• KOREAN JOURNAL OF CROP SCIENCE
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• v.48 no.3
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• pp.142-146
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• 2003

To obtain information on the inheritance of grain weight and grain size of japonica cultivar, Sobibyeo which has high yielding potential and large grain in rice, the genetic variation, heritability and phenotypic correlation of 1,000 grain weight, grain length, width and thickness were investigated in two crosses, Iksan 429/Sobibyeo and Iksan 430/Sobibyeo. The gram characteristics of $\textrm{F}_1$ hybrids exceeded mid-parental values, while grain length: width ratio was intermediate between the parents. In $\textrm{F}_2$ populations, the average grain length, width and thickness were intermediate as mid-parental values, but grain weight exceeded the mid-parental values. In $\textrm{F}_2$ populations of Iksan 429/Sobibyeo and Iksan 430/Sobibyeo, mean 1,000 grain weights were 24.86g and 25.04 g on the average, and ranged 18.4g-32.2g and 19.5g-33.4g, respectively. The segregation mode for grain weight was regarded as a nearly normal distribution in two crosses of $\textrm{F}_2$ populations. Estimates of broad sense heritabilities for grain weight in Iksan 429/Sobibyeo and Iksan 430/Sobibyeo were high as 89.00% and 89.06%, and grain length showed the highest heritability among grain characteristics as 97.45% and 97.35%, respectively. Grain weight was highly correlated with grain length, width and thickness, and grain length was highly correlated with grain width and thickness. These grain characteristics were apparently controlled by polygenes. Accordingly, these traits will be readily improved through selection in the early segregating generations.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.123-126
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• 2003

A high strength aluminum alloy bolt (A7050, T7 temper treatment) has been developed by the authors. The bolt has a small grain size in the whole area of the bolt because of the large equivalent strain followed by thermo-mechanical treatment. As the bolt made of A 7050 has a risk of stress corrosion cracking, each grain should be strengthened the grain inside than the grain boundary in order to improve the stress corrosion cracking resistance. It has been confirmed that the nano-indentation hardness at each grain inside increased with the increasing equivalent strain by thermo-mechanical treatment processing.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.865-869
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• 1997

In recent years, there has been increasing demand of ultra-fine grain graded cemented tungsten carbide material with high hardness and toughness which is used as high speed cutting tool for development in semiconductor, electronics and die/mold industry, which bring into limelight high-precision, high-efficient machining of sculptured surfaces. This paper deals with the performance of variation in the ultra-fine grain graded cemented tungsten carbide material such as grain size, hardness and density varied according to the volume of added elements, Co or TaC, and he changing of mixing, sintering process. Also, the performance of developing material with uniformed grain size of 0.5${\mu}{\textrm}{m}$ is compared with other domestics' & foreign companies' with analyzing and cutting performance testing.

• 전기의세계
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• v.31 no.6
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• pp.437-444
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• 1982

Although several kinds of conduction mechanism of PTC thermistor have been reported, there were few satisfying results. In this paper, the reported conduction mechanism theories were scrutinized and analyzed by using the experimental results. PTC thermistors for this study were manufactured by adding Sb$\_$2/O$\_$3/, AI$\_$2/O$\_$3/, TiO$\_$2/, and SiO$\_$2/ to BaTiO$\_$3/, and by sintering it at different temperatures. In order to analyze the conduction mechanism, R-T characteristics and its frequency dependence of specimens were measured. And also, the structures of specimens were studied. Especially this paper emphasized the explanation of the resistivity characteristics as the grain growth state of PTC thermistor specimens with respect to soaking temperature. According to the results, the resistivity of PTC thermistor whose grain was formed by semiconducting, was independent to the grain size at room temperature. For small and uniform grain size, the slope of the resistivity near the Curie temperature and the resistivity above the Curie temperature became greater and PTCR effect was improved.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.466-469
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• 2002

In the sintering of YIG, abnormal grain growth phenomena was observed. This abnormal grain growth is related to the sintering temperature in this experiment. In the sintering below 145$0^{\circ}C$., the sintered body showed narrow size distribution. However, in the sintering at 145$0^{\circ}C$, a few grains grew rapidly with respect to other grains, and bimodal size distribution was appeared. Liquid phase was not observed far from the abnormally grown large grains, but only near the large grains. This means that the abnormal grain growth was caused by the nonuniform distribution of liquid phase which promote the grains growth. This nonuniform distribution of liquid phase was thought to be due to the nonuniform mixing of the starting materials. This abnormal grain growth was suppressed by enhance the compositional uniformity by multiple calcination.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.11
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• pp.1844-1853
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• 2001

In the present investigation, it was attempted to design the rolling pass schedule fur a clean steel of 0.1C-1.5Mn-0.25Si with the objective of the austenite grain refinement. As the method of approach, a coupled mathematical modeling technique was proposed which consists of a recrystallization model and a flow stress modes. The validity of the coupled model was examined through comparison with results of continuous and discontinuous compression tests at various temperatures, strains and strain rates. The coupled model was incorporated with the finite element method to set up a systematic design methodology far the rolling path schedule for austenite grain refinement. Two path schedules were obtained and discussed in the paper with regard to rolling path time, average grain size, grain size deviation in thickness, etc.

• Journal of Powder Materials
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• v.8 no.3
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• pp.168-173
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• 2001

The effect of grain refinement of the strength and ductility of metallic materials is investigated. A model in which a single phase material is considered as an effectively two-phase one is discussed. A distinctive feature of the model is that grain boundaries are treated as a separate phase deforming by a diffusion mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanisms: dislocation glide and mass transfer by diffusion. The model was exemplified by simulating uniaxial tensile deformation of Cu down to the nanometer grain size. The results confirm the observed strain hardening behaviour and a trend for reduction of ductility with decreasing grain size at room temperature.

• 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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2837-2845
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• 1994

Several methods have been developed to predict on the remaining life of the old power plants. However, Larson-Miller parameter, one of existing creep life prediction methods, has not reflected the effect of material degradatioin and grain size. So this study has been carried out to research the effects of material degradation and austenite grain coarsening on the life prediction of 3.5Ni-Cr-Mo-V steel. An experimental result shows that carbide coarsening has no significant effects on the creep rupture life and the Larson-Miller parameter, but grain coarsening has an important influence on the creep ruptrure life and the Larson-Miller parameter. Therefore Larson-Miller constant, K should be determined to consider on the chemical composition and the grain size of materials.

• Geomechanics and Engineering
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• v.2 no.4
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• pp.303-319
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• 2010

The effect of grain crushing on the deformation of sand in 1D compression and 1D creep at high stresses was investigated theoretically and experimentally. An approach was proposed to formulate the process of grain crushing in sand in accordance with the laws of fracture mechanics and energy conservation. With this approach, the relation between the void ratio and the amount of grains crushed in 1D compression was derived. Laboratory test data were used to verify this derived relation. In addition, it was observed that there are similarities in evolution of grain size distribution in 1D compression and 1D creep tests. This implies that the changes in microstructure in sand under 1D compression and 1D creep are comparable.