• Computers and Concrete
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• v.11 no.4
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• pp.337-350
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• 2013

The sensitivity of compressive strength of no-slump concrete to its ingredient materials and proportions, necessitate the use of robust models to guarantee both estimation and generalization features. It was known that the problem of compressive strength prediction owes high degree of complexity and uncertainty due to the variable nature of materials, workmanship quality, etc. Moreover, using the chemical and mineral additives, superimposes the problem's complexity. Traditionally this property of concrete is predicted by conventional linear or nonlinear regression models. In general, these models comprise lower accuracy and in most cases they fail to meet the extrapolation accuracy and generalization requirements. Recently, artificial intelligence-based robust systems have been successfully implemented in this area. In this regard, this paper aims to investigate the use of optimized support vector machine (SVM) to predict the compressive strength of no-slump concrete and compare with optimized neural network (ANN). The results showed that after optimization process, both models are applicable for prediction purposes with similar high-qualities of estimation and generalization norms; however, it was indicated that optimization and modeling with SVM is very rapid than ANN models.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.69-75
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• 2017

Ultra-high performance concrete and high ductile cementless composite are considered as promising construction materials because those exhibits higher performance in terms of high strength and high ductility. The purpose of this study is to investigate experimentally the compressive strength and tensile behavior of ultra-high performance concrete and high ductile cementless composite. A series of experiments including density, compressive strength, and uniaxial tension tests were performed. Test results showed that the compressive strength and tensile strength of alkali-activated slag based high ductile cementless composite were lower than those of ultra-high performance concrete. However, the tensile strain capacity and toughness of alkali-activated slag based high ductile cementless composite were higher than those of ultra-high performance concrete. And it was exhibited that a high ductility up to 7.89% can be attainable by incorporating polyethylene fiber into the alkali-activated slag based cementless paste.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.6
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• pp.390-395
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• 2015

Molded insulation materials are widely used from large electric power transformer apparatus to small electrical machinery and apparatus. In this study, by adding MgO with the average particle of several tens nm and the excellent thermal conductivity into molding material, we improved the problem of insulation breakdown strength decrease according to rising temperature in overload or in bad environmental condition. We confirmed the life evaluation by using the insulation breakdown and inverse involution to investigate the electrical characteristics of nano-composites materials. By using a scanning electron microscope, it is confirmed that MgO power with the average particle size of several tens nm is distributed and the filler particles is uniformly distributed in the cross section of specimens. And it is confirmed that the insulation breakdown strength of Virgin specimens is rapidly decreased at the high temperature area. But it is confirmed that the insulation breakdown strength of specimens added MgO slow decreased by thermal properties in the high temperature area improved by the contribution of the heat radiation of MgO and the suppression of tree. The results of life prediction using inverse involution, it is confirmed that the life of nano-composites is improved by contribution of MgO according to the predicted insulation breakdown strength after 10 years of specimens added 5.0 wt% of MgO is increased about 2.9 times at RT, and 4.9 times at $100^{\circ}C$ than Virgin specimen, respectively.

• Korean Journal of Materials Research
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• v.14 no.8
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• pp.579-586
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• 2004

A study on the effects of oxide growth on the mechanical properties degradation of pure zirconium and Zircaloy-4 is carried out with high temperature tensile tests. It is found that the mechanical properties can deteriorate with the oxide growth less than $1\%$ of total specimen cross section, especially at $300\~400^{\circ}C$ that is zirconium alloy cladding temperature during the nuclear reactor operation. It is also revealed that Young's modulus changes little but yield strength and tensile strength drop down to $20\% and 40\%$ of the room temperature strength, respectively, in the temperature range. Fractographic analysis shows that the number of dimples decreases and fractured surface becomes smooth with increasing oxide thickness.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.692-697
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• 2004

This study is on the increasement of strength about soft ground improvement material using waste residual(paper fly ash, coke ash, slag) by fire. Through this study the authors have analyzed the strength improvement of mixed soft silty sand with improvement materials. The strength of mixed soils with high mixture ratio and more curing days increased. But CA-30(cokes 60%) make more low strength improvement than others. Therefore the authors find out that paper fly ash+cokes, paper fly ash+slag or cokes+slag improvement material is more effect in improvement of soft silty sand than cokes+cenlent. And Ettringite reaction is free mixed soils with more than two materials.

