• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1005-1008
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• 2008

The purpose of this study is to estimate basic mechanical properties of alkali-activated concretes based on GGBS(Ground Granulated Blast Furnace Slag). In this study, various mix ratios of alkali activated concretes based on sodium silicate and GGBS were set to evaluate concrete's compressive strengths and strains on the basis of results of existing alkali-activated cements and preliminary concrete tests, which were already performed by authors [Ref. 1]. Compressive strengths of concretes of ages 1, 3, 7, 28, 56 and 91 days were tested and investigated, respectively, and at early ages (< 7days) alkali-activated slag concrete (AASC) showed a high strength development, compared to that of Ordinary Portland Cement (OPC). A compressive strengths of AASC at age-3days range between 18 and 24 MPa, while those of OPC range 12 and 15 MPa. The stress-strain curve after maximum stress, on the other hand, is approximately reached at a compressive strain between 0.002 and 0.0025, which mechanical property is very similar to that of OPC.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.47.2-47.2
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• 2014

Several studies have reported the presence of sodium excess objects having neutral atomic absorption lines at $5895{\AA}$ (NaD) and $8190{\AA}$ that are deeper than expected based on stellar population models that match the stellar continuum. The origin of these lines is therefore hotly debated. van Dokkum & Conroy proposed that low-mass stars (0.3M) are more prevalent in massive early-type galaxies, which may lead to a strong NaI 8190 line strength. It is necessary to test this prediction, however, against other prominent optical line indices such as NaD, Mgb, and Fe5270, which can be measured with a significantly higher signal-to-noise ratio than NaI 8190. We identified a new sample of roughly one thousand NaD excess objects (NEOs; ~8% of galaxies in the sample) based on NaD line strength in the redshift range 0.00$H{\beta}$ line strengths and significant emission lines, which are indicative of the presence of young stellar populations. This result implies that the presence of the interstellar medium and/or dust contributes to the increase in NaD line strengths observed for these galaxies.

• Tribology and Lubricants
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• v.39 no.5
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• pp.190-196
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• 2023

Anti-adhesion coatings are very important in the processing of adhesive materials such as optical clear adhesive (OCA) films. Choosing the appropriate release coating material for dies and tools can be quite challenging. Hydrophobic surface treatment is usually performed, and its performance is often estimated by the static water contact angle (CA). However, the relationship between the release performance and the CA is not well understood. In this study, the water CAs of surfaces coated with anti-adhesion materials and the peel strengths of the acrylic-based adhesive films are evaluated. STC5 and SUS304 are selected as the base materials. Base materials with different surface roughnesses are produced by hairline finishing, mirror-polishing, and end milling. Four fluoropolymer compounds, including a self-assembled monolayer, are selected to make the base surface hydrophobic. Static, advancing, and receding CAs are mostly increased due to the coating, but the CA hysteresis is found to increase or decrease depending on the coating material. The peel strengths all decreased after coating and are largely dependent on the coating material, with significantly lower values observed for fluorosilane and perfluoropolyether silane coatings. The peel strength is observed to correlate better with the static CA and advancing CA than with the receding CA or hysteresis. However, it is not possible to accurately predict the anti-adhesion performance based on water CA alone, as the peel strengths are not fully proportional to the CAs.

• Composites Research
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• v.13 no.1
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• pp.33-39
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• 2000

A numerical approach for predicting the ultimate strength of laminate composites has been studied using the Weibull distribution of the strengths of lamina plies. The probabilistic initial failure strengths of laminates were calculated using Tsai-Hill failure criterion. The ultimate strength of the laminate composites has been predicted using progressive failure analysis. The experimental results show that the strength prediction based on the Weibull distribution of ply strength reasonably agrees well with the experimentals better than equal strength assumption.

