• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1421-1426
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• 2014

To improve the inherent safety of the sodium-cooled fast reactor (SFR), the supercritical $CO_2$ ($S-CO_2$) Brayton cycle is being considered as an alternative power conversion system to steam the Rankine cycle. In the $S-CO_2$ system, a PCHE (printed circuit heat exchanger) is being considered. In this type of heat exchangers, diffusion bonding is used for joining the thin plates. In this study, the diffusion bonding characteristics of various austenitic alloys were evaluated. The tensile properties were measured at temperatures starting from the room temperature up to $650^{\circ}C$. For the 316H and 347H types of stainless steel, the tensile ductility was well maintained up to $550^{\circ}C$. However, the Incoloy 800HT showed lower strength and ductility at all temperatures. The microstructure near the bond line was examined to understand the reason for the loss of ductility at high temperatures.

• Applied Chemistry for Engineering
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• v.26 no.3
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• pp.251-258
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• 2015

In the study, PLLA with 12,000 g/mol ($M_n$) and 14,000 g/mol ($M_w$) was synthesized from L-lactide, and used to synthesize PLLA-Br intermediate. PLLA-block-PMMA with 84,000 g/mol ($M_n$) and 126,000 g/mol ($M_w$) was finally synthesized from PLLA-Br intermediate. The glass transition temperature ($T_g$) and initial pyrolysis temperature of PLLA-block-PMMA are $95.5^{\circ}C$ and $289^{\circ}C$, respectively. The PLA film of $50{\pm}3{\mu}m$ thickness was prepared by blending PLA with 9 phr PLLA-block-PMMA followed by stretching biaxially at 3 times under $95^{\circ}C$, and annealing at $120^{\circ}C$ for 2 min. The light transmittance at 550 nm and tensile strength of the film are 88.5% and 44.5 MPa, respectively. To enhance the tensile strength of PLA film, it was required to keep the film more than 2 min at $120^{\circ}C$ during the annealing step after a biaxially orientation.

• Journal of the Korean Institute of Gas
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• v.15 no.2
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• pp.9-14
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• 2011

A set of test was conducted on a SA-372 steel for CNG storage tank to study the effect of hydrogen embrittlement. Tensile tests were carried out several conditions such as CNG, HCNG and H2 gas environment including air and Ar under the 35 MPa. Also, the test speed was set at 4*10^-4/s and 4*10^-5/s respectively. To maintain the high pressure for environmental gas during test process, we chose MTS which was installed autoclave. Test results showed that tensile stress, elongation rate and cross sectional contraction under Ar and CNG charging condition were similar to that of reference of air. And there was little bit change with test speed variations. However, hydrogen added conditions such as HCNG and H2 were revealed noticeable change in elongation rate and cross sectional contraction. Tensile stress was still uniform for all conditions. From the results, the effect of hydrogen embrittlement was confirmed on the hydrogen enriched conditions. Also its effect was showed more strong with much hydrogen concentration and slower test speed.

• Resources Recycling
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• v.24 no.2
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• pp.55-61
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• 2015

In this study, mechanical properties of waste ground rubber tire powder were investigated to evaluate the influence of pre-treatment process for recycling. The tensile test, fracture test and morphology observation were carried out using various kinds of waste ground tire powders, which were produced by grinding and devulcanization process, respectively. As a results, it was found that the produced rubber powder through grinding process increased its tensile strength and elongation with decreasing particle size because of decreasing surface area. Devulcanized rubber powder also increased its tensile strength and elongation by de-crosslink with sulfur. It could be also suggested that devulcanization treatment after grinding process was more efficient recycling process for both increasing tensile property and fracture elongation of waste ground rubber tire powders.

• Journal of the Korean Society of Marine Environment & Safety
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• v.13 no.3
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• pp.223-228
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• 2007

This paper investigated on mechanical characteristic of Al alloy for ship's welded with various welding techniques such as TIG, MIG welding and welding by robot. The yield strength, tensile strength and elongation in TIG welding present 83.9%, 64.6% and 21.9% compare to those in base metal, respectively. The MIG welding is carried out with welding eletrode of ER5183 and ER5356. The mechanical characteristics in ER5356 are improved at approximately 2-4% for ER5183. The mechanical properties of 5083O in welding by robot are better than those of 5456-H116.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.5
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• pp.197-202
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• 2001

