• Journal of Welding and Joining
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• 제3권2호
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• pp.42-51
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• 1985

The dynamic fracture toughness, fracture characteristics, impact tension and tensile properties of Al-Mg-Si T5 alloy and Al-Zn-Mg T6 alloy respectively welded with filler metal of Alcan 4043 were investigated. The dynamic fracture toughness values were obtained rapidly and simply for the specimen of small size by using instrumented Chirpy impact testing machine. the testing temperatures of the specimen were a range of room temperature and-196.deg. C. The results obtained in this experiment are summarized as follows. With decreasing the testing temperatures, dynamic tensile stress and fracture load were increased, on the other hand the deflection and impact value showed decreasing tendency in order of base metal>HAZ>weld. Changes of total absorbed energy were more influenced by the crack propagation energy than the crack initiation energy. At the low temperatures, the unstable rapid fracture representing the crack propagation appeared for the specimens of Charpy press side notched in Al-Zn-Mg alloy, but it was difficult to obtain the unstable rapid fracture in Al-Mg-Si alloy. Because of the development of plastic zone at the notch root, it was difficult to obtain thevalid $K_{1d}$ value in Al-Mg-Si alloy. Therefore the fatigue cracked specimens were effective in both Al-Mg-Si and Al-Zn-Mg alloys. With decreasing the impact testing temperatures, specimens underwent a transition from dimple-type transgranular fracture to lamella surface-type intergranular fracture because of the precipitate at the grain boundaries, impurities and crystal structure of the precipitates.s.

• The Korean Journal of Ceramics
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• 제3권3호
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• pp.199-207
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• 1997

$Al_2O_3$/SiC particulate composites were fabircated by pressureless sintering. The dispersed phase was SiC of which the content was varied from 1.0 to 10 vol%. Three SiC powders having different median diameters from 0.28 $\mu\textrm{m}$ to 1.9 $\mu\textrm{m}$ were used. The microstructure became finer and more uniform as the SiC content increased except the 10 vol% specimens, which were sintered at a higher temperature. Under the same sintering condition, densification as well as grain growth was retarded more severly when the SiC content was higher or the SiC particle size was smaller. The highest flexural strength obtained at 5.0 vol% SiC regardless of the SiC particle size seemed to be owing to the finer and more uniform microstructures of the specimens. Annealing of the specimens at $1300^{\circ}C$ improved the strength in general and this annealing effect was good for the specimens containing as low as 1.0 vol% of SiC. Fracture toughness did not change appreciably with the SiC content but, for the composites containing 10 vol% SiC, a significantly higher toughness was obtained with the specimen containing 1.9$\mu\textrm{m}$ SiC particles.

• 한국주조공학회지
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• 제2권2호
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• pp.2-9
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• 1982

This paper is concerned with the improvement of impact and tensile Properties of spheroidal graphite cast iron of the following duplex matricess which were heat treated in the eutectic transformation temperature range (that is, $({\alpha}+{\gamma})$ coexisting range) ; ferrite-martensite, ferrite-bainite and ferrite-pearlite. The absorbed energy and maximum load was measured by recording the load-deflection curve with instrumented Charpy impact testing machine in the temperature range from $+100^{\circ}C$ to $-196^{\circ}C$. It was found the ferrite-bainite duplex matrix showed the highest toughness among the above matrices in the room temperature and the low temperature range. Comparison of this matrix to ferrite-pearlite matrix(that is, as cast) showed a lowering of $27^{\circ}C$ in the nil-ductility transition temperature (NDT) and a lowering of $40^{\circ}C$ in the ductile-brittle transition temperature (TrE), Which seems to result from the finner dimple pattern observed using miorofractography.

• 한국가스학회지
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• 제10권1호
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• pp.1-6
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• 2006

압력설비를 안전하고 효율적으로 사용하기 위하여 본 연구에서는 API-581 절차에 의한 위험기반검사에서 취성파괴에 의한 사고발생 가능성을 정량적으로 해석하였다. 그 결과, 낮은 온도/낮은 인성파괴와 뜨임취성에서는 A 충격곡선이고. 낮은 온도와 열처리 전인 상태에서 기술종속계수(TMSF)가 큰 값을 나타내었고, $855^{\circ}F$ 취성에서는 위험도가 무시할 수 있었으나, 시그마상 취성에서는 낮은 온도의 고 시그마인 경우에 TMSF가 큰 값을 나타내어 사고발생 가능성이 매우 높았다.

• 접착 및 계면
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• 제10권4호
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• pp.162-168
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• 2009

극저온 온도에서 최적복합재료물성치의 사전 연구로서, 실온과 저온, 즉 $25^{\circ}C$와 $-10^{\circ}C$에서 카본 혹은 유리섬유가 함침된 에폭시 복합재료의 계면 물성치가 미세역학인 시험법을 사용하여 평가되었다. 인장과 압축하중 조건에서 저온에서의 기계적인 강성도가 상온에서의 강성도보다 증대하였다. 실온과 저온에서의 계면전단강도가 에폭시 기지의 인성과 겉보기 강성도를 사용하여 상호 비교하였다. 기지의 강성도 향상으로 인해 계면전단강도가 실온보다 저온에서 높게 나타났다. 유리와 카본 섬유의 인장 강도들의 통계적인 분포가 다른 온도의 범위 평가되었고, 이것들은 섬유의 고유결함과 견고함에 의해서 결정된다.

