• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.39.1-39.1
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• 2010

겨울철 혹한지방에서의 차량운행 또는 여름철 혹서지방에서의 장시간 차량 운행시 차체를 구성하고 있는 강판에는 약 $-50^{\circ}C{\sim}150^{\circ}C$의 온도환경에 처하게 된다. 따라서 이러한 저온 고온 환경하에서 차체 충돌상품성 예측 및 충돌안전 설계를 위해 온도에 따른 차체 강판의 기계적 물성평가가 요구된다. 이를 위해 본 연구에서는 자동차용 충돌부재에 주로 쓰이는 HS440MPa, HS590MPa급 냉연 고장력 강판에 대해 $-60^{\circ}C{\sim}200^{\circ}C$의 온도범위로 저온 고온 인장시험을 수행 하였다. 각각의 인장시험 결과로부터 온도 별 항복강도, 인장강도, 연신율, 가공경화지수 등 기계적 물성 변화를 평가하였다. 저온 고온 인장시험은 ZWICK Z250 만능재료시험기를 사용하였고 KS5호 규격의 인장시편을 사용하였으며, 시편에 충분한 온도를 가하기 위하여 목표온도 도달 후 20분간 유지한 뒤 인장시험을 수행하였다. 인장시험결과 HS440MPa, HS590MPa급 두 강종 모두 온도가 낮아질수록 강도 및 연신율 등이 증가하였고, 온도가 증가할수록 강도 및 연신율 등 기계적 물성이 저하 되었다. 즉, 우리가 주로 평가해왔던 상온($25^{\circ}C$)에 비해 저온 고온 환경하에서는 강판의 기계적 물성 변화가 큰 것을 알 수 있다. 따라서 혹한 또는 혹서 지방 등 온도차이가 큰 운행환경하에서의 차체 강도 및 충돌안전성 확보를 위해 온도에 따른 강판의 정확한 물성평가가 필요하고 차체 설계시 온도에 따른 강도변화를 충분히 고려하여야 한다.

• Polymer(Korea)
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• v.38 no.2
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• pp.240-249
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• 2014

Multi-walled carbon nanotube (MWNT) reinforced poly(ethylene terephthalate) (PET) composites are studied. To increase the interfacial interactions between PET and MWNTs, the MWNTs are functionalized with bishydroxy-ethylene-terephthalate (BHET). The functionalized MWNTs are melt blended into PET matrix using a twin screw extruder. The amount of MWNTs loaded in PET matrix ranges from 0.5 to 2.0 wt%. After compounding and spinning, the filaments are post-drawn and annealed. To verify the chemical modifications of carbon nanotubes, Raman, $^1H$ NMR, XPS, TGA and FE-SEM are used. The nanocomposites are also analyzed with DSC, TGA, and UTM. These tests show that crystallization temperature and thermal degradation temperature increase due to the functionalized MWNTs. Also, tensile test shows that yield strength and toughness increase more than 30% with addition of only 1 wt% of MWNTs. These results show that the introduction of BHET onto the MWNTs is a very effective way in manufacturing MWNT/PET composite.

• Journal of Conservation Science
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• v.25 no.2
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• pp.197-206
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• 2009

Natural preservative agents are generally made of antibiotic substances that are extracted from plants. They are used mainly to keep in an original good state food, natural cosmetic goods and medicines which are likely to get rotten. The purpose of this study is to investigate whether natural preservative agents can be applied to fabrics for the preservation of textile cultural properties. For the purpose, this researcher experimented with a certain natural preservative agent which was developed to preserve natural cosmetic goods. The study found that when treated with the foresaid natural preservative agent whose ratio to water was 1%, fabrics showed little changes in color and tensile strength, almost neutral pH, high antibiosis and anti-fungus and high resistance to Bacillus cereus that is much detrimental to silk fabrics. As a part of the study, a preliminary test on the possibility of using natural preservative agents to preserve textile cultural properties, found that when kept covered up with the 1% natural preservative agent-treated fabrics for 72 hours, excavated textile relics showed a dramatic decrease in microbial growth.

