• Journal of the Korea Institute of Building Construction
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• v.9 no.3
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• pp.103-107
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• 2009

It is necessary to develop a new technology for effectively controlling thermal crack caused hydration heat according to the increasing construction of large size massive concrete structures such as mat foundation of high-rise building. Therefore, to develop a new technology for reducing hydration heat of large size massive concrete in this study, it was investigated hydration heat generation properties of binder using latent heat materials. As a test result, it was confirmed that latent heat materials were advanced on the reduction of hydration heat and control of thermal crack. It is expected to be applied as the excellent technology on the management of hydration heat and thermal crack in large size massive concrete structures.

• Advances in concrete construction
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• v.12 no.5
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• pp.439-450
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• 2021

In recent years, nano-reinforcing materials are widely utilized in cement composites due to their unique multifunctional properties. This study incorporated multi-walled carbon nanotubes (MWCNTs) into the cementitious composites at ratios of 0.1%, 0.3%, and 0.5%, and investigated their influence on the flowability, mechanical strength, and hydration heat properties. The addition of MWCNTs enhanced the compressive and split tensile strengths approximately by 18-51%. In the semi-adiabatic temperature rise test, the internal hydration heat of the composites reduced by 5%, 9%, and 12% with the increase of MWCNTs in 0.1%, 0.3%, and 0.5%. This study further performed hydration heat analysis and estimated the adiabatic temperature rise, thermal stress, and thermal crack index. The internal hydration heat of the concrete decreased by 5%, 10%, and 13% with the increase of MWCNTs. The thermal stress of the concrete decreased with increase in the addition of MWCNTs, and the obtained temperature crack index was effective in controlling the thermal cracks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.2
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• pp.91-101
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• 2006

Lately, massive concrete structures are increasingly built. In such massive structures, the heat of hydration of mass concrete causes thermal cracks. To avoid thermal crack, methods widely acceptable for practical use are pre-cooling, pipe cooling and control of placing height. Thermal stress analysis is performed to find the way of controlling the thermal crack of pier footing mat in this paper. The footing mat model for the analysis is $12m{\times}14m$area and 3m height. The analysis results are compared with method of control of lift height and method of pipe cooling. The analysis results show that thermal crack can be removed by method of placing control and pipe cooling at footing mat placed on the ground.

• Tunnel and Underground Space
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• v.20 no.1
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• pp.65-72
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• 2010

Crack-controlled blasting method which utilizes notched charge hole has been proposed in order to achieve smooth fracture plane and minimize the excavation damage zone. In this study, the blast models, which have a notched charge hole, were analyzed using dynamic fracture process analysis software to investigate the effect of the geometry of a notched charge hole and decoupling indexes of the charge hole on crack growth control in blasting. As a result, crack extension increased and damage crack decreased with the notch length. Ultimately, stress increment factors and resultant fracture patterns with different notch length and width were analyzed in order to examine the effect factors on the crack growth controlling in rock blasts using a notched charge hole.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.111-116
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• 1996

IGSCC(Intergranular stress corrosion cracking) behaviors of Alloy 600 were studied by the electrchemical ten methods of controlling specimens electrode potentials in the active-passive transition region of anodic polarization curve. Anodic polarization and static potential tests of stressed C-ring type MA Alloy 600 were carried out in 10% NaOH at 300 $^{\circ}C$ for 7days. It was confirmed that IGSCC of Alloy 600 was accellerated by maintaining the specimen potential in the susceptible active-passive transition region of anodic polarization curve. An intergranular crack was initiated on the surface area of C-ring specimens where protective oxide layer was broken down. And the depth of the crack growth was about 100 ${\mu}$m during the testing periods.

• Journal of Ocean Engineering and Technology
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• v.11 no.1
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• pp.16-23
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• 1997

Stainless steel are widely applicable in various engineering fields for its exellent corrosion and impact ressistance. Austenitic weld metal has some ferrite for preventing solidification cracking by ASME specification. Several family of austenic stainless steel contains varying ferrite contents. But ferrite in austenic stainless steels is adversely affect weld metal toughness and since fully austenic grades are known to have good toughness. Austenic stainless steel has various alloying addition for improving corrosion resistance, impact toughness and solidification crack resistance. The effect of various alloying elements are not found to be clear in present. From this view of point, this study tried to establish the criteria of alloy design for austenic stainless steel by controlling primary solidification mode and clarifying the effect of several alloying elements.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.503-506
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• 2000

YBCO superconducting thick films were prepared on Ag wire by electrophoresis in acetone and ethanol with chemically modified suspension. The addition of organic compounds, such as PEG, EG into suspension solution for improving critical current density was investigated. Surface state, deposition condition, pore distribution and cracks were investigated by using SEM photographs. Controlling preparation conditions were studied for reducing these defects. As a results, in acetone solution, the surface crack of samples was decreased with increasing PEG. On the contrary, the surface crack of sample was increasing with increasing the amount of EG. In ethanol solution without I$_2$, which was generally used for an electrolyte, the deposition time was longer than this of acetone. For that reason the sample deposition in ethanol time was needed with enough stirring time for suspending YBCO powder and deposition time.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.227-228
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• 2023

This study is tocompare and analyze the results of hydration heat analysis and on-field measurements using the method with hydration heat difference and insulation curing method for controlling hydration heat in mass concrete. As a result of the analysis, the temperature difference between the center and the surface was predicted very similarly, and the mass concrete surface was controlled to a safe level when evaluating with a temperature crack index, and after being finished, it was confirmed that there was no hydration crack.

• Journal of the Korean Ceramic Society
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• v.51 no.5
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• pp.399-405
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• 2014

Porous alumina with different porosities, 5.2 - 47.5%, were coated with cover-glass having a thickness of $160{\mu}m$, using epoxy adhesive. We investigated the effect of the porosity of the substrate layer on the crack initiation load, and the size of cracks propagated in the coating layer. Hertzian indentations were used to evaluate the damage behavior under a constrained loading condition. Typically, two types of cracks, ring cracks and radial cracks, were observed on the surface of the glass/porous alumina structure. Indentation stress-strain curves, crack initiation loads, crack propagation sizes, and flexural strengths were investigated as a function of porosities. The results indicated that a porosity of less than 30% and a higher substrate elastic modulus were beneficial at suppressing cracks occurrence and propagation. We expect lightweight mechanical components with high strength can be successfully fabricated by coating and controlling porosities in the substrate layer.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.6
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• pp.627-634
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• 2007

A bonded plate or a coated part can be debonded by external impact or thermal expansion. To analyse adhesive strength, the blister test is generally adopted. In this paper, a blister test is modelled theoretically and then the stability and bifurcation of the blister are studied under several different cases. The blister is simplified to consist of a pure bending plate attached elastically to the rigid substrate. Expression of the energy release rate is obtained as a form of an explicit function for a circular-type blister or tunnel-type blister grown by controlling the internal pressure or internal volume. Stability and bifurcation are also studied in the frame of the quasi-static evolution. The study shows that the circular- type blister propagates with the first mode of bifurcation and that the tunnel-type blister propagates with a regular wave. It is proved that the waves have the same form on two side lines of the tunnel and that the wave length can be obtained. When the internal pressure is controlled, the blister is unstable, but when the internal volume is controlled, it is stable.