• 대한기계학회논문집A
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• 제37권2호
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• pp.199-204
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• 2013

최근 차량 경량화를 통한 에너지 절감을 위해서 무거운 철강재료를 경금속이나 복합재료로 대체하는 연구가 많이 진행되고 있다. 이중, 폴리머 기반의 복합재료는 사출성형을 통해서 복잡한 형상의 제작이 가능하고, 유리섬유나 탄소섬유를 함께 사용하여 철강재료 수준으로 기계적 물성을 높일 수 있는 장점이 있다. 하지만 엔진의 고온과 우기에서의 높은 습도 환경은 폴리머의 기계적 물성을 낮추기 때문에 재료선택 과정에서 반드시 고려해야 한다. 본 연구에서는 사출성형을 통해 만들어진 유리섬유강화플라스틱을 엔진룸 내부 온도와 유사한 $85^{\circ}C$ 환경과 우기시의 최대 수분흡수 환경하에서의 기계적 물성변화를 인장시험을 통해 알아보았다. 그 결과, 고온환경에서 최대인장강도가 약 23% 감소를 보였고, 수분에 의해서는 약 30% 감소하였으며, 고온과 수분 모두에 대해서는 약 70% 감소를 확인하였으며 이는 재료 선정시 반드시 고려해야 할 영향으로 판단되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.122-122
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• 1999

Graphite with its advantages of high thermal conductivity, low thermal expansion coefficient, and low elasticity, has been widely used as a structural material for high temperature. However, graphite can easily react with oxygen at even low temperature as 40$0^{\circ}C$, resulting in CO2 formation. In order to apply the graphite to high temperature structural material, therefore, it is necessary to improve its oxidation resistive property. Silicon Carbide (SiC) is a semiconductor material for high-temperature, radiation-resistant, and high power/high frequency electronic devices due to its excellent properties. Conventional chemical vapor deposited SiC films has also been widely used as a coating materials for structural applications because of its outstanding properties such as high thermal conductivity, high microhardness, good chemical resistant for oxidation. Therefore, SiC with similar thermal expansion coefficient as graphite is recently considered to be a g행 candidate material for protective coating operating at high temperature, corrosive, and high-wear environments. Due to large lattice mismatch (~50%), however, it was very difficult to grow thick SiC layer on graphite surface. In theis study, we have deposited thick SiC thin films on graphite substrates at temperature range of 700-85$0^{\circ}C$ using single molecular precursors by both thermal MOCVD and PEMOCVD methods for oxidation protection wear and tribological coating . Two organosilicon compounds such as diethylmethylsilane (EDMS), (Et)2SiH(CH3), and hexamethyldisilane (HMDS),(CH3)Si-Si(CH3)3, were utilized as single source precursors, and hydrogen and Ar were used as a bubbler and carrier gas. Polycrystalline cubic SiC protective layers in [110] direction were successfully grown on graphite substrates at temperature as low as 80$0^{\circ}C$ from HMDS by PEMOCVD. In the case of thermal MOCVD, on the other hand, only amorphous SiC layers were obtained with either HMDS or DMS at 85$0^{\circ}C$. We compared the difference of crystal quality and physical properties of the PEMOCVD was highly effective process in improving the characteristics of the a SiC protective layers grown by thermal MOCVD and PEMOCVD method and confirmed that PEMOCVD was highly effective process in improving the characteristics of the SiC layer properties compared to those grown by thermal MOCVD. The as-grown samples were characterized in situ with OES and RGA and ex situ with XRD, XPS, and SEM. The mechanical and oxidation-resistant properties have been checked. The optimum SiC film was obtained at 85$0^{\circ}C$ and RF power of 200W. The maximum deposition rate and microhardness are 2$mu extrm{m}$/h and 4,336kg/mm2 Hv, respectively. The hardness was strongly influenced with the stoichiometry of SiC protective layers.