• Journal of Power System Engineering
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• v.9 no.4
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• pp.96-101
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• 2005

Magnesium alloys have been widely used for many structural components of automobiles and aircraft because of high specific strength and good cast ability in spite of hexagonal closed-packed crystal structure of pure magnesium. In this study, uniaxial tension tests at high temperature and creep tests are done in order to investigate the characteristics of high temperature and mechanisms for creep deformation of AZ31 Mg alloy. Yield stress and ultimate tensile stress decreased with increasing temperature, but elongation increased from results of uniaxial tension test at high temperature. The apparent activation energy Qc, the applied stress exponent n and rupture life have been determined during creep of AZ31 Mg alloy over the temperature range of 473K to 573K and stress range of 23.42 MPa to 93.59 MPa, respectively, in order to investigate the creep behavior. Constant load creep tests were carried out in the equipment including automatic temperature controller, whose data are sent to computer. At around the temperature of $473K{\sim}493K$ and under the stress level of $62.43{\sim}93.59%MPa$, and again at around the temperature of $553K{\sim}573K$ and under the stress level of $23.42{\sim}39.00MPa$, the creep behavior obeyed a simple power-law relating steady state creep rate to applied stress and the activation energy for the creep deformation was nearly equal, respectively, and a little low to that of the self diffusion of Mg alloy including aluminum. Also rupture surfaces at high temperature have had bigger dimples than those at lower temperature by SEM.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.15 no.3
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• pp.166-175
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• 2005

Health effects associated with metal working fluid (MWF) exposures include dermatitis, respiratory disease, hypersensitive pneumonitis, and asthma. Frequently, occupational exposures to MWFs are controlled by ventilating an enclosure with an air cleaning unit that includes a fan preceded by various kinds of filtration. There are several kinds of air cleaning units used in machining centers. But the associated troubles have hindered from efficiently using these devices. The main problem is the relatively short period of filter replacement. The reason is that the air cleaning units usually do not have the de-oiling systems, thus leading the earlier clogging of filters and reducing the flow rate of hood. Thus, the first stage of study was conducted to overcome this problem by developing the new oil mist collector equipped with the easy de-oiling system. The principle of de-oiling is that the centrifugal force generated by spinning the drum covered by filter fabric separates oils from the filter fabric. It would be very similar to the spin-dry laundry. By adopting this de-oiling technique, the problems associated with the conventional oil mist collectors could be solved. Several tests/analyses were performed to make the lab-scale oil mist collector. The collection efficiencies and the de-oiling efficiencies of commercially available filter fabrics were tested. Subsequently, the endurance test were conducted by observing SEM photos of filter fabrics and measuring tensile strength/expansion coefficient after spinning the filter drum for 20 minutes at the different rotation speeds. By doing these experiments, the most appropriate filter fabric and rotation speed/duration were selected. Finally, the new oil mist collector was designed. In the near future, this device must be tested in the real machining center.

• International Journal of Highway Engineering
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• v.7 no.3 s.25
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• pp.71-78
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• 2005

This study focuses on finding out engineering characteristics of asphalt concrete mixtures using mineral fillers with recycled waste lime, which is a by-product in the Soda Ash(Na2CO3) production course. The materials tested in this study were made with 25%, 50%, 75% and 100% of mixing ratio based on the conventional mineral filler ratio to analyze the recycle possibility of the waste lime. The asphalt concrete mixtures with recycled waste lime and hydrated lime, and conventional asphalt concrete mixtures were evaluated through their fundamental engineering properties such as Marshall stability, indirect tensile strength, resilient modulus, permanent deformation characteristics, moisture susceptibility and fatigue resistance. The results indicate that the application of recycled waste lime as mineral filler improves the permanent deformation characteristics, stiffness and fatigue endurance of asphalt concrete mixtures at the wide range of temperatures. It is also found that the mixtures with recycled waste lime show higher resistance against stripping than conventional asphalt concrete mixtures. It is concluded from various test results that the waste lime can be used as mineral fillers and especially can greatly improve resistance to permanent deformation of asphalt concrete mixtures at high temperatures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.59-67
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• 2014

In tension lap splices of straight deformed bars, KCI Code (KCI2012) and ACI Code (ACI318-11) requires that the lap lengths for class B splice are 1.3 times as development length. KCI2012 contains development length provisions for the use of headed deformed bars in tension and does not allow their tension lap splices. The purpose of this experimental study is to evaluate that KCI2012 equation for the development length, $l_{dt}$, of headed bars can be used to calculate the lap length, $l_s$, of headed deformed bars in grade SD400 and SD500, having specified yield strength of 400 and 500 MPa. Test results showed that specimens with $l_s$ equal to $1.3l_{dt}$ had maximum flexural strengths as 1.16~1.31 times as the nominal flexural strengths, flexural failure mode, and ductility. These observations indicate that $1.3l_{dt}$ is suitable to the tensile lap length of headed deformed bars in grade SD400 and SD500.

