components is being noted in these days. This casting/forging process is a method of forging a workpiece preformed by casting into the final shape. In this study, the casting/forging process has been applied in manufacturing a large aluminum flange in order to reduce press capacity and material cost. Firstly, a hot compression test was performed with cast cylindrical billets in order to determine the optimum forging condition of the aluminum flange. The optimum range of forging temperature of Al 5083 was from 420$\^{C}$ to 450$\^{C}$. The suitable strain rate was 1.5 sec(sup)-1. The deformation amount of a preform of a preform in a forging process is a key role in the mechanical properties of casting/forging products. In order to find the change of mechanical properties according to effective stain of cast aluminum billets, a hot upsetting test were performed with rectangular blocks and then a uniaxial tensile test was performed with specimens cut from the upsetted billets. The tensile strength and the elongation of cast/upsetted aluminum billets were increased largely until the effective strain was 0.7. FE analysis was performed to determine the configurations of case preform and die for an aluminum flange. In the FE analysis, the forging load-limit was fixed 1500ton for low equipment cost. The cast preform was designed so that the effective stain around the neck of a flange exceeded 0.7. From the result of FE analysis, optimal configurations of the cast preform and the die were designed for a large flange. The filling and solidification analysis for a sound cast-preform was carried out with MAGMA soft. In the forging experiment for an aluminum flange, it was confirmed that the optimal configuration of the cast preform predicted by FE analysis was very useful. The cast/forged products using designed preform were made perfectly without any defects.

• Journal of Conservation Science
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• v.32 no.4
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• pp.549-560
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• 2016

The purpose of this study is to identify the material characteristics of blackwares excavated from the Bonggok kiln site in Jinan-gun, Jeollabuk-do Province, South Korea, by scientific analyses and a reproduction experiment. Scientific analyses were conducted to determine the physical properties, chemical composition and for microscopic observation of blackwares. A reproduction experiment was also conducted by producing ceramic samples with black glaze, red ocher and limestone, and then cross sections of the samples were observed. The analysis results showed that all the excavated blackwares have similar properties such as chromaticity, specific gravity, absorption factor and porosity, but there is a difference depending on the crystallization of the ceramics. Thermal analysis showed that the exothermic peak was observed at about $1200^{\circ}C$, and crystal structure analysis indicated the presence of mullite. Hence, it can be concluded that the firing temperature of the excavated blackwares was around $1100-1200^{\circ}C$. Moreover, the glaze present on these blackwares has about 22% higher $Fe_2O_3$ content than those excavated from other places; however, the former has lower CaO content. For the reproduction experiment, samples were made using limestone as a flux and red ocher as a glaze. The results show that the cross section of the glaze layer of the reproduced sample have iron crystals with dendritic structures, similar to those present in the excavated black-wares. It is assumed that such iron crystals were formed during the process of melting and solidification of the iron oxide present in the blackwares.

• Journal of Korea Foundry Society
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• v.35 no.6
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• pp.147-154
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• 2015

The effects of Sc and Sr elements on the modification of the eutectic $Mg_2Si$ phase and the castability were investigated in the Al-4wt%Mg-0.9wt%Si-0.3wt%Mn-0.15wt%Fe alloy. Measurements of the cooling curve and microstructure observations were performed to analyze the additional effects of Sc and Sr minor elements during the solidification process. A prominent effect found on the modification of the eutectic $Mg_2Si$ phase with additions of the Sr and Sc elements. Here, a fine eutectic $Mg_2Si$ phase and a decrease in the growth temperature of the eutectic $Mg_2Si$ phase were evident with an addition of Sc element up to 0.2 wt%. The growth temperature of the eutectic $Mg_2Si$ phase decreased and the effect on the modification of the eutectic $Mg_2Si$ phase increased with the addition of Sr element up to 0.02 wt%. The addition of 0.02wt%Sr had the strongest effect on the modification of the eutectic $Mg_2Si$ phase, and the resulting microstructure of the eutectic $Mg_2Si$ phase was found to have a fibrous morphology with a decreased aspect ratio and an increased modification ratio. Fluidity and shrinkage tests were conducted to evaluate the castability of the alloy. The addition of 0.02wt%Sr effectively increased the fluidity of the alloy, while an addition of Sc did not show any effect compared to when nothing was added. The maximum filling length was recorded for 0.01wt%TiB-0.02wt%Sr owing to the effect of the fine ${\alpha}$-Al grains. The macro-shrinkage ratio decreased, while the micro-shrinkage ratio increased with the addition of various eutectic modifiers. The highest ratio of micro-shrinkage was recorded for the 0.02wt%Sr condition. However, the total shrinkage ratio was nearly identical regardless of the amounts added in this study.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.277-282
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• 2015