• 한국화재소방학회논문지
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• 제2권1호
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• pp.3-10
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• 1988

Concrete is incombustible and has good fire resisting properties, i. e. when exposed to fire it continues to perform satisfactorily for a reasonable period of time. Nevertheless, with time and high temperature gradient, brought about the fire, causes cracking and spatting. Further deterioration and loss of strength are caused by gradual dehydration of concrete paste. This paper is aimed to make a proposal for the design and construction of reinforced concrete structures with more sufficent resistance to fire by the theoritical analysis, which is base4 on investigation of general damages by the fire and change of properties on concrete influenced by high temperature.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1998년도 특별강연 및 추계학술발표 개요집
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• pp.11-24
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• 1998

The invention of fusion wilding technology has brought on a revolutionary change in manufacturing industry which enables the construction of large scale high temperature plants in chemical, petrochemical and power generation industries. However, among the failure cases of high temperature components, premature failures of weldments have taken a large percentage that indicates the detrimental effect of welding on structural integrity. The accurate prediction of the high temperature behaviour of welded components is thus becoming increasingly important in order to realise an optimised design and maintenance of a plant life. In the present paper, recent research activities on high temperature behaviour of welded structures are briefly summarised. A local deformation measuring technique is proposed to determine the creep properties of weldment constituents. A damage mechanics approach is introduced to study the life reduction and ductility reduction due to the presence of a weld in high temperature structures. Finally, the high temperature creep crack growth in weldments is discussed.

• Journal of Welding and Joining
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• 제26권5호
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• pp.60-65
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• 2008

Ferritic stainless steels of the 400 series have been available for automotive exhaust system, heat exchanger, radiater etc. in various industrial because heat resistance, corrosion resistance and strength are excellent. Especially, automotive exhaust system is required good heat resistance because typical temperature of exhaust system exposed during operation of engine is reach up to $800^{\circ}C$. However, research for effect of high temperature in ferritic stainless steels is not enough. In this study, high temperature tensile properties of lap weld of ferritic stainless steels(STS 429) were investigated. In accordance with heat input, lap welds had been produced and were evaluated at high temperature($800^{\circ}C$) to compare high temperature tensile properties. In addition, room temperature tensile tests were carried out for non-aging and aging specimens. As a result of R.T tensile test, non-aging specimens were fractured in base metal except for low heat input specimen and aging specimens were fractured in weld metal. Also high temperature tensile test were carried out by aging specimen. After high temperature tensile test, fracture of aged specimen was occurred in base metal except for low heat input specimen. Fracture surface of low heat input specimen in weld metal was confirmed as brittle fracture with observation using scanning electron microscope(SEM). Significant decrease in ultimate tensile strength (between 82 and 85%) was observed for aged ferritic stainless steels(STS 429) when tested at high temperature.

• 콘크리트학회논문집
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• 제23권3호
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• pp.321-330
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• 2011

최근, 고강도 콘크리트의 잔존 역학적 특성에 관한 섬유의 혼입과 고온의 영향은 실험적으로 연구되어지고 있다. 이 논문에서는 고온에 노출된 물시멘트비 55%, 42% 및 35%에 따른 콘크리트의 잔존 역학적 특성을 0.05~0.20 vol.%의 범위로 폴리프로필렌 섬유를 혼입한 콘크리트와 비교하여 평가하였고, 고려된 요인은 섬유 혼입량, 콘크리트 강도 및 재하 하중량이다. 폭렬 발생 시간, 열팽창 변형, 길이 변화 및 중량 감소의 측정과 압축강도, 탄성계수 및 에너지 흡수 능력의 평가를 실시했다. 결과로서는 고온에 노출된 50 MPa급 콘크리트의 폭렬을 방지하기 위해서 0.05 vol.% 이상의 PP섬유가 필요했다. 또한, PP섬유의 단면적은 고온에 노출된 섬유보강 콘크리트의 폭렬 경향과 잔존 역학적 특성에 관해서 영향을 미치는 것으로 나타났다. 특히, 외부 하중은 콘크리트의 잔존 역학적 특성 뿐만 아니라 폭렬의 위험 및 취성적 경향을 증가시켰다.