• Journal of the Korean Society for Heat Treatment
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• v.27 no.6
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• pp.281-287
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• 2014

Microstructural and mechanical characteristics of Al-6Si-2Cu alloy for engine mount bracket prepared by gravity casting (as-cast) and die-casting (as-diecast) process have been investigated. For the microstructural characterization, the inductively coupled plasma mass spectrometry (ICP-MS), optical microscope (OM), scanning electron microscope (SEM) and electron probe microanalysis (EPMA) analyses are conducted. For the intermetallic phases, the X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) are also conducted with quantitative and qualitative analysis. Micro Vickers hardness and static tensile test are achieved in order to measure mechanical properties of alloys. Secondary dendrite arm spacing (SDAS) of as-cast and as-diecast show 37um and 18um, respectively. A large amount of coarsen eutectic Si, $Al_2Cu$ intermetallic phase and Fe-rich phases are identified in the Al-6Si-2Cu alloy. Mechanical properties of gravity casting alloy are much higher than those of die-casting alloy. Especially, yield strength and elongation of gravity casting alloy show 2 times higher than die-casting alloy. After shot peening, shot peening refined the surface grains and Si particles of the alloys by plastic deformation. The surface hardness value shows that shot peening alloy has higher value than unpeening alloy.

• Korean Chemical Engineering Research
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• v.50 no.1
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• pp.6-10
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• 2012

The main objective of this work was studying the influence of paraffin oil(PO) on the adhesion properties at low temperature in styrene-butadiene-styrene(SBS) copolymer and crumb rubber(CR) modified asphalt. The temperature susceptibility of SBS/CR asphalt and PO/SBS/CR/asphalt blends were measured by penetration and softening point. Adhesion properties at low temperature and dispersion of modifiers in PO/SBS/CR/asphalt blends were evaluated by universal test machine and florescence microscopy, respectively. The adhesion properties of PO/SBS/CR/asphalt blends at low temperature increased in the proportion of SBS contents with both 5 and 10 wt % of paraffin oil. Results showed that the maximum tensile adhesion strength and toughness energy at $-20^{\circ}C$ were obtained when PO and SBS contents were 10 wt % and 6 wt %, respectively. The addition of PO is effective for enhancing the flexibility of SBS/CR/asphalt blends and leads to the increase of toughness at low temperature.

• Korean Journal of Materials Research
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• v.18 no.6
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• pp.326-333
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• 2008

Since the 1990s, the second generation of Zirconium alloys containing main alloy compositions of Nb, Sn and Fe have been used as a replacement of Zircaloy-4 (Zr-Sn-Fe-Cr), a first-generation Zirconium alloy, to meet severe and rigorous reactor operating conditions characterized by high-burn-up, high-power and high-pH operations. In this study, the mechanical properties and creep behaviors of Zr-Sn-Fe-Cr and Zr-Nb-Sn-Fe alloys were investigated in a temperature range of $450{\sim}500^{\circ}C$ and in a stress range of $80{\sim}150\;MPa$. The mechanical testing results indicate that the yield and tensile strengths of the Zr-Nb-Sn-Fe alloy are slightly higher compared to those of Zr-Sn-Fe-Cr. This can be explained by the second phase strengthening of the $\beta$-Nb precipitates. The creep test results indicate that the stress exponent for the steady-state creep rate decreases with the increase in the applied stress. However, the stress exponent of the Zr-Sn-Fe-Cr alloy is lower than that of the Zr-Nb-Sn-Fe alloy in a relatively high stress range, whereas the creep activation energy of the former is slightly higher than that of the latter. This can be explained by the dynamic deformation aging effect caused by the interaction of dislocations with Sn substitutional atoms. A higher Sn content leads to a lower stress exponent value and higher creep activation energy.