• Journal of Advanced Marine Engineering and Technology
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• 제39권4호
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• pp.425-431
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• 2015

선박의 LNG(liquefied natural gas) 연료 공급 시스템에서 천연가스는 $50^{\circ}C$의 온도와 35MPa의 압력을 가진 가스 상태로 기화기에서 엔진으로 이송되므로, 이러한 열 하중을 고려한 구조 안전성 평가가 반드시 필요하다. 본 연구에서는 먼저 재료에 미치는 열의 영향을 분석하기 위하여 이중 배관의 재료인 슈퍼 듀플렉스 스테인리스강의 어닐링 시간을 고려한 일축 인장 실험을 수행하였다. 또한 구조 안전성 평가를 위해, 현재 널리 사용되는 고정식 지지대를 가지는 고온-고압 이중 배관에 대한 열-구조 해석을 수행하였다. 지지대와 내관 사이의 응력 집중을 최소화하기 위하여, 내관을 따라 미끄러질 수 있는 슬라이딩 지지대의 새 형상들을 제안하였고, 열-구조 해석 결과를 통해 최적의 지지대를 제안하였다. 마지막으로 제안된 지지대를 사용한 전체 이중배관에 대한 해석을 통해 안전성을 평가하였다. 본 연구의 결과는 차후 LNG 연료 공급 시스템의 고온-고압 이중 배관 설계 시 참고자료로서 활용될 수 있으며, 이중 배관의 슬라이딩 지지대를 설계함에 있어서 그 활용가치가 있다고 판단된다.

• 한국터널지하공간학회 논문집
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• 제15권1호
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• pp.1-11
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• 2013

강섬유 보강콘크리트는 NATM 터널의 숏크리트와 세그먼트 등 라이닝에 주로 적용된다. 터널화재시 라이닝은 화재에 직접적으로 노출되기 때문에 고온노출시 SFRC의 성능변화는 매우 중요하다. 본 연구에서는 고온에 노출된 강섬유보강콘크리트의 인장성능을 DPT 실험을 통하여 검토하였다. 고온 노출온도, 강섬유 혼입률 및 종류가 파괴형태, DPT 인장강도, 실험의 변동계수에 미치는 영향을 분석하였다. 실험결과, 강섬유 보강으로 인한 잔존인장강도의 증가를 확인하였으며, 혼입률이 증가할수록 효과적임을 확인하였다. 그러나, DPT 인장강도는 고온노출로 인한 파괴면의 변화를 고려할 수 없기 때문에 파괴에너지의 고찰이 필요한 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2139-2146
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• 2023

During reactor operation, the divertor must withstand unprecedented simultaneous high heat fluxes and high-energy neutron irradiation. The extremely severe service environment of the divertor imposes a huge challenge to the bonding quality of divertor joints, i.e., the joints must withstand thermal, mechanical and neutron loads, as well as cyclic mode of operation. In this paper, potassium-doped tungsten (KW) is selected as the plasma facing material (PFM), oxygen-free copper (OFC) as the interlayer, oxide dispersion strengthened copper (ODS-Cu) alloy as the heat sink material, and reduced activation ferritic/martensitic (RAFM) steel as the structural material. In this study, a vacuum brazing technology is proposed and optimized to bond Cu and ODS-Cu alloy with the silver-free brazing material CuSnTi. The most appropriate brazing parameters are a brazing temperature of 940 ℃ and a holding time of 15 min. High-quality bonding interfaces have been successfully obtained by vacuum brazing technology, and the average shear strength of the as-obtained KW/Cu and ODS-Cu alloy joints is ~268 MPa. And a fabrication route for manufacturing the flat-type divertor target based on brazing technology is set. For evaluating the reliability of the fabrication technologies under the reactor relevant condition, the high heat flux test at 20 MW/m² for the as-manufactured flat-type KW/Cu/ODS-Cu/RAFM mockup is carried out by using the Electron-beam Material testing Scenario (EMS-60) with water cooling. This paper reports the improved vacuum brazing technology to connect Cu to ODS-Cu alloy and summarizes the production route, high heat flux (HHF) test, the pre and post non-destructive examination, and the surface results of the flat-type KW/Cu/ODS-Cu/RAFM mockup after the HHF test. The test results demonstrate that the mockup manufactured according to the fabrication route still have structural and interfacial integrity under cyclic high heat loads.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 추계학술대회 논문집
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• pp.248-253
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• 1998