• 한국강구조학회 논문집
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• 제23권4호
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• pp.483-491
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• 2011

본 연구에서는 구조용강재의 샤르피 충격시험(Charpy Impact Test)을 통해 저온에서의 충격 인성(Impact Toughness) 평가를 실시하여 사용 가능 온도를 파악함으로써 강재의 극한지 적용성을 검토하였다. 본 시험에 사용된 강재는 용접구조용강 중 현재 가장 널리 쓰이는 강종인 SM490B와 TMCP (Thermo-Mechanical Control Process)법에 의해 제조된 고강도 강재인 SM570-TMC이다. 또한, 본 시험결과와의 비교를 위해 남극 세종기지 건설시 사용실적이 있는 일반구조용강인 SS400에 대해서도 시험을 수행하였다. 대부분의 강구조물은 용접에 의해 제작되므로, 강재의 극한지 적용성 검토를 위해 용접시험판을 제작하여 모재(Base Metal), 용접금속(Weld Metal) 및 열양향부(Heat Affected Zone)에 대해서 충격시험을 실시하였다. 단, SS400의 경우에는 용접구조용강재가 아니므로 모재에 대해서 충격시험을 실시하였다. 대상 강재의 샤르피 충격시험을 통해서 저온에서의 충격흡수에너지 값을 구하고 이를 강재의 항복응력에 따른 충격흡수에너지의 기준값과 비교함으로써 강재의 사용온도를 결정하였으며, 이를 통해서 구조용강재의 극한지 적용성을 검토하였다.

• 한국표면공학회지
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• 제55권6호
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• pp.368-375
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• 2022

YSZ (Yttria Stabilized Zirconia) is used as a thermal barrier coating material for gas turbines due to its low thermal conductivity and high fracture toughness. However, the operating temperature of the gas turbine is rising according to the market demand, and the problem that the coating layer of YSZ is peeled off due to the volume change due to the phase transformation at a high temperature of 1400℃ or higher is emerging. To solve this problem, various studies have been carried out to have phase stability, low thermal conductivity, and high fracture toughness in a high temperature environment of 1400℃ or higher by doping trivalent and tetravalent oxides to YSZ. In this study, the monoclinic phase formation behavior and crystallinity were comparatively analyzed according to the total doping amount of oxides by controlling the doping amounts of Sc₂O₃ and Gd₂O₃, which are trivalent oxides, and TiO₂, which are tetravalent oxides, in YSZ. Through comparative analysis of monoclinic phase formation and crystallinity, the thermal conductivity of the thermal barrier coating layer according to the amount of doping was predicted.

• 한국안전학회지
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• 제23권1호
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• pp.1-11
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• 2008

In this study, small punch test and tensile test were performed with specimens directly machined from an ASTM A53 grade B carbon steel pipe at which an explosion accident was occurred in the Heavy Oil Unit. Main damage mechanism of the pipe was known as a high temperature hydrogen attack(HTHA). Effects of HTHA on the mechanical strength change of the A53B steel were studied in detail. Small punch test results have showed that maximum reaction forces, SP energy and ductility were decreased at hydrogen attacked part of the pipe compared with sound part of the pipe. Yield strength and tensile ultimate strength were calculated with the obtained small punch test curve results using different methods and compared the estimation methods. Small punch test simulation has been also performed with the finite element method and then mechanical strength, equivalent strain and fracture toughness were calculated with the obtained numerical analysis results. It was shown that the fracture toughness data calculated from small punch equivalent energy obtained by the finite element analysis for SP test was very low at the hydrogen attacked part.

• Nuclear Engineering and Technology
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• 제46권3호
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• pp.413-422
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• 2014

Presented in this study are the variations of microstructures and mechanical properties with tempering and Post-Weld Heat Treatment (PWHT) conditions for SA508 Gr.4N steel used as Reactor Pressure Vessel (RPV) material. The blocks of model alloy were austenitized at the conventional temperature of $880^{\circ}C$ then tempered and post-weld heat treated at four different conditions. The hardness and yield strength decrease with increased tempering and PWHT temperatures, but impact toughness is significantly improved, especially in the specimens tempered at $630^{\circ}C$. The sample tempered at $630^{\circ}C$ with PWHT at $610^{\circ}C$ shows optimum mechanical properties in hardness, strength, and toughness, excluding only the transition property in the low temperature region. The microstructural observation and quantitative analysis of carbide size distribution show that the variations of mechanical properties are caused by the under-tempering and carbide coarsening which occurred during the heat treatment process. The introduction of PWHT results in the deterioration of the ductile-brittle transition property by an increase of coarse carbides controlling cleavage initiation, especially in the tempered state