• Proceedings of the KWS Conference
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• 2007.11a
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• pp.138-140
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• 2007

This study aimed to evaluate the low temperature properties of the 18Cr ferritic stainless steel weld. Applied welding methods were LB(Laser Beam) and GTA(Gas Tungsten Arc) welding to compare the different low temperature properties of the welds. Low temperature properties were evaluated by the Charpy impact, Erichsen and Expansion test at low temperature. LB weld showed superior low temperature properties in the cases of the Charpy impact test and expansion test at low temperature, while GTA weld showed a superior low temperature property in the case of Erichsen test at low temperature. The different low temperature properties with test methods are still under analysis and may be due to different crack path depending on the microstructure, test speed and stress concentration during test.

• Nuclear Engineering and Technology
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• v.30 no.4
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• pp.377-385
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• 1998

Many nuclear power plants have experienced unscheduled shutdown due to the leakage of steam generator tubes. The leakages are normally due to the crack, possibly stress corrosion cracking (SCC) near the tube expansion at the top of tubesheet or at the tangential point of the row-1 U-bend region. The conventional eddy current technique, which makes use of a differential bobbin coil, has been found to be inadequate for the early detection of SCC. During the in-service inspection, therefore, it is a general practice that the rotating pancake coil (RPC) is used for detecting the cracks. Even in using RPC, however, it is difficult to determine the depth of the cracks quantitatively. This paper attempts to determine the detectability and sizing ability of RPC technique for axial or circumferential cracks at the tube expansion region. The simulated cracks with various dimensions were fabricated by electro-discharge machining (EDM) method. Experimental results are discussed with theoretical calculations.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.36-40
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• 2002

The development of feed drive system with high speed and accuracy has been a major issue in the machine tool industry. Linear motors can be used as the efficient tool to achieve fast feed mechanism and high accuracy. However. a high speed feed drive system with linear motors can generate heat problems such as the variation of temperature distribution and the resultant thermal stress. In this paper, the important heat sources and the resultant thermal errors are presented. The thermal deformation characteristics of the machine tool with linear motors were identified, which are thermal expansion of linear scale, shrinkage, expansion and bending in the machine tool structure.

• Journal of the Korean Ceramic Society
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• v.11 no.3
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• pp.19-26
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• 1974

Mechanical properties of the system PbO-B2O3-V2O5 low melting glass during crystallization by heat-treatment were investigated. Wettability of the system PbO-B2O3-V2O5 was excellent and appropriate for commercial sealing as a low melting solder glass. Crystals, during heat-treated at 30$0^{\circ}C$ of the system PbO-B2O3-V2O5 were $\beta$-4PbO.B2O3, 5PbO.4B2O3, and Pb2V2O7 mainly. The percent of crystallinity was 82$\pm$5%. Mechanical properties of the system PbO-B2O3-V2O5 were influenced not only by the differences of density and coefficient of thermal expansion and the stress induced from the difference in the density and coefficient of thermal expansion between glass phase and crystals but also crystallization conditions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.279-282
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• 2011

The analysis and experimental results for the bellows of gasgenerator liquid oxygen shut-off valve are presented. The analyses are performed using EJMA (Expansion Joint Manufacturing Association) standard and the commercial FE (finite element) analysis program, Abaqus v6.9, at room and cryogenic temperatures. The results include the spring rate, the stress and the fatigue life of the bellows. The effects of the contact and material plasticity on the FE analysis results are also analyzed.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.194-195
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• 2022

The jointing of unsupported concrete on the parking lot floor is a process for cracking and stress relief due to concrete drying shrinkage and restraint, but curling occurs due to long-term drying shrinkage after the initial age. will be lowered Therefore, by using an expansion material and a shrinkage reducing agent, the dry shrinkage of concrete is realized to 200 με or less.

