• 한국표면공학회지
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• 제55권6호
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• pp.408-416
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• 2022

In this study, the effect of Au-Sn alloy coating on reliability of electrical contacts was investigated via comparison with Au-Co alloy coating. The results show that Au-Sn alloy exhibited lower contact resistance and higher solder spreadability than those of Au-Co alloy after thermal aging. In the case of Au-Co alloy plating, the underlying Ni element diffused into Au-Co layer to form Ni oxides on surface during thermal aging, leading to increased contact resistance and decreased solder spreadability. Meanwhile, for Au-Sn alloy plating, Au-Ni-Sn metallic compound was formed at the interface between Au-Sn layer and underlying Ni layer. This compound acted as a diffusion barrier, thereby inhibiting the diffusion of Ni to Au-Sn layer during thermal aging. Consequently, Au-Sn alloy layer showed better contact reliability than that of Au-Co alloy layer.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.72-77
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• 2004

In a primary reactor cooling system(RCS), a dissimilar weld zone exists between cast stainless steel(CF8M) in a pipe and low-alloy steel(SA508 cl.3) in a nozzle. Thermal aging is observed in CF8M as the RCS is exposed for a long period of time to a reactor operating temperature between 290 and $330^{\circ}C$, while no effect is observed in SA508 cl.3. The specimens are prepared by an artificially accelerated aging technique maintained for 300, 1800 and 3600 hrs at $430^{\circ}C$, respectively. The specimens for elastic-plastic fracture toughness tests are prepared one type, which notch is created in the heat affected zone(HAZ) of CF8M. And, the specimens for fatigue crack growth tests are prepared in three classes, which notches are created at the center of deposited zone, the HAZ of CF8M, and the HAZ of SA508 cl.3. From the experiments, the J-integral values with the increase of aging time decrease, and the differences of the fatigue crack growth behaviors are relatively small in the three classes specimens.

• 대한기계학회논문집A
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• 제32권7호
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• pp.569-575
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• 2008

In this study, disk type of thermal barrier coating system for gas turbine blade was isothermally aged in the furnace changing exposure time and temperature. For each aging condition, bond tests for three samples were conducted for evaluating degradation of adhesive or cohesive strength of thermal barrier coating system. For as-sprayed condition, the location of fracture in the bond test was in the middle of epoxy which have bond strength of 57 MPa. As specimens are degraded by thermal aging, bond strength gradually decreased and the location of failure was also changed from within top coat at the earlier stage of thermal aging to the interface between top coat and TGO at the later stage due to the delamination in the coating.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.915-922
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• 2017

내열 및 내유성 고무복합체 특성연구(The study on the thermal and oil resistance rubber composite), 2016.[6] 연구에서는 고온($150^{\circ}C$, $175^{\circ}C$, $200^{\circ}C$) 조건의 고온촉진노화를 통하여 불소고무 복합체의 수명을 예측하였다. 일반적인 고무제품은 온도, 습도, 오존, 빛, 유제, 기계 및 전기적 응력 등의 특성저하 인자에 따라 다른 특성을 나타낼 가능성이 있으며, 이러한 문제를 해결하기 위하여 "내열 및 내유성 고무복합체 특성연구"[6] 연구에서 얻어진 고온촉진노화에 의한 수명 예측값과 저온촉진노화간의 인장강도 변화율 및 신장률 변화율 그리고 부피 변화율, 무게 변화율, 두께 변화율 및 열전도도를 비교 검토하였다. 검토 결과, 요구 한계수명은 모두 만족하였지만 고온촉진노화 결과와 저온촉진노화 결과 간 변화율에서 약간의 격차를 보였다. 이러한 변화율 격차가 일어나는 원인은 고온촉진노화에서는 노화 시 불소고무의 주사슬 분해로 인하여 인장강도, 신장률 감소 및 부피, 무게, 두께 증가가 일어나는데 비해 저온촉진노화에서는 $80^{\circ}C$에서 불소고무의 지속적 경화반응으로 인하여 인장강도, 신장률 및 부피, 무게, 두께 변화가 적게 나타났을 것으로 판단된다.

• 전기학회논문지
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• 제65권9호
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• pp.1518-1523
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• 2016

In this study, in order to understand the degradation characteristics of oil-paper insulation for power transformers and OF cables, tan delta was measured using cable model specimens with long-term accelerated thermal and electrical aging. In addition, to find out the degradation level due to the accelerated aging, tensile strengths of aged papers were measured. As a result, tan ${\delta}$ showed the characteristics of slight decrease at the first stage and then increase with the aging time, which could be analyzed due to the evaporation of remaining moisture and the change of aging rate with time. Also, the trend of tensile strengths with aging temperature and time was appeared to be exponentially decreased and by use of these data equivalent calculated lifetimes and accelerated aging factors were derived for each aging temperatures. After then, tan ${\delta}$ was analyzed with the equivalent operating years. For all different aging temperatures, the aged data were very well fit to the equivalent operating years and it is shown that tan ${\delta}$ was increased with the decrease of tensile strength.

