• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.516-528
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• 2009

Form the application of long rail system the non-ballast steel plate bridges, fatigue strength increase and rail noise reduction can be expected. This is mainly form the reduction of the rail impact at the rail joint locations which already made to behave together from welds. In the high speed rail, application of long rail system is essential because without long rail system, the required serviceability level can not be achieved. But even with this long rail systems, the thermal expansion from the girder can not be absorbed in the normal bearing systems, and these expansion cause between girder and rail. Also unexpected rail buckling and fracture through rail thermal tension may happen. It was found through numerical analysis and field measurement that these problems can be avoided by semi-fixed bearing system. In this study, the benefits of non-ballast plate bridge through long rail system, especially at the point of girder stability, girder stiffness increase and bearing maintenance will be reviewed.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 추계학술대회 논문집
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• pp.324-327
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• 2003

The needs for the cryocooler which has high reliability and long MTTF are increased in the military and commercial thermal imaging system The gas contamination wear, leakage of the working fluid, fatigue and etc. have the significant effects on the reliability and MTTF(Mean Time To Failure) or MTBF(Mean Time Between Failure) of the Stirling cryocooler. In the KIMM, the Stilting cryocooler with the linear compressor was released after the several performance tests were performed. This paper describe the experimental facility for the MTTF evaluation and some typical results of the Stilling cryocooler.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.263-266
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• 2000

Effects of excess Pb(50 mole ％) on the crystallization properties of amorphous PZT thin films on the glass substrates by post-annealing in oxygen ambient were investigated to lower the crystallization temperature of the PZT thin films with a single perovskite phase. The PZT thin films(350nm) were prepared on Pt/Ti/corning glass(1737) substrates. The PZT thin films and bottom electrode were deposited by RF magnetron sputtering. Crystallization properties of PZT thin films were strongly dependent on RTA(Rapid Thermal Annealing) temperature. We were able to obtain a perovskite structure of PZT at 600$^{\circ}C$ for 10min. After thermal treatments were done, electrical properties such as I-V, P-E, and fatigue were measured.

• 대한기계학회논문집A
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• 제28권4호
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• pp.394-401
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• 2004

In this study the mechanical behaviors of fiber metal laminates(FMLs) such as ARALL, GLARE and CARE which are recently developed as new structural materials and known to have excellent fatigue resistant characteristics while with relatively low densities compared to the conventional aluminum materials, are considered through the classical lamination theory. The mechanical properties such as elastic moduli, thermal expansion coefficients and hygro-thermally induced residual stresses in the fiber metal laminates are obtained and compared each other. Also, carpet plots of effective elastic moduli, Poisson's ratio and the thermal expansion coefficient for GLARE FML are plotted.

• 비파괴검사학회지
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• 제36권3호
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• pp.175-180
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• 2016

Nondestructive evaluation for material health monitoring is important in aerospace industries. Composite laminates are exposed to heat cyclic loading and humid environment depending on flight conditions. Cyclic heat loading and moisture absorption may lead to material degradation such as matrix breaking, debonding, and delamination. In this paper, the moisture absorption ratio was investigated by measuring the Lamb wave velocity. The composite laminates were manufactured and subjected to different thermal aging cycles and moisture absorption. For various conditions of these cycles, not only changes in weight and also ultrasonic wave velocity were measured, and the Lamb wave velocity at various levels of moisture on a carbon-epoxy plate was investigated. Results from the experiment show a linear correlation between moisture absorption ratio and Lamb wave velocity at different thermal fatigue stages. The presented method can be applied as an alternative solution in the online monitoring of composite laminate moisture levels in commercial flights.

• Corrosion Science and Technology
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• 제18권2호
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• pp.49-54
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• 2019

The purpose of this paper is to present failure analysis, of the heat exchanger tube in a district heating system. SS304 stainless steel is used, as material for the heat exchanger tube. The heat exchanger operates in a soft water environment containing a small amount of chloride ions, and regularly repeats operation and standstill period. This causes concentration of chloride ions on the outer surface of the tube, as well as repeat of thermal expansion, and shrinkage of the tube. As a result of microscopic examination, cracks showed transgranular as well as branched propagation, and many pits were present, at the initiation point of each crack. Energy disperstive spectroscopy analysis showed Fe and O peak, as well as Cl peak, meaning that cracks were affected by Cl ion. Failure of the tube was caused by chloride-induced stress corrosion cracking by thermal stress, high temperature, and localized enrichment of chloride ions.

