• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.131-135
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• 2001

Evaluation of microstructural changes during open die forging of heavy ingots is important for process control. The objective of the control of forging parameters, such as shape of the dies, reduction, temperature and sequence of passes, is to maximize the forging effects md to minimize inhomogeneities of mechanical properties. The hot working die steel is produced by using the multistage open die forging. The structure is altered during forging by subsequent processes of plastic deformation, recrystallization and grain growth. A numerical analysis using an rigid visco-plastic finite element model was performed to predict microstructural evolution of hot working die steel.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.82-82
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• 2014

One of the subjects in clouds' structure and development is small scale structure of interstellar cloud. The possibility of AU scale structure (Marscher et al. 1993; Moore & Marscher 1995; Roy et al. 2012) is discussed, and this small scale structure is considered as the result of hydrogen volume density (Moore & Marscher 1995), or small-scale chemical and other inhomogeneities (Liszt & Lucas 2000). In order to study this subject with emission line, extremely high resolution is mandatory by VLBI system. However, the alternative method could be observing the absorption line of interstellar cloud on the continuum object. In this case, the resolution would be restricted to the size of the continuum object, if the size of the object is smaller than the resolution of a used telescope. We observed the previous researchers' three objects (BLLAC, NRAO150, B0528+138), whose spectrums are changed from 1993 to 1998 (Liszt & Lucas 2000), with KVN. Through KVN observation, we found the changes of optical depth spectrum compared with the previous spectrums. We will discuss the optical depth spectrum variation by time variation and the meaning of it.

• Journal of Ocean Engineering and Technology
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• v.14 no.3
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• pp.46-54
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• 2000

Three dimensional numerical experiments that included the land-use transformation by the large scale reclamation were used to investigate the mesoscale air flow over the coastal regions. In this paper the surface temperature of the inland was determined through the surface heat budget consideration with inclusion of a layer of vegetation. The vertical diffusion coefficients of momentum, heat and specific humidity in the constant flux layer were taken from the Mellor and Yamada(1975). It has shown that the resulting model is able to reproduce the air circulation in coastal regions, and the simulated characteristics agree with the known properties of this circulation. A series of numerical experiments were then carried out to investigate the diurnal response of the air flow to various types of surface inhomogeneities.

• Journal of Mechanical Science and Technology
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• v.19 no.11
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• pp.2025-2031
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• 2005

Eshelby type micro mechanics model with a newly developed piezoelectric Eshelby tensor is proposed for predicting the effective electroelastic properties of the piezoelectric composite. The model is applied for piezoelectric solids containing both porosities and metal inhomogeneities. The effective electroelastic moduli of the composites such as stiffness, piezoelectric constants, and dielectric constants are predicted by the present model, which are extensively compared with the existing experimental results from the literatures. The validity of Eshelby type model for predicting the effective properties of the composite is thoroughly examined. It can be concluded from this study that a new mechanism is needed to compute correctly the dielectric constants among the effective properties of the composites.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.85-88
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• 1997

The effect of lubrication on the evolution of the cold rolling texture in low carbon steels was studied by X-ray texture measurement. The cold rolling texture was inhomogeneous through the thickness of the rolling sheet. The type and sharpness of the texture through the thickness and the degree of inhomogeneity were found to be dependent on the friction acting between rolls and the rolled materials. The degree of the through thickness inhomogeneities was higher in the specimen rolled without lubrication. The friction acting on the roll surface led to the formation of the Goss-Orientation in the rolling texture.

• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.84-88
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• 2002

The resistive fault current limiter (SFCL) is a very attractive device for power networks. But it has a serious Problem in using YBCO films for fault current limiter is inhomogeneities caused by imperpect manufacturing. So simultaneous quenches are a difficult problem which elements for current limiting are connected in series for increasing voltage ratings. We investigated extended electric field-current characteristics for current limiting element of YBCO film when O-130mT magnetic field is applied. And quench characteristics were investigated in over all element and between elements of YBCO films. From the experiments, it was shown that applied magnetic fields using solenoid coil induced uniform quench distribution for over all stripes and simultaneous quench in all elements for current limiting of YBCO film was realized. We have achieved resistive fault current limiter of 1.2kV/20A rating using magnetic field.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.134-140
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• 2014

The paper presents an overview of the present state of study on the fatigue behaviors at very high number of cycles ($N_f$ > $10^7$). A classification of materials with typical S-N curves and influencing factors such as notches, residual stresses, temperatures, corrosion environments and stress ratios are given. The microstructural inhomogeneities of materials and micro-cracks played an important roles in very high cycle fatigue behaviors. The failure mechanisms for the fatigue design of materials and components are mentioned.

• Transactions of Materials Processing
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• v.9 no.2
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• pp.193-202
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• 2000

The influence of rolling draughts on the formation of through-thickness textures in aluminum 5000X sheet was investigated by X-ray texture measurements and microstructure observations. In order to intensify the deformation inhomogeneities, cold rolling was performed without lubrication. Applying a large draught gave rise to the formation of the shear texture at the surface, whereas a normal plane strain testure formed at the surface after deformation with a small draught. The orientation density along the $\beta$-fiber orientations which developed in the center layer of the rolled specimen was also dependent on the strain gradients in a roll gap. Upon annealing, the deformed substructure of sample surfaces was transformed into a fine grained recrystallized microsturcture through extended recovery reaction. However, coarse grains developed after the discontinuous recrystallization which gave rise to the development of the Cube-texture.

• Macromolecular Research
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• v.9 no.6
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• pp.319-326
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• 2001

Fatigue crack growth (FCG) behavior of natural rubber/ethylene-propylene-diene rubber (NR/EPDM) blend vulcanizates under dynamic tearing condition was investigated by using a fracture mechanics approach. It appeared that variation of crack growth rate with blend compositions was dependent on the level of imposed tearing energy G. At low tearing energy region, the FCG rates of the blend were lower as the EPDM content was increased, while at high tearing energy region, the trend was reversed. Over the measured range of tearing energy G, all blend compositions showed the lower crack growth rates compared to the average of properties of component elastomers. When the blends were thermally aged, the fatigue resistance of the blends was deteriorated in proportion to the concentration of EPDM phase. Fatigue crack growth behavior of the blends was supposed to be associated with the inhomogeneities of the crosslink structure of the blends arising from cure incompatibility of the EPDM and NR when they are sulphur cured.

• Advances in materials Research
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• v.13 no.1
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• pp.37-53
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• 2024

This paper presents a careful theoretical investigation into interfacial stresses in RC beams strengthened with externally bonded imperfect FGM plate. In this study, an original model is presented to predict and to determine the stresses concentration at the imperfect FGM end, with the new theory analysis approach. Stress distributions, depending on an inhomogeneity constant, were calculated and presented in forms. It is shown that both the shear and normal stresses at the interface are influenced by the material and geometry parameters of the composite beam, and it is shown that the inhomogeneities play an important role in the distribution of interfacial stresses. The theoretical predictions are compared with other existing solutions. The numerical resolution was finalized by taking into account the physical and geometric properties of materials that may play an important role in reducing the stress values. This research is helpful for the understanding on mechanical behaviour of the interface and design of the PFGM-RC hybrid structures.