• 한국압력기기공학회 논문집
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• 제20권1호
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• pp.56-65
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• 2024

Cast austenitic stainless steels (CASS) and austenitic stainless steel weldments with a ferrite-austenite duplex structure are widely used in nuclear power plants, incorporating ferrite phase to enhance strength, stress relief, and corrosion resistance. Thermal aging at 290-325℃ can induce embrittlement, primarily due to spinodal decomposition and G-phase precipitation in the ferrite phase. This study evaluates the effects of thermal aging by collecting and analyzing various mechanical properties, such as Charpy impact energy, ferrite microhardness, and tensile strength, from various literature sources. Different model expressions, including hyperbolic tangent and phase transformation equations, are applied to calculate activation energy (Q) of room-temperature impact energies, and the results are compared. Additionally, predictive models for Q based on material composition are evaluated, and the potential of machine learning techniques for improving prediction accuracy is explored. The study also examines the use of ferrite microhardness and tensile strength in calculating Q and assessing thermal embrittlement. The findings provide insights for developing advanced prediction models for the thermal embrittlement behavior of CASS and the weldments of austenitic steels, contributing to the safety and reliability of nuclear power plant components.

• 펄프종이기술
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• 제43권2호
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• pp.24-30
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• 2011

The accelerated aging characteristics of electroconductive papers manufactured with a mixture of carbon fiber were investigated by heating in dry oven. By accelerated aging time, the tensile strength, tensile stretch of the papers were decreased more slowly with increase of carbon fiber content, but the electrical conductivity was more rapidly decreased in case of high carbon fiber content. The weight loss of papers by thermal analysis were reduced as increasing the carbon fiber content. These results were indicated that the electrical conductivity of carbon fiber was diminished easily by heat aging, but thermal characteristic of carbon fiber was much better than that of wood pulp.

• 접착 및 계면
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• 제3권2호
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• pp.40-44
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• 2002

본 실험에서는 고무-황동 도금 스틸 코드 복합체의 접착성에 미치는 미가류 복합체의 방치 기간과 가류 복합체의 열노화의 영향을 검토하였다. 또한 이런 방치 조건에 따른 접착력 변화가 타이어 내구력에 어떤 영향을 미치는지를 평가하였다. PAD 접착 시편을 사용하여 박리 접착 강도를 측정하였다. 미가류 복합체의 방치 기간은 공장 조건에서 최대 35일이고 가류 복합체의 열노화는 $85^{\circ}C$ 항온조에서 5, 10일간 실시하였다. 박리 접착 강도는 방치일수가 길수록 하락하는 경향을 보였다. 또한 열노화 기간이 길수록 그 값은 낮았다. 박리 접착 강도가 낮을수록 타이어 내구력도 낮았고, 그 주된 원인이 수분과 열에 의한 노화가 고무와 스틸 코드의 접착력을 하락시켜 코드와 고무의 계면에서 파괴가 일어났기 때문이라는 것을 SEM관찰과 내구력 평가로 확인할 수 있었다. 즉, 스틸 코드 표면의 부식이나 접착증의 노화가 접착강도 하락에 크게 영향을 미치고 그 결과 타이어의 내구력 하락에도 직접적인 영향을 미친다는 것을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제48권2호
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• pp.518-524
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• 2016

The thermal aging effects on mechanical properties and microstructures in China low-activation martensitic steel have been tested by aging at $550^{\circ}C$ for 2,000 hours, 4,000 hours, and 10,000 hours. The microstructure was analyzed by scanning and transmission electron microscopy. The results showed that the grain size and martensitic lath increased by about $4{\mu}m$ and $0.3{\mu}m$, respectively, after thermal exposure at $550^{\circ}C$ for 10,000 hours. MX type particles such as TaC precipitated on the matrix and Laves-phase was found on the martensitic lath boundary and grain boundary on aged specimens. The mechanical properties were investigated with tensile and Charpy impact tests. Tensile properties were not seriously affected by aging. Neither yield strength nor ultimate tensile strength changed significantly. However, the ductile-brittle transition temperature of China low-activation martensitic steel increased by $46^{\circ}C$ after aging for 10,000 hours due to precipitation and grain coarsening.

• 한국태양에너지학회 논문집
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• 제37권4호
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• pp.35-47
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• 2017

Energy efficiency solutions are being pursued as a sustainable approach to reducing energy consumption and related gas emissions across various sectors of the economy. Vacuum Insulation Panel (VIP) is an energy efficient advanced insulation system that facilitates slim but high-performance insulation, based on a porous core material evacuated and encapsulated in a barrier envelope. Although VIP has been applied in buildings for over a decade, it wasn't until recently that efforts have been initiated to propose and adopt a global standard on characterization and testing of VIP. One of the issues regarding VIP is its durability and aging due to pressure and moisture dependent increase of the initial low thermal conductivity with time; more so in building applications. In this paper, the aging of commercially available VIP was investigated experimentally; thermal conductivity was tested in accordance with ISO 8302 standard (guarded hot box method) and long-term durability was estimated based on a non-linear pressure-humidity dependent equation based on study of IEA/ECBCS Annex 39, with the aim of assessing durability of VIP for use in buildings. The center-of-panel thermal conductivity after 25 years based on initial 90% fractile with a confidence level of 90 % for the thermal conductivity (${\lambda}90/90$) ranged from 0.00726-0.00814 (W/m K) for silica core VIP. Significant differences between manufacturer-provided data and measurements of thermal conductivity and internal pressure were observed.