• Journal of the Korea Concrete Institute
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• v.24 no.5
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• pp.525-533
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• 2012

In this study, bending tests were performed on beam specimens made of UHPCC with the fiber content range of 0~5 vol% to investigate the contribution of fiber content to first cracking strength and flexural tensile strength. Also, four-point bending tests for unnotched beam as well as three-point bending test for notched beam were performed to estimate the effect of the presence of notch on the strengths. The experiment result showed that the increase in fiber content made linear improvement in the flexural tensile strength; whereas first cracking strength was enhanced only when at least 1 vol% of fibers was incorporated. Comparison of the bending test results with and without notch showed that the notch effect varied with the fiber content. The increase in fiber content diminished the effect of stress concentration on the notch tip, reducing the difference in the strengths. With much higher fiber content, the effect of stress concentration almost disappeared and the defection on cracking plane or the size effect dominated the strengths, consequently resulting in higher strengths in the notched beams than the unnotched ones.

• Journal of the Korea Concrete Institute
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• v.25 no.5
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• pp.547-554
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• 2013

This study was intended to estimate the bond strength of steel fiber in UHPFRC through pullout test. The pullout test was carried out with the double-sided pullout specimens with multiple fibers. First, the effect of fiber density on the bond strength was investigated, and the experimental result presented that the density range considered in this study was proved not to produce fiber-to-fiber interaction. The bond strength was estimated from several methods, which are based on the pullout load or energy at peak load, and the total energy absorbed until fibers are pulled out completely. the estimated bond strength obtained from the total energy was shown to be under the influence of the embedded length of fiber. the bond strengths obtained from peak load condition was 6.64 MPa in average, which had little difference compared to 6.46 MPa calculated by peak load only. Considering simplicity of test and analysis, it may be no matter to estimate the bond strength from peak load in pullout test.

• Journal of the Korea Institute of Building Construction
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• v.8 no.3
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• pp.93-99
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• 2008

The purpose of this study is to evaluate the bond strength and corrosion resistance of coated reinforcing bar using hybrid-type polymer cement slurry(PCS). PCS coated steels, which is made from two types of polymer dispersions such as St/BA and EVA are prepared, and tested for bond strength and various corrosion resistances such as autoclaved cure, carbonation and H2SO4 solution. From the test results, the bond strength of PCS coated reinforcing bar using ordinary portland cement at 1-5, 2-1 and 4-5 of mixes is higher than that of uncoated regular steel. However, bond strength of almost PCS coated reinforcing bars using ultra rapid high strength cement is higher than that of epoxy coated bar, is also in ranges of 102% to 123% compared to that of uncoated regular steel. In autoclaved accelerating test, the ratio of corrosion of uncoated regular steel is increased with the increase in NaCl content, but the corrosion of PCS coated steel was very small. In the acceleration test for carbonation, increasing the amount of NaCl the corrosion of coated steel did not produce. The corrosion of uncoated regular steel is increased with the increase in the amount of NaCl. It can be seen that the NaCl following the acceleration test for carbonation can lower the corrosion resistance of concrete. As a result, the corrosion of steel largely is affected by the acceleration curing, chloride ion penetration and carbonation and shown more severe corrosion by applying complex factors. These corrosions of steel can be suppressed by the coating of PCS.

• Journal of the Korean Ceramic Society
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• v.15 no.2
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• pp.89-97
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• 1978

The basic mechanism of adherence in sintered high purity alumina ceramic-to-metal bonding was studied. Emphasis was placed on flux composition, porosity of the fired ceramics, and metallizing mixtures. The study was conducted on 95 and 99.5% alumina, using molydbenum-manganese, molybdenum-manganese-silicon dioxide metallizing compositions. Metallizing was performed in wet hydrogen (dew point, ＋17$^{\circ}C$) at 145$0^{\circ}C$ for 45min. This experiment indicated that adhernece mechanism of ultra high purity alumina ceramic was attributed to formation of $MnAl_2O_$4, and in the case of 95% alumina containing glass, the migration of glass from the interface into the void of the metal coating was the main role to the adhrence. It showed also that greater the bond-strength was resulted as porosity was increased.

• Transactions of Materials Processing
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• v.23 no.6
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• pp.380-385
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• 2014

An analysis procedure is proposed to improve the prediction accuracy of springback as well as to evaluate the structural stability of the tooling used for fabricating a side sill part from UHSS. The analysis couples the stamping analysis and the subsequent analysis of the tool structural. The deformation and stress results for the tool structure are obtained from the proposed analysis procedure. The results show that the amount of deformation and stresses are so high that the tool structure must be reinforced and the tooling design must consider structural stability. Springback is predicted with CAE in order to compare the prediction accuracy between the given tool geometry and the geometry from the structural analysis. The simulation results with the deformed tool can predict the experimental springback tendency accurately.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.537-542
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• 2004

Machinble Ceramics have some excellent properties as the material for the mechanical components. It is, however, very difficult to grind ceramics with high efficiency because of their high strength, hardness and brittleness. Lapping used diamond slurry and lapping by in-process electrolytic dressing is developed to solve this problem. On this paper, a comparative study of processing ability of lapping used diamond slurry and lapping by in-process electrolytic dressing.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1999.06a
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• pp.403-418
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• 1999

Fiber growth of Al2O3/R-Al-O(R=Y, Gd, Dy, Ho, Er) eutectic by the micro-pulling down methods is described. The thermal stability and strength at elevated temperature of each material is evaluated in relation to the microstructure. PACS: 81.05 Mh, 81.10 Fq, 81.30-t.

• Composites Research
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• v.29 no.4
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• pp.186-193
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• 2016

The development of electrospun nanofibers with improved mechanical properties is of great scientific and technological interest because of their wide-range of applications. Reinforcement of carbon nanotubes (CNTs) into the polymer matrix is considered as a promising strategy for substantially enhancing the mechanical properties of resulting CNTs/polymer composite mats on account of extraordinary mechanical properties of CNTs such as ultra-high Young's modulus and tensile strengths. This paper summarizes the recent developments on electrospun CNTs/polymer composite mats with an emphasis on their mechanical properties.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.531-536
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• 2003

Equal channel angular pressing (ECAP) has been employed to produce materials with ultra-fine grains that have high strength and high corrosion resistance properties. In order to obtain super plastic deformation during ECAP, multipass angular pressing is frequently employed. In this paper, three-dimensional finite element analyses have been performed to investigate the deformation behavior of pure-Zr specimen and the effects of process parameters for equal channel multi-angular pressing (ECMAP) process. The results have been compared with some experimental results

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.620-624
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• 1997

Corrugated membranes which are used as a means of liquid- and gas-sealing for a LNG storage tank and provide one of the most reliable primary barrier are the main component of in-ground membrane types for the assurance of high safety. It absorbs large thermal and mechanical deformations caused by ultra low temperature of LNG, -162 .deg.c, the cryogenic liquid and mechanical deformations caused by was carried out on crossing corrugation by commercial F.E code, ANSYS. This paper presents some of results in stress analysis of membranes performed for the purpose to investigate the strength of existing membrane for LNG storage tank designed by IHI,MHI, KHI and KGC expect for Technigaz eariy published. Based on these analytical studies,design criteria were estabilished and SHI original membranes having a high level of safety and fitting to larger capacities were developed.