The influence of thermal treatment and cold drawing was investigated for poly(ethy1ene terephthalate) films fabricated with various experimental conditions. Samples were elongated at room temperature under stepwise-drawing condition with the cross-head speed kom 0.5 to 500 mrdmin in an universal tester. Stress oscillation was observed in the stress-stnin curve of the samples heat-treatd at 50, 72 and $129^{\circ}C$ for 30 min, but it was not observed in the samples heat-treatd at $83^{\circ}C$ for 30 min. Thermal analyses of the samples were carried out in differential scanning calorimeter at the heating rate df $10^{\circ}C$/min/min, and the glass transition temperature, crystallization peak, enthalpy of fusion and degree of crystallinity were measured. The dynamic mechanical analyses of the samples were also carried out in a multiplefimction internal kiction pendulum at 1 Hz with the heating rate of $1.5^{\circ}C$/min, and it was found that the elastic modulus increases in the order of non-treated, heat-treated, and elongated samples.

• Composites Research
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• v.24 no.4
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• pp.11-16
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• 2011

Retention of interfacial shear strength (IFSS) of polymer composites at cryogenic temperature application is very important. In this work, single carbon tiber reinforced epoxy compositc was used to evaluate IFSS and apparent modulus under room and cryogenic temperatures. The property change of carbon and selected epoxy for particularly cryogenic temperature application were tested in tension and compression. Tensile strength and elongation of carbon fiber decreased at cryogenic temperature, whereas tensile modulus was almost same. On the other hand, epoxy matrix showed the increased tensile strength but decreased elongation. It can be due to maximum thermal contraction existing free volume in cryogenic temperature. IFSS increased up to $-10^{\circ}C$ and then decreased steadily. However, IFSS at cryogenic temperature was still similar to that at room temperature. This result is very useful to cryogenic application since selected epoxy toughness and interfacial adhesion can keep at such low temperature.

• Journal of the Korean Applied Science and Technology
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• v.36 no.4
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• pp.1235-1242
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• 2019

In this study, prepolymer was synthesized through the reaction of isoporon diisocyanate (IPDI) and dimethylolbutanoic acid (DMBA) based on poly (tetramethylene ether) glycol (PTMG) for the synthesis of water-soluble polyurethane to be used as a leather surface coating applied with ethyl acetate and piperazine. Thereafter, the piperazine was chain-extended with 0.01 M, 0.03 M, 0.05 M, and 0.07 M in the water-dispersed resin, and the tensile strength, elongation, CV (cyclic voltammetry), and solvent resistance analysis were performed. Tensile strength of the prepared sample was measured at 5.422 kg_f/㎟ when the piperazine content was 0.07M, and elongation was measured as 587% when the piperazine was 0.01M. Solvent resistance analysis showed the same solvent resistance regardless of piperazine content, and the redox potential was changed according to piperazine content through CV measurement.

• Polymer(Korea)
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• v.35 no.5
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• pp.458-466
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• 2011

In the mixed system of supercritical carbon dioxide/organic solvents, poly(vinyl alcohol)(PVA) film of high degree of hydrolysis could be dyed with a dichroic dye of C. I. direct black 22(DB22) and as a result, high durability was obtained. Especially, as a dye dispersant in a supercritical fluid phase, a mixed solvent system of ethylene glycol: dimethyl sulfoxide=4 : 6 weight ratio was investigated. Then the optimum pressure for dyeing could be reduced down to 200 bar. Using this supercritical fluid system, the maximum dyeing appeared as the transmittance of less than 1% and the waste amount was reduced to the level of 1/10. After 500% drawing of this PVA film, both the polarizing efficiency of 94% and the single piece transmittance of 30% were obtained. The limitation of DB22 and further improvements were also discussed.

• Polymer(Korea)
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• v.37 no.1
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• pp.66-73
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• 2013

Three reactive dichroic dyes with 3,5-dichloro-2,4,6-triazine moiety were synthesized by reaction between dichroic dyes (such as congo red, direct black 22 or direct black 4) and cyanuric chloride. Poly(vinyl alcohol) (PVA) films were dyed with the obtained three reactive dichroic dyes. After 400% drawing of the PVA films, their optical properties were compared with an iodine-doped PVA film prepared in the same condition. Durability test was performed at $50^{\circ}C$ in 85% of relative humidity for 120 hrs. We found that compared with the iodine-doped PVA polarizing film, the relative durability of the PVA polarizing film dyed with the reactive dichroic dyes was greatly improved.