• Journal of Korean Institute of Industrial Engineers
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• v.39 no.5
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• pp.383-392
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• 2013

Taguchi method is a technique widely used in industries to attain a reliable quality even under existence of various noise variables. Basically, it relies on the interactions between the controllable and the noise factors. Under insignificant interactions between the design parameters and noises, the effectiveness of Taguchi methodology will be doubtful. Furthermore, existence of strong interactions among controllable factors may undermine the power of Taguchi approach. An abundant crop may be expected by a well planned Taguchi approach. A well designed set of experiments is one of the important prerequisites for its successful result. For this, we must have a clear understanding on strengths and weaknesses of Taguchi methodology together with a sound knowledge on the applicable system. This study provides some insights on Taguchi approach based on two case examples of one successful and the other unsuccessful. Eventually, this research aims to facilitate deeper understanding and right application of Taguchi methodology in industries.

• Journal of the Korean Society of Safety
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• v.32 no.5
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• pp.69-75
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• 2017

Structural safety evaluation for static strength of thin plate RC member with high strength concrete is conducted in this study. Static strengths were predicted and compared with the experimental values. Predicted values were calculated by the evaluation formula based on the punching shear behavior and the yield line theory which can appear in the plate members. Static load tests were carried out for the specimens with high strength concrete and the test results were compared with the required performance in design. The comparison results show that the specimens with high strength concrete have sufficient structural safety for flexural and punching shear performance required in design. High strength concrete specimens exhibited excellent strength despite their small thickness. The range of concrete strengths applied in this study was about 60 MPa to 100 MPa.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.163-168
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• 2001

A FEM-based analytical approach was used to evaluate the fatigue strength of a KHST gangway. A KHST gangway was made of AC4C, 5083-O, 6005A-T6 aluminum alloys. The fatigue strengths of them were obtained from the related code and literatures. The effect of tensile mean stress was taken into account by the modified Goodman diagram, but the effect of compressive mean stress was not considered. There was not any location of a KHST gangway that exceeded the allowable fatigue strengths.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.253-259
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• 1996

The purpose of this study is to investigate the fundamental properties of polyurethan concrete. Polyurethane must be expanded by means of a blowing agent during polymerization. Chemical blowing is caused by the reaction water with isocyanate. Binder system for polyurethane concrete is based on polyol and isocyanate with catalyst, surfactant, and methyl chloride. Polyurethane concretes are prepared with various grading of aggregate, and tested for compressive, flexural strengths, flow test, foaming multiple proportion, working life, condition of surface, distirbution of aggregate. From the test results, the foaming of polyurethane concretes are affceted by amount and grading of aggregate. Workability increases with raising amount of methy chloride and working life reduced according to amount of catalyst. The mix proportion of B with methyl chloride of 1% and catalyst of 0.1g for polyurethane concrete is recommended in consideration of strengths, condition of surface and balance between cost and performance.

• Computers and Concrete
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• v.6 no.1
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• pp.59-78
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• 2009

Reliability analysis for a proposed limit state bridge design code is performed. In order to introduce reliability concept to design code, the proposed live load model is based on truck weight survey. Test data of domestic material strengths are collected to model statistical properties of member strengths. Sample RC and PSC girder sections are designed following the safety factor format of the proposed code and compared with the current design practice. Reliability indexes are calculated and examined for material and member resistance factor formats and sample calibrations of safety factors are presented. It is concluded that the proposed code provides reasonable level of reliability compared to the international design standards.

• Elastomers and Composites
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• v.50 no.3
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• pp.205-209
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• 2015

Magnesium oxide (MgO) reinforced polyamide-66 (PA66) composites were prepared through melt-compounding method in order to determine the possibility of using MgO particle as conductive filler in the polymer-based composite. The effects of MgO filler content on the thermal conductivity and mechanical properties for the PA66/MgO composites were investigated. The results showed that the addition of MgO filler to the PA66 matrix led to a large increase in thermal conductivity of the PA66/MgO composites. Tensile strengths of the PA66/MgO composites were slightly decreased as MgO filler loading increased. However, flexural strength and flexural modulus were improved with increasing filler loading. Notched Izod impact strengths were dramatically lowered by the addition of MgO filler.