• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.5
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• pp.618-622
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• 2011

Specialized large-scale computational finite-element and molecular dynamic models have been used in order to understand and predict how dislocation density emission and contact stress field due to nanoindentation affect inelastic deformation evolution scales that span the molecular to the continuum level in ductile crystalline systems. Dislocation density distributions and local stress fields have been obtained for different crystalline slip-system and grain-boundary orientations. The interrelated effects of grain-boundary interfaces and orientations, dislocation density evolution and crystalline structure on indentation inelastic regions have been investigated.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.68 no.1
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• pp.1-7
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• 2023

We studied the changes in growth characteristics of major cultivated rice in low- density transplanting. The culm and spikelet length did not change in low density transplanting conditions. As the distance between hills increased by 10 cm, the number of tillers per hill increased by an average of 4.4 and the number of grains per spikelet increased by 7.5. The cultivar that had more tillers and higher grain number in 80 hills per 3.3 m² tended to have more tillers and grain in low-density transplanting conditions. However, the increase rate of tillers and grain in low-density transplanting was not significanty different from the tiller and grain number in 80 hills per 3.3 m². The total branch number and branch length in spikelets increased in low-density transplanting conditions. The grain number per spikelet was also increased by the in low-density transplanting method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.05a
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• pp.149-151
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• 2006

The surface properties of electrical devices studied by fractal phenomenon were investigated. The SEM photographs of devices surface were changed by binary code and it were analyzed by fractal dimension. The void of devices surface was found by fractal program. The relation between grain density and electrical properties are able to expect to fractal dimension. The grain size in varistors surface was decreased by increasing of oxide antimony addition. The fractal dimension and electrical properties of devices surface was related to between grain boundary and grain density. The grain size was decreased by increasing of fractal dimensions.

• Journal of the Korean Ceramic Society
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• v.53 no.3
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• pp.301-305
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• 2016

We investigate proton conduction in a nonstoichiometric ${\Sigma}3$ $BaZrO_3$ (210)[001] tilt grain boundary using density functional theory (DFT). We employ the space charge layer (SCL) and structural disorder (SD) models with the introduction of protons and oxygen vacancies into the system. The segregation energies of proton and oxygen vacancy are determined as -0.70 and -0.54 eV, respectively. Based on this data, we obtain a Schottky barrier height of 0.52 V and defect concentrations at 600K, in agreement with the reported experimental values. We calculate the energy barrier for proton migration across the grain boundary core as 0.61 eV, from which we derive proton mobility. We also obtain the proton conductivity from the knowledge of proton concentration and mobility. We find that the calculated conductivity of the nonstoichiometric grain boundary is similar to those of the stoichiometric ones in the literature.

• Journal of the Korean Ceramic Society
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• v.36 no.8
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• pp.782-790
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• 1999

The compressibility sinterability sintering behaviour and thermal stability of AlOOH added UO2 pellt and PVA-Al(III) complex added UO2 pellet were investigated respectively. Compared with characteristics of AlOOH added UO2 pellet the green density and the sintered density of PVA-Al(III) complex added UO2 pellet were lowered but the grain size and the pore size of that were more increased in accordance with higher compacting pressure. The AlOOH added UO2 pellet had the grain size of about 14${\mu}{\textrm}{m}$ with monomodal pore size distribution while the PVA-Al(III) complex added UO2 pellet had the grain size of about 42 ${\mu}{\textrm}{m}$ with bimodal pore size distribution. The PVA-A(III) complex added UO2 pellet had a similiar open porosity to the AlOOH added UO2 pellet and a lower resintered density change than the AlOOH added UO2 pellet.

• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.51-56
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• 1995

Variation of sintered density of BaTiO3 powder calcined at 120$0^{\circ}C$ and 135$0^{\circ}C$ was investigated with respect to the grain growth behavior. It was found that BaTiO3 powder, which was calcined at 120$0^{\circ}C$, showed abnormal grain growth behavior during sintering process. At initial stage of sintering process, the densification rate of specimen was accelerated with rapid grain growth caused by the abnormal grain growth. But with the increase of sintering time, abnormally grown grain met each other and the density of specimen decreased drastically due to coalescence of pores located in triple junction. On the contrary, BaTiO3 powder calcined at 135$0^{\circ}C$ showed normal grain growth behavior and gradually densified with the increase of sintering time.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 2000.06a
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• pp.65-86
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• 2000

Rare earth-doped ceria powders with a composition of Ce0.8R0.2O1.9(R=Yb, Y, Gd, Sm, Nd and La) were prepared by heating the oxalate coprecipitate. The green compacts began to shrink at 600$^{\circ}$-700$^{\circ}C$. The relative density after the sintering at 1200$^{\circ}$ and 1400$^{\circ}C$ became higher for the higher green density. The samples were densified above 98% relative density by the sintering ant 1600$^{\circ}C$ for 4 h and the grain sizes (4.7-7.6$\mu\textrm{m}$) showed a tendency to become larger with increasing ionic radius of doped-rare earth element. In the intial stag of sintering at 700$^{\circ}$-800$^{\circ}C$, the dominant mass transport process changed from lattice diffusion to grain boundary diffusion to grain boundary diffusion with heating time. The porosity during the intermediated and final stage of the sintering at 1200$^{\circ}$ and 1400$^{\circ}C$ decreased by the mass transport through lattice diffusion with grain growth.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.2
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• pp.90-95
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• 2010

The effects of grain size on the corrosion resistance of 429EM ferritic stainless steels for automobile exhaust system were investigated. Using specimens held at maximum service temperature of $950^{\circ}C$ for 10~70 hours, electrochemical polarization tests were conducted. While corrosion current density, $I_{corr}$, was influenced little by grain size, pitting potential, $E_p$, was increased with an increase of grain size. Sensitizaton at grain boundary occurred when the specimen were held at $950^{\circ}C$ for above 50 hours because of the dissolution of precipitates and grain coarsening.

• Geomechanics and Engineering
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• v.20 no.3
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• pp.243-254
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• 2020

Due to the permanent damage to structures during earthquakes, soil liquefaction is an important issue in geotechnical earthquake engineering that needs to be investigated. Typical examples of soil liquefaction have been observed in many earthquakes, particularly in Alaska, Niigata (1964), San Fernando (1971), Loma Prieta (1989), Kobe (1995) and Izmit (1999) earthquakes. In this study, liquefaction behavior of uniform sands of different grain sizes was investigated by using the energy-based method. For this purpose, a total of 36 deformation-controlled tests were conducted on water-saturated samples in undrained conditions by using the cyclic simple shear test method and considering the relative density, effective stress and mean grain size parameters that affect the cumulative liquefaction energy. The results showed that as the mean grain size decreases, the liquefaction potential of the sand increases. In addition, with increasing effective stress and relative density, the resistance of sand against liquefaction decreases. Multiple regression analysis was performed on the test results and separate correlations were proposed for the samples with mean grain size of 0.11-0.26 mm and for the ones with 0.45-0.85 mm. The recommended relationships were compared to the ones existing in the literature and compatible results were obtained.

• Nuclear Engineering and Technology
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• v.53 no.7
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• pp.2304-2311
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• 2021

The dislocation density in strain-hardened Alloy 690 was analyzed using scanning transmission electron microscopy (STEM) to study the relationship between the local plastic strain and susceptibility to primary water stress corrosion cracking (PWSCC) in nuclear power plants. The test material was cold-rolled at various thickness reduction ratios from 10% to 40% to simulate the strain-hardening condition of plant components. The dislocation densities were measured at grain boundaries (GB) and in grain interiors of strain-hardened specimens from STEM images. The dislocation density in the grain interior monotonically increased as the strain-hardening proceeded, while the dislocation density at the GB increased with strain-hardening up to 20% but slightly decreases upon further deformation to 40%. The decreased dislocation density at the GB was attributed to the formation of deformation twins. After the PWSCC growth test of strain-hardened Alloy 690, the fraction of intergranular (IG) fracture was obtained from fractography. In contrast to the change in the dislocation density with strain-hardening, the fraction of IG fracture increased remarkably when strain-hardened over 20%. From the results, it was suggested that the PWSCC growth behavior of strain-hardened Alloy 690 not only depends on the dislocation density, but also on the microstructural defects at the GB.