Recently, the uses of Ceramic/metal bonded joints, resin/metal joints, adhesive joints, composite materials which are composed of dissimiliar materials have increased in various industry fields. Since the ceramic/metal bonded joints material is made at a high temperature, residual stress distributions due to differences in material properties were investigated by varying material parameters. The two dimensional finite element analysis was performed to study residual stress distribution in Si3N4/SM45C bonded joint with a copper interlayer between the silicon nitride(Si3N4) and the structural carbon steel(SM45C) and 4-point bending tests were carried out under room temperature. Fracture surface and crack propagation path were observed using scanning electron microscope and characteristics of its fracture was discussed.

• 한국화재소방학회논문지
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• 제26권6호
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• pp.45-50
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• 2012

폭렬은 철근노출과 함께 구조부재의 단면을 감소시키며, 이로 인하여 구조적 거동에 심각한 문제를 발생시킨다. 고강도 콘크리트에 내화 모르터를 피복함으로서 화재시 폭렬을 방지할 수 있으며, 콘크리트 내의 철근의 온도상승을 지연시킬 수 있다. 본 연구의 목적은 이러한 고강도 콘크리트의 내화피복재로 활용하기 위한 것으로 퍼라이트와 폴리프로필렌 섬유로 경량 모르터를 제조하여 온도이력 성상을 파악하는데 있다. 이에 따른 실험인자로는 폴리프로필렌 섬유의 첨가량과 길이이다. 연구결과 폴리프로필렌 섬유를 첨가함으로서 모르터의 공극구조를 변화시킬 수 있었으며, 이는 내부 온도상승을 지연시킨다. 또한 고강도 콘크리트의 내화피복재로서 경량 모르터를 사용할 수 있는 가능성을 확인하였다.

• 한국안전학회지
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• 제30권1호
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• pp.21-27
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• 2015

In this study, interfacial characteristics between SOFC and Ag paste as current collector was estimated in the high temperature environment. The Ag paste was used to connect the unit cell of SOFC strongly with interconnector and provide the electrical conductivity between them. To confirm electrical conductivity, Ag paste was treated in the furnace at $800^{\circ}C$ for 48 hours. The sheet resistance of Ag paste was measured to compare the resistance values before and after the heat treatment. Also, the four-point bending test was performed to measure the interfacial adhesion. The unit cell of SOFC and $SiO_2$ wafer were diced and then attached by Ag paste. The $SiO_2$ wafer had the center notch to initiate a crack from the tip of the notch. The modified stereomicroscope combined with the CCD camera and system for measuring the length was used to observe the fracture behavior. To compare the characteristics before heat treatment and after heat treatment, the specimen was exposed in the furnace at $800^{\circ}C$ for 48 hours and then the interfacial adhesion was evaluated. Finally, the interfacial adhesion energy quantitatively increases $1.78{\pm}0.07J/m^2$ to $4.9{\pm}0.87J/m^2$ between the cathode and Ag paste and also increase $2.9{\pm}0.47J/m^2$ to $5.12{\pm}1.01J/m^2$ between the anode and Ag paste through the high temperature. Therefore, it is expected that Ag paste as current collector was appropriate for improving the structural stability in the stacked SOFC system if the electrical conductivity was more increased.

• 한국분말재료학회지
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• 제24권1호
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• pp.53-57
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• 2017

In this study, we report the microstructure and the high-temperature oxidation behavior of Fe-Ni alloys by spark plasma sintering. Structural characterization is performed by scanning electron microscopy and X-ray diffraction. The oxidation behavior of Fe-Ni alloys is studied by means of a high-temperature oxidation test at $1000^{\circ}C$ in air. The effect of Ni content of Fe-Ni alloys on the microstructure and on the oxidation characteristics is investigated in detail. In the case of Fe-2Ni and Fe-5Ni alloys, the microstructure is a ferrite (${\alpha}$) phase with body centered cubic (BCC) structure, and the microstructure of Fe-10Ni and Fe-20Ni alloys is considered to be a massive martensite (${\alpha}^{\prime}$) phase with the same BCC structure as that of the ferrite phase. As the Ni content increases, the micro-Vickers hardness of the alloys also increases. It can also be seen that the oxidation resistance is improved by decreasing the thickness of the oxide film.

• 한국건축시공학회지
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• 제18권6호
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• pp.569-576
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• 2018

현대사회에서 건축물은 대다수가 RC구조로 건설되어지고 있다. RC구조의 건축물은 시공상의 하자발생, 설계단계에서의 오차발생 등과 같은 인위적인 요인과 지진, 태풍 등의 자연적인 요인에 의해 구조적 불안정성이 발생하고 이를 해결하기 위해 다수의 보수보강공법이 이루어지고 있다. 보강공법 중 FRP 보강공법에서 사용하는 유기계 에폭시 접착제는 고온에 노출되었을 때 부착파괴가 급격하게 발생하게 되며 이는 보강재의 탈락으로 직결된다. 따라서 본 연구에서는 고온에 노출되었을 때 FRP 보강재에 전달되는 열을 감소시켜주며 일정수준 이상의 부착성능을 가진 무기계 내화 모르타르의 개발을 목적으로 실험을 진행하였다. 실험 결과 EVA수지의 포함으로 상온조건에서 높은 부착강도를 나타내었으며, 가열조건에서도 약 $300^{\circ}C$까지 전혀 성능저하를 나타내지 않았다. 또한, 이면온도는 두께가 증가할수록 낮았으며, 가열 2시간 이후에에서는 약 $780^{\circ}C$의 일정한 온도로 수렴되는 것을 확인하였다.

• 한국해양공학회지
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• 제25권6호
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• pp.56-59
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• 2011

The demand for cold rolled steel (CR) for structural members is gradually increasing. If no surface treatment (coating for corrosion resistance) for CR is conducted, its use is very limited because CR is vulnerable to corrosion. Therefore, we need to develop a coating solution to provide high corrosion resistance for CR. In this study, an organic/inorganic coating solution with Si and Ti (Si polysilicate 7 wt.% + Urethane 13 wt.% + Ti amorphous 0.5 wt.%; LR-0727(1)) was used to evaluate the corrosion resistance of CR under a salt spray test. The specimens with the LR-0727(1) coating were heat treated in a drying oven at $120{\sim}210^{\circ}C$for 5 min. The corrosion resistance was investigated using a salt spray test of 7 h. In addition, an adhesive test was conducted. Rust showed under a heat treatment of $150^{\circ}C$, but no vestiges were found over $160^{\circ}C$. The specimens with heat treatment at $160^{\circ}C$ or more did not experience delamination. From these results, it is considered that the temperature limit for optimum heat treatment is $160^{\circ}C$ considering energy efficiency.

• 한국생산제조학회지
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• 제6권1호
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• pp.59-68
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• 1997

Recently, the cases of using bonded dissimiliar materials which have each of the different components tend to increase for the purpose of developing new materials and using the special objects in the field of industry. Among the cases the strength evaluation of the joining materials of vehicle engine and the structural materials with ceramic/metal bonded joints becomes more important. But the residual stress occurs, because the joining of ceramics and metals is performed in extremely high temperature. It becomes a dominant cause to reduce the strength of the ceramic/metal bonded joints. In this paper, strength evaluation method of ceramic/metal bonded joints considering stress singularity was investigated by boundary element method and 4-point bending test. An advanced method of quantitative strength evaluation for ceramin/metal bonded joints is to be suggested.