• Coupled systems mechanics
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• v.13 no.2
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• pp.115-132
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• 2024

This paper introduces an improved shear deformation theory for analyzing the buckling behavior of functionally graded plates subjected to varying temperatures. The transverse shear strain functions employed satisfy the stress-free condition on the plate surfaces without requiring shear correction factors. The material properties and thermal expansion coefficient of the porous functionally graded plate are assumed temperature-dependent and exhibit continuous variation throughout the thickness, following a modified power-law distribution based on the volume fractions of the constituents. Moreover, the study considers the influence of porosity distribution on the buckling of the functionally graded plates. Thermal loads are assumed to have uniform, linear, and nonlinear distributions through the thickness. The obtained results, considering the effect of porosity distribution, are compared with alternative solutions available in the existing literature. Additionally, this study provides comprehensive discussions on the influence of various parameters, emphasizing the importance of accounting for the porosity distribution in the buckling analysis of functionally graded plates.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.107-116
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• 2020

The compaction grouting technique is widely used to improve the liquefaction resistance of loose sands that are liquefaction-prone. Particularly, the horizontal injection of compaction grout is proposed for the liquefiable ground with an overlying structure as it does not allow the vertical compaction grouting. However, there has been limited number of researches on the horizontal compaction grouting. Therefore, this study explores the grout bulb shape and expansion direction in loose sand. A series of scaled two-dimensional experiments on the horizontal compaction grouting was conducted varying the overburden stress. The results show that the grout bulb grows in an elliptical shape though its directivity of major axis changes with the overburden effective stress and relative density. The grout bulb expands faster in a horizontal direction under a low overburden stress with a small relative density. The higher overburden stress and the greater relative density cause the more circular shape with the faster expansion in a vertical direction. The presented finding is expected to contribute to accurate and efficient design of the horizontal compaction grouting method.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.499-499
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• 2011

Silicon nanowires (Si NWs) have been extensively studied for nanoelectronics owing to their unique optical and electrical properties different from those of bulk silicon. For the development of Si NW devices, better understanding of oxidation behavior in Si NWs would be an important issue. For example, it is widely known that atomic scale roughness at the dielectric (SiOx)/channel (Si) interface can significantly affect the device performance in the nano-scale devices. However, the oxidation process at the atomic-scale is still unknown because of its complexity. In the present work, we investigated the oxidation behavior of Si NW in atomic scale by simulating the dry oxidation process using a reactive molecular dynamics simulation technique. We focused on the residual stress evolution during oxidation to understand the stress effect on oxidation behavior of Si NWs having two different diameters, 5 nm and 10 nm. We calculated the charge distribution according to the oxidation time for 5 and 10 nm Si NWs. Judging from this data, it was observed that the surface oxide layer started to form before it is fully oxidized, i.e., the active diffusion of oxygen in the surface oxide layer. However, it is well-known that the oxide layer formation on the Si NWs results in a compressive stress on the surface which may retard the oxygen diffusion. We focused on the stress evolution of Si NWs during the oxidation process. Since the surface oxidation results in the volume expansion of the outer shell, it shows a compressive stress along the oxide layer. Interestingly, the stress for the 10 nm Si NW exhibits larger compressive stress than that of 5 nm Si NW. The difference of stress level between 5 an 10 anm Si NWs is approximately 1 or 2 GPa. Consequently, the diameter of Si NWs could be a significant factor to determine the self-limiting oxidation behavior of Si NWs when the diameter was very small.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.952-958
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• 1988

To analyze the nonflatness and residual stress in accelerated cooled plate, a numerical analysis model has been developed. Two factors, i.e. temperature and phase transformation, are considered in calculating the stress distribution that develops during cooling. The plastic strain and plate-buckling, which are often shown in accelerated cooled plate, were determined from this stress. Mean temperature in through thickness direction and temperature difference in width direction are considered in the model to simplify the calculation. The temperature and stress distribution changes caused by phase transformation are involved in terms of the effective specific heat and the effective thermal expansion coefficient. With the model, accelerated cooling of 10mm(t) $^{*}$3000mm(w) plate was simulated. The condition of accelerated cooling was .deg. C/sec from just after hot rolling to 500.deg. C. The initial temperature-difference ratio, .DELTA.Tr, in width direction is an important factor in evaluating the stress distribution. When .DELTA.Tr is 0.08, buckling occurs during cooling and 7kgf/m $m^{2}$ of residual stress develops at the edge of plate. To secure the flatness, .DELTA.Tr should be less than 0.07. Small scaled cooling test was conducted to verify the exactness of the model and the results proved the usefulness of this numerical analysis model.l.