• International Journal of Concrete Structures and Materials
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• v.3 no.2
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• pp.97-101
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• 2009

It has been known that acid-resistant concretes on the liquid glass basis have high porosity (up to 18${\sim}$20%), low strength and insufficient water resistance. Therefore they can not be used as materials for load-bearing structural elements. Significant increasing of silicate matrix strength and density was carried out by incorporation of special liquid organic alkali-soluble silicate additives, which block of superficial pores and reduces concrete shrinkage deformation. It was demonstrated that introduction of tetrafurfuryloxisilane additive sharply increases strength, durability and shock resistance of silicate polymer concrete in aggressive media. This effect is attributable to hardening of contacts between silicate binder gel globes and modification of alkaline component owing to "inoculation" of the furan radical. The optimal concrete composition with the increased strength, chemical resistance in the aggressive environments, density and crack resistance was obtained.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.83-87
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• 2002

Aerospace industries are widely using honeycomb sandwich structures that it has high specific strength and stiffness, chemical material resistance and fatigue resistance. But, in repairing process of damaged areas, one of the problems is that delamination can be occurred in the sound areas during and/or after the exposure to the elevated curing temperature in case that the repair process is repeated. Therefore, this study was conducted Flatwise tensile, Drum peel and Long beam flexural strength tests to evaluate the degree of degradation of mechanical properties of the honeycomb sandwich structures by affecting thermal aging. As the results, the decrease of mechanical strength was observed at the specific specimen which is exposed over 50hrs at $127^{\circ}C$.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.6
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• pp.658-663
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• 2009

Metal/ceramic composites structures have many attractive properties with great potential for applications that demand high stiffness as well as chemical and biological stability, thermal and electrical insulation. They are currently in use for mechanical and thermal protection in cutting tool and engine parts. Thus, determination of adhesive properties for coating part is one of the most important problems for the extension of the use of coated materials. In this work, bending strength of Functionally Graded Materials(FGM) are evaluated by means of bending strength tester. The graded layer according to the load condition showed the change of the bend strength.

• Transactions on Electrical and Electronic Materials
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• v.14 no.2
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• pp.105-109
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• 2013

In order to develop high voltage (HV) insulation materials, epoxy/spherical alumina composites with two different particle sizes (in ${\mu}m$) were prepared and a dynamic mechanical analysis (DMA) and electrical insulation breakdown strength test were carried out in sphere-sphere electrodes and the data were estimated using Weibull statistical analysis. Alumina content varied from 50 to 70 wt%. The electrical insulation breakdown strength for epoxy/alumina (50 wt%) was 44.0 kV/1 mm and this value decreased with increasing alumina content. The effects of insulation thickness and alumina particle size on the insulation breakdown strength were also studied. The insulation thickness varied from 1 mm to 3 mm, and the particle sizes were 7.3 or $40.3{\mu}m$.

• Transactions of Materials Processing
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• v.7 no.6
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• pp.530-538
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• 1998

Elimination of the heat treatment process is very important in automation of metal forming since controlling heat treatment by computer has many difficulties and it has bottle neck problem. non-heat-treated steels materials which are not in need of heat treatment have been developed for cold forging. However to apply non-heat-treated steel to structural parts. it is necessary to prove reliability of mechanical properties. In order to define the reliability of mechanical properties we have investigated microstructure, hardness, the tensile strength compressive strength and tensile fatigue strength for both steels. Considering the results of high cycle fatigue test for both specimen the characteristics of non-heat-treated steel are decided on the yield strength, It has same tendency for heat-treated steel. Therefore non-heat-treated steel which has the appropriate yield strength may be applied in cold forging.