• 한국분말재료학회지
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• 제27권1호
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• pp.8-13
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• 2020

In this study, we investigated the effects of precipitates and oxide dispersoids on the high-temperature mechanical properties of oxide dispersion-strengthened (ODS) Ni-based super alloys. Two ODS Ni-based super alloy rods with different chemical compositions were fabricated by high-energy milling and hot extrusion process at 1150 ℃ to investigate the effects of precipitates on high-temperature mechanical properties. Further, the MA6000N alloy is an improvement over the commercial MA6000 alloy, and the KS6000 alloy has the same chemical composition as the MA6000 alloy. The phase and microstructure of Ni-based super alloys were investigated by X-ray diffraction and scanning electron microscopy. It was found that MC carbide precipitates and oxide dispersoids in the ODS Ni-based super alloys developed in this study may effectively improve high-temperature hardness and creep resistance.

• 한국안전학회지
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• 제37권4호
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• pp.11-19
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• 2022

This paper presents the effects of high temperature and water absorption on the mechanical behaviors of carbon-aramid fiber composites, specifically their strength, elastic modulus, and fracture. These composites are used in industrial structures because of their high specific strength and toughness. Carbon fiber composites are vulnerable to the impact force of external objects despite their excellent properties. Aramid fibers have high elongation and impact absorption capabilities. Accordingly, a hybrid composite with the complementary properties and capabilities of carbon and aramid fibers is fabricated. However, the exposure of aramid fiber to water or heat typically deteriorates its mechanical properties. In view of this, tensile and flexural tests were conducted on a twill woven carbon-aramid fiber hybrid composite to investigate the effects of high temperature and water absorption. Moreover, a multiscale analysis of the stress behavior of the composite's microstructure was implemented. The results show that the elastic modulus of composites subjected to high temperature and water absorption treatments decreased by approximately 22% and 34%, respectively, compared with that of the composite under normal conditions. The crack behavior of the composites was well identified under the specimen conditions.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.146-151
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• 2003

Reduced Activation Ferritic/Martenstic (RAFs) are leading candidates for structural materials of D-T fusion reactor. One of The RAFs, JLF-1 (9Cr-2W-V, Ta) has been developed and proved to have good resistance against high-fluency neutrino irradiation and good phase stability. Recently, in order to clarify the strengthening mechanical at high temperature, a new scheme to improve high temperature mechanical properties is desired. Therefore, the creep properties and creep life prediction by Larson-Miller Parameter method for JLF-1 to be used for fusion reactor materials or other high temperature components were presented at the elevated temperatures of $500^{\circ}C$, $550^{\circ}C$, $600^{\circ}C$, $650^{\circ}C$ and $704^{\circ}C$. It was confirmed experimentally and quantitatively that a creep life predictive e벼ation at such various high temperatures was well derived by LMP.

• 열처리공학회지
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• 제13권6호
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• pp.405-411
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• 2000

The effects of added elements, such as Co or Nb, on wear properties of high speed steel by powder metaliurgy(PM-HSS) had been eluminated in auther's previous paper. In addition, it is generally known that the wear properties of materials have been influenced by heat-treating conditions as well. Therefore, a study has been done to clarify the effects of heat-treating conditions on wear properties of PM-HSS. The wear tests have been performed under the same conditions as the previous paper using heat-treated PM-HSS(5%Co-1%Nb) with different quenching and tempering temperatures. The result of this paper shows that wear resistance of PM-HSS is improved with relatively high quenching temperature. However, tempering temperature is not sensitive to the wear resistance in the range of high quenching temperature. It may be deduced by the fact that the shear strength of matrix by strengthening mechanisms due to not only the quenching aging but also dispersion-hardening is improved.