• 한국전기전자재료학회논문지
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• 제16권9호
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• pp.842-850
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• 2003

The suspension insulators are subjected to harsh environments in service for a long time. The long-term reliability of tile insulators is required for both mechanical and electrical performances. This study describes some basic performance tests and accelerated aging test by cool-heat cycling methods and thermal mechanical performance test methods on alumina porcelain insulators (new and aged) used for transmission line in KOREA. There was no fail in electrical and mechanical performance tests such as a high voltage strength, a flashover voltage, and an impact strength in all samples. But in the case of accelerating aging tests which have above 9$0^{\circ}C$ temperature gradient, fracture phenomena was happened by a thermal shock in tile aged sample(sample A) with low alumina porcelain body. It was indicated that sample A was more severely aged than other samples. According to results of HRB test and microstructural analysis, it was reasoned that insulator bodies with the matrix reinforced with alumina crystalline phase have advantages over the suppression of crack advance. And cool-heat aging and mechanical thermal ageing tests shows that a temperature gradient is more effective to accelerating than a cycling number.

• 한국기계기술학회지
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• 제20권6호
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• pp.818-823
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• 2018

In this study, the effect of pre-aging treatment for inhibition of natural aging of Al-4.8Zn-1.3Mg alloy by extrusion process was investigated. Firstly, the as-cast microstructure of Al-4.8Zn-1.3Mg alloy billet and its evolution during homogenization($460^{\circ}C$, $4h+510^{\circ}C$, 5h) were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), hardness analysis. The as-cast microstructures of Al-4.8Zn-1.3Mg alloy reveal $Mg_2Zn$, $Al_5Cu$, $Al_{13}Cu$ formed between dendrities. After homogenization, MgZn, $Al_4Cu$, $Al_{13}Cu$ phases precipitated into the matrix. In addition, standard deviation of homogenized billet was improved than as-cast billet from 2.62 to 0.99. According to pre-aging($100^{\circ}C$, 1h) Al-4.8Zn-1.3Mg alloy by extrusion process, yield strength and tensile strength deviation improved more than condition by natural aging.

• 대한금속재료학회지
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• 제49권3호
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• pp.197-202
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• 2011

This study was carried out to investigate the precipitation behavior of ${\chi}$ phase and effect of ${\chi}-phase$ which precipitated at the initial stage of aging on mechanical properties of 25%Cr-7%Ni-4%Mo-0.2%N super duplex stainless steel. ${\chi}-phase$ was precipitated mainly at the interface of ferrite / austenite phases and inside of the ferrite phase at the initial stage of aging, and it was transformed into ${\sigma}-phase$ with an increase of aging time. The ferrite phase was decomposed into new $austenite({\gamma}_2)phase$ and ${\sigma}-phase$ by aging treatment. The hardness and tensile strength of the initial stage of aging when ${\chi}-phase$ was precipitated did not changed considerably, while elongation rapidly decreased. Accordingly, it is considered that ${\chi}-phase$ didn't affect the hardness and strength significantly, but it affected the elongation.

• 한국정밀공학회지
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• 제33권2호
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• pp.149-155
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• 2016

In this study, we investigated the adhesive strength by molecular weight, mixture ratio, coating thickness, lamination temperature and aging condition of adhesive in manufacture process of Nylon-Aluminum for secondary aluminum pouch. It found that as the molecular weight of adhesive gets lower, the adhesive strength increases. In the mixture ratio, as the content of hardener get higher and as the content of solvent get lower, the adhesive strength increases. Also, as the coating thickness of adhesive get thicker, the adhesive strength increase. In addition, the adhesive strength is higher at 90 degrees of lamination temperature. So, it found that 90 degrees of lamination temperature is appropriate. In the aging condition when aged for 5 days, it found that the reaction and curing of adhesive is sufficient by measuring the adhesive strength.

• 콘크리트학회논문집
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• 제13권3호
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• pp.237-243
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• 2001

본 논문에서는 플라이애시 콘크리트의 재령에 따른 변화를 예측하기 위한 모델식을 제시하고 그 모델식의 유효성을 검토하였다. 기존에 행해졌던 실험결과를 모델식을 이용하여 회귀분석한 후에 그 결과를 플라이애시 대체량과 물-시멘트비에 따라 분석하였다. 해석결과에 의하면 예측 모델식은 실험결과를 일정오차내에서 잘 모델링하였다. 그러나 물-시멘트비가 매우 작은 경우에는 플라이애시 대체량이 증가하면 실험값과 예측값의 오차가 조금 증가하는 경향을 나타내었다. 플라이애시 대체량이 증가할수록 한계상대압축강도의 크기가 증가하였고 초기 겉보기 활성에너지도 한계상대압축강도와 같이 플라이애시 대체량이 증가할수록 증가하였다. 0.40이하의 물-시멘트비에서는 한계상대압축강도와 겉보기 활성에너지의 크기가 일정하고 물-시멘트비가 0.40을 초과하면 물-시멘트비의 증가에 따라 한계상대압축강도와 겉보기 활성에너지가 조금씩 증가하였다.