This study is conducted to utilize waste concrete powder (WCP) made as a by-product manufacturing high quality recycled aggregate. The blaine fineness of the used waste concrete powder was $928cm^2/g$. As the main characteristic of waste concrete powder, it showed an angular type similar to cement, but hydrated products were attached on the surface of particles. In addition, the size of the particles of waste concrete powder was larger than OPC and in terms of chemical components it had higher $SiO_2$ contents. For using WCP in soil cement-based pavement, the qualities, physical and chemical properties, of WCP should be researched. In the first step, the specified compressive strength of mortar for two types of clay sand soil and clay soil respectively was experimented to be 15 MPa and then optimum mixing ratio of chemical solidification agent were decided in the range of 1.5 - 3.0% in the replacement with cement weight content. In the second step, based on the prior experimental results, recycling possibility of WCP in soil cement-based pavement was studied. In the result of experiment the mixing ratio of WCP were 5, 10, 15 and 20% in the replacement with soil weight and the compressive strength of mortar was somewhat decreased according to the increase of the mixing ratio of WCP.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.5
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• pp.345-349
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• 2000

$Al_2O_3/ZrO_2$eutectic fibers were grown by micro-pulling down technique and investigated their microstructure as a function of solidification rate. $Al_2O_3/ZrO_2$eutectic fibers 0.2~2 mm in diameter and 500 mm in length have been grown with a pulling rate of 0.1~15 mm/min. The eutectic microstructures changed as a function of fulling rate from rod-shaped to cellular shape containing some thin lamellar pattern via uniform lamellar structure. Typical lamellar thickness decreased from about 380 nm to 110 nm as the pulling rate increased from 1 mm/min to 15 mm/min. The interlamellar spacing fitted with the inverse-square-root dependence on pulling rate according to $\lambda$= $1{\times}v^{-1/2}$, where $\lambda$ has the dimension in $\mu\textrm{m}$ and v is $\mu\textrm{m}$/s. Hardness value reached 13.1 GPa at 15 mm/min of pulling rate and tensile strength 900 MPa at 10 mm/min were also increased as the interlamellar spacing decreased.

• Journal of The Korean Association For Science Education
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• v.22 no.2
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• pp.215-229
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• 2002

This study is to analyze the contents related to 'state of water', 'state change of water', and 'conditions of state change' in K-12 science textbooks. For this, we analyzed textbooks based on the 5th kindergarten curriculum, the 6th elementary school science curriculum and the 6th middle school science curriculum. Findings show that some of the contents are designed well by topical sequencing or by spiral sequencing. But others have some problems based on topical sequencing and spiral sequencing. Generally, the contents are represented in the order of Perception of phenomena with senses level, Macroscopic understanding level, Understanding of scientific term level, Microscopic understanding level by grade. But the state change contents related to solidification and melting, and conditions of state change contents related to heat, temperature, wind, and humidity are not represented in the level of Microscopic understanding. The contents of state change and conditions related to heat and wind are not represented in the level of scientific term also.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.9 no.2
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• pp.81-86
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• 2011

Polymer-modified cement is the composite material made by partially replacing and strengthening the cement hydrate binders of conventional mortar with polymeric modifiers such as polymer latexes and redispersible polymeric modifiers. It is known that the addition of polymer to cement mortar leads to improved quality, which would be expected to have a high chemical resistance. Therefore, the purpose of this study is to identify the improved chemical resistance, such as low permeability and low ion diffusivity, of the polymer-modified cement as a solidification agent for the radwaste. First, polymer-modified cement specimens by latex modification were prepared according to the polymer content from 0% to 30% to select the optimized polymer content. At those specimens, the water-to-cement (W/C) ratio was maintained to 33% and 50% respectively. After the much curing time, the structural integrity of specimens was evaluated through the compressive strength test and the porosity evaluation by the water immersion method. From the results, 10% of the polymer content at 33% of the W/C ratio was shown to have the most improved quality. Finally, the leaching test referredfrom ANS 16.1 for the specimens having the most improved quality was conducted. Dedicated specimens for the leaching test were then mixed with radioisotopes of $^{60}Co$ and $^{137}Cs$ at the specimen preparation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.2
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• pp.113-119
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• 2006

Brazing is an important manufacturing process in the fabrication of Heavy Water Reactor fuel rods, in which bearing and spacer pads are joined to Zircaloy-4 cladding tubes. The physical vapor deposition(PVD) technique is currently used to deposit metallic Be on the surfaces of pads as a filler metal. Amorphous Zr-Be binary alloys which are manufactured by rapid solidification process are under developing to substitute the conventional PVD-Be coating. In the present study, brazed joint with PVD and amorphous alloys of $Zr_{1-x}Be_{x}(0.3{\le}x{\le}0.5)$ as filler metals are compared by mechanism, microstructure and hardness. The thickness of brazed joint with amorphous alloys became much smaller than that of PVD-Be. The erosion of base metal did not occur in the brazed joint with amorphous alloys. The brazing mechanism for PVD-Be seems to be Be diffusion into Zr-4 with capillary action resulting from eutectic reaction while that for amorphous alloys are associated with the liquid phase formation in the brazed joint. The brazed joint microstructure with PVD-Be consists of dendrite while that with amorphous alloys is globular. The $Zr_{0.7}Be_{0.3}$ alloy shows the smooth interface with little erosion in the base metal and is recommended a most suitable brazing filler metal for Zircaloy-4.