• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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• pp.263-264
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• 2012

In this study, the ultra high strength concrete which have 100, 150, 200MPa took the heat from 20℃ to 70 0℃ and the 0, 20% stress in normal condition's to evaluate stress-strain, residual compressive strength and thermal expansion deformation were evaluated. The heating speed of specimen was 0.77℃/min 20~50℃, 50℃ before the target temperature, and the other interval's heating speed was 1℃/min. As a result, the stress-strain curve of non-load specimen showed the liner behavior at high temperature when the specimen's strength increased more. If ultra high strength concrete got loads, its compressive strength tended to decrease different from the normal strength concrete. The thermal expansion deformation was expanded from a vitrification of quartz over 500℃. however, over the 600℃, it was shrinked because of the dehydration of the combined water.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.9 s.174
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• pp.179-187
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• 2005

The characteristics of blood flow and the interaction between the blood vessel and blood flow play important roles in plaque cap rupture and the growth of atherosclerosis which may lead directly to a heart attack or a stroke. In this study, carotid arteries with different stenoses have been numerically simulated to investigate the wall shear stress(WSS) and the elastic motion of the vessel. Blood flow has been treated as physiological, laminar and incompressible flow. To model the shear thining behavior of the blood, the Carreau-Yasuda model has been employed but the viscoelasticity of blood has not been considered. The results show that the WSS of $severe(75\%)$ stenosis is much higher than those of $25\%\;and\;50\%$ stenosis in the region of stenosis. With the increase in the stenosis thickness, the expansion ratio of the center of the stenosis decreases while the expansion ratio of the upstream region of the stenosis increases.

• Polymer(Korea)
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• v.27 no.3
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• pp.189-194
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• 2003

Interfacial evaluation, damage sensing and cure monitoring of single carbon fiber/thermo setting composite with different curing processes were investigated using electro-micromechanical test. After curing, the residual stress was monitored by measurement of electrical resistance and then compared to various curing processes. In thermal curing case, matrix tensile strength, modulus and interfacial shear strength were higher than those of ultraviolet curing case. The shrinkage measured during thermal curing occurred significantly by matrix shrinkage and residual stress due to the difference in thermal expansion coefficient. The apparent modulus measured in the thermal curing indicated that mechanical and interfacial properties were highly improved. The reaching time to the same stress of thermal curing was faster than that of UV curing case.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1626-1631
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• 2007

The purpose of the study is to simulate the displacement of the LCD glass during process of a large size imprint. During this process, a small temperature variation makes thermal stress, which causes the horizontal variation of mold and glass. During alignment process to fix the LCD glass on a alignment stage, the vertical displacement is made by the absorption pressure and the shear stress. This study simulates the horizontal displacement of mold and glass due to temperature variation, the vertical displacement depending on the shape of absorption surface fixing the LCD glass in the alignment process, and the horizontal and vertical displacement which occurs in the LCD glass at the alignment process. Algor which is a FEM code for a framework simulation was applied. Temperature variation above ${\pm}$ $0.1^{\circ}C$ on mold and glass causes the horizontal displacement of 150nm due to thermal expansion. The vertical displacement due to the circular is ten times of the case of rectangular absorption nozzle. The displacement of the LCD glass in the alignment process is about 49nm.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.145-148
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• 2006

Cold gas dynamic spray is a relatively new coating process by which coatings can be produced without significant heating during the process. Cold gas dynamic spray is conducted by powder sprayed by supersonic gas jet, and generally called the kinetic spray or cold-spray. Cold-spray was developed in Russia in the early 1980s to overcome the defect of thermal spray method. Its low process temperature can minimize thermal stress and also reduce the deformation of the substrate. Most researches on cold-spray have focused on micro scale coating, but our research team tried to apply this method to macro scale deposition. The macro scale deposition causes deformation of a thin substrate which is usually convex to the deposited side. In this research, the main cause of the deformation was investigated using 6061-T6 aluminum alloy and properties of deposited aluminum layer such as coefficient of thermal expansion, Elastic modulus, hardness, electric conductivity were measured. From the result of the analysis, it was concluded that compressive residual stress was the main reason of substrate deformation while CTE had little effect.