• 조명전기설비학회논문지
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• 제20권9호
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• pp.61-69
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• 2006

The tensile strength of an overhead transmission line's conductor in response to an aging is being assessed in this paper. It is our view that, the decrement in the conductor's tensile strength is a key index that can be used to determine a conductor's end of life and a current limits. This paper describes a probabilistic method of assessing this index for main transmission lines which are responsible for the north bound power flow in the Seoul metropolitan area. Such an assessment can be a useful guide for economic system operation.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.31-35
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• 2006

Degradation characteristics of filament-winded composites due to accelerated environmental aging have been evaluated under high temperature, water immersion and thermal impact conditions. Two kinds of laminated composites coated by an urethane resin have been used: carbon-fiber reinforced epoxy(T700/Epon-826, CFRP) and glass-fiber reinforced phenolic (E-glass/phenolic, GFRP). For tensile strength of $0^{\circ}$ composites, CFRP did high reduction by 25% under the influence of high temperature and water while CFRP showed little degradation. However for water-immersed $90^{\circ}$ composites both CFRP and GFRP showed high reduction in tensile strength. Bending strength and modulus of $90^{\circ}$ composites were largely reduced in water-immersion as well as high temperature environment. Urethane coating on the composite surface improved the bending properties by 20%, however hardly showed such improvement for water-immersed $90^{\circ}$ composites.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2017년도 추계 학술논문 발표대회
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• pp.5-6
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• 2017

This study is to analyze the properties of concrete according to the types of binders and cement powder and to utilize them as fundamental data for the development of early strength concrete. In the case of fluidity, all of the formulations satisfied the 180±25mm, and the flowability of HSF was decreased by high fineness cement. For the air content, 4.5±1.5% of the total content was satisfied. Compressive strength of HSF was found to satisfy the 5MPa in 2days of aging. In case of 28 days of aging, the strength of HSF was more than 24MPa.

• 대한기계학회논문집 C: 기술과 교육
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• 제4권2호
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• pp.101-109
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• 2016

발전소 내열강의 물성치는 고온 가동시간이 누적됨에 따라 열시효의 영향을 받는다. 본 연구에서는 제 4 세대 원자력시스템의 재료로 널리 채택되고 있는 Mod.9Cr-1Mo (ASME Grade 91)강을 대상으로 항복강도, 인장강도 및 파괴거동에 열시효가 미치는 영향에 대해 조사 및 분석하였다. 국내에서 가동 중인 초초임계(USC) 화력발전소의 배관계통에서 채취한, 73,716 시간의 가동 이력을 겪은 Gr.91 강 재료가 재료 실험을 위해 사용되었고, 동 시험결과와 가동 이력을 겪지 않은 신재의 시험결과를 비교 분석하였다. 또한 ASME 코드의 물성치와 RCC-MRx 의 물성치와 비교 분석하였고, 이들 설계기술기준 물성치의 보수성은 신재 및 가동 이력을 겪은 재료의 시험결과와 비교 분석을 통해 정량화하였다.

• 한국재료학회지
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• 제23권1호
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• pp.18-23
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• 2013

In this study, the effects of cryogenic treatment cycles on the residual stress and mechanical properties of 7075 aluminum alloy (Al7075) samples, in the form of a tube-shaped product with a diameter of 500 nm, were investigated. Samples were first subjected to solution treatment at $470^{\circ}C$, followed by cryogenic treatment and aging treatment. The residual stress and mechanical properties of the samples were systematically characterized. Residual stress was measured with a cutting method using strain gauges attached on the surface of the samples; in addition, tensile strength and Vickers hardness tests were performed. The detailed microstructure of the samples was investigated by transmission electron microscopy. Results showed that samples with 85 % relief in residual stress and 8% increase in tensile strength were achieved after undergoing three cycles of cryogenic treatments; this is in contrast to the samples processed by conventional solution treatment and natural aging (T4). The major reasons for the smaller residual stress and relatively high tensile strength for the samples fabricated by cryogenic treatment are the formation of very small-sized precipitates and the relaxation of residual stress during the low temperature process in uphill quenching. In addition, samples subjected to three cycles of cryogenic treatment demonstrated much lower residual stress than, and similar tensile strength compared to, those samples subjected to one cycle of cryogenic treatment or artificial aging treatment.