• 터널과지하공간
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• 제24권2호
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• pp.166-175
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• 2014

본 연구에서는 현장실측을 통하여 강원도 태백에 위치한 대규모 석탄광산의 열환경을 평가하였다. 열환경 평가를 위하여 WBGT, HSI, ESI, KATA지수 및 유효온도 등 다양한 열적지표를 적용하였고, 상관분석을 실시하였다. 분석결과 대부분의 작업장에서 높은 열환경이 평가되었고, 특히 열적지표 중 인체의 생리학적 특성을 반영하는 HSI와 최대 땀증발열의 상관계수는 -0.834이고 이것은 HSI지표에 가장 큰 영향을 미치는 것으로 나타났다. 최대 땀증발열에 가장 큰 영향을 미치는 인자는 공기속도이다. 따라서 운영 중인 제 1수직갱의 연장 굴착 또는 공기 누기를 방지하기 위한 구조물을 설치함으로써 환기량 증대를 통해 작업장의 열환경을 개선시킬 수 있을 것으로 판단된다.

• 한국표면공학회지
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• 제32권2호
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• pp.144-156
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• 1999

Thermal Barrier Coating with Functional Gradient Materials (FGM-TBC) can play an important role to protect the parts from harmful environments in high temperatures such as oxidation, corrosion, and wear and to improve the efficiency of aircraft engine by lowering the surface temperature on turbine blade. FGM-TBC can increase the life spans of product and improve the operating properties. Therfore, in this study the evaluations of mechanical and thermal properties of FGM-TBC such as fatigue, oxidation and wear-resistance at high temperatures have been conducted. The samples of both the TBC with 2, 3, 5 layers (YSZ/NiCrAlY) to be produced by Air Plasma Spray method (APS) and the bulk TBC with 6 layers to be produced by Plasma Assisted Sintering method (PAS) were used. Furthermore, residual stress, bond strength, and thermal conductivity were evaluated. The average thickness of the APS was 500$\mu\textrm{m}$ to 600$\mu\textrm{m}$ and the average thickness of the PAS was 3mm. The hardness number of the top layer of APS was 750 Hv to 810Hv and that of PAS was 950 Hv to 1440Hv. The $ZrO_2$ coating layer of APS was composed of tetragonal structure after spraying as the result of XRD analysis. As shown in the results of the high temperature wear test, the 3 layer coating of APS had the best wear resistance at $800^{\circ}C$ and the 5 layer coating of APS had the best wear resistance at $600^{\circ}C$. But, these coatings had the tendency of the low-temperature softening at $300^{\circ}C$. The main mechanism of wear was the adhesive wear and the friction coefficient of coatings was increased as increasing the test temperatures. A s results of thermal conductivity test, the ${\Delta}T$ of the APS coating was increased as number of layer and the range of thermal conductivity of the PAS was $800^{\circ}C$ to $1000^{\circ}C$.

• 해양환경안전학회지
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• 제27권4호
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• pp.521-528
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• 2021

본 연구는 손상된 선박용 절탄기 핀튜브에 대하여 보수를 목적으로 Inconel 625 아크 열용사 코팅기술 적용 후 실링처리를 실시하였다. 모재(Substrate), 열용사 코팅(Thermal Srpay Coating; TSC) 그리고 열용사 코팅+실링처리(TSC+Sealing) 시편에 대하여 내구성을 평가하기 위해 ASTM G76-05에 의거하여 고상입자 침식(Solid Particle Erosion; SPE) 실험을 실시하였다. 표면 손상 형상은 주사전자현미경과 3D 레이져 현미경을 통해 관찰했으며, 무게 감소량과 표면 거칠기 분석을 실시하여 내구성을 평가하였다. 그 결과 내구성은 TSC와 TSC+Sealing에 비해 Substrate가 우수하게 나타났으며, 이는 TSC 층 내에 존재하는 다수의 기공 결함에 기인한 것으로 판단된다. 또한 고상입자 침식 손상 메카니즘은 Substrate의 경우 연성 재질 특성인 소성변형과 피로에 의한 균열 생성이 동반되었으며, TSC와 TSC+Sealing의 경우 취성파괴 경향이 확인되었다.

• 한국분말재료학회지
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• 제26권6호
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• pp.515-527
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• 2019

High-entropy alloys (HEAs) are generally defined as solid solutions containing at least 5 constituent elements with concentrations between 5 and 35 atomic percent without the formation of intermetallic compounds. Currently, HEAs receive great attention as promising candidate materials for extreme environments due to their potentially desirable properties that result from their unique structural properties. In this review paper, we aim to introduce HEAs and explain their properties and related research by classifying them into three main categories, namely, mechanical properties, thermal properties, and electrochemical properties. Due to the high demand for structural materials in extreme environments, the mechanical properties of HEAs including strength, hardness, ductility, fatigue, and wear resistance are mainly described. Thermal and electrochemical properties, essential for the application of these alloys as structural materials, are also described.