• Journal of the Korean GEO-environmental Society
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• v.7 no.5
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• pp.57-66
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• 2006

In this study, the centrifuge model tests were carried out to evaluate the stress concentration ratio, the deformation modes of piles and the ground movement in clay deposit improved by SCP and GCP piles with changing the replacement ratio(20%, 40%, 60%) under flexible loading. Based on the results obtained, it was shown that the stresses acting on GCP was larger than those acting on SCP with the same replacement ratio. It was evaluated that the average stress concentration ratio of soft clay ground improved by GCP was slightly larger than that of SCP when the replacement ratio is 40%. Only expansion failure occurred in GCP, whereas SCP showed the expansion and shear failure simultaneously.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1362-1369
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• 2007

Seoul Metro continuously converted the standard rail into continuous welded rail since the later part of 1990's, and currently, most of the sectors of the Seoul Metro are continuous welded rails. As the continuous welded rail is inhibited by the contraction and expansion force of the rail as well as rail-bed, this force is stored as the internal stress of the rail with the exception of portion of the both ends of the continuous welded rail. If the contraction and expansion of the rail is restricted, the internal stress, that is, the force in the direction of the axis, is proportional to the cross-sectional area of the rail. Therefore, with regards to the temperature changes, the internal stress changes in accordance with the type of rail, bolting apparatus, railroad tie and rail-bed. As such, the rail temperature becomes important data in securing the gap at the adjoining section of the rail in the standard rail section, and to determine the setting temperature for the continuous welded rail. In addition, it becomes basic data for maintenance of the track. Accordingly, this thesis introduces cases of installation of rail temperature detector in order to prevent and manage track defectiveness due to increase in rail temperature, and to utilize as basic data at the time of various construction and maintenance. Furthermore, this thesis aims to assist maintenance of track through systematic temperature management in the future by looking into means of its utilization.

• Journal of Surface Science and Engineering
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• v.48 no.1
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• pp.23-26
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• 2015

What causes the transformation of a solar cell is the behavior difference of thermal expansion occurred between the substrate and the layer of semiconductor used in the solar cell. Therefore, the substrate has to possess a behavior of thermal expansion that is similar with that of semiconductor layer. This study employed electroforming to manufacture Fe-Ni alloy materials of different compositions. To verify the result from a finite element analysis, a two-dimensional Mo substrate was calculated and its verification experiment was conducted. The absolute values from the finite element analysis of Mo/substrate structure and its verification experiment showed a difference. However, the size of residual stress of individual substrate compositions had a similar tendency. Two-dimensional CIGS/Mo/$SiO_2$/substrate was modeled. Looking into the residual stress of CIGS layer occurred while the temperature declined from $550^{\circ}C$ to room temperature, the smallest residual stress was found with the use of Fe-52 wt%Ni substrate material.

• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.21-30
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• 2006

In this study, centrifuge model tests were performed to investigate the stress concentration ratio, bearing capacity and deformation modes of piles in clay ground improved by granular piles with two types of pile (CSCP, SCP) and various replacement ratios (0, 20, 40, 60%). According to the results of tests, the load ratio of ground improved by SCP and CSCP proportionally increased as replacement ratio increased. It shows that average normalized load of ground improved by CSCP is higher by about $8{\sim}21%$ than by SCP. As a result of rigid loading tests, it was evaluated that average stress concentration ratio of CSCP is higher than that of SCP. Only expansion failure occurred in CSCP, whereas SCP showed the expansion and shear failure simultaneously.

• The Journal of Engineering Geology
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• v.31 no.1
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• pp.55-66
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• 2021

Hydraulic-mechanical (H-M) coupled numerical modeling was used to evaluate the evolution of hydrogeological properties in response to the installation and expansion of a borehole. A domain with a discrete fracture network was adopted for discontinuum modeling to simulate changes in fracture apertures. Comparison with real hydraulic test data shows that the effects of principal stress direction and expansion of borehole diameter were reasonably simulated by H-M coupled numerical modeling. The modeling confirmed that aperture changes depended on the principal stress direction, with an increase in aperture size due to vertical displacement being the dominant effect. A concentration of shear dilation around the borehole had an additional, subsidiary, effect on the hydrogeological evolution. These results show that the permeability of fractured rock can be increased by changing the hydraulic properties of a fracture through stress redistribution caused by the installation and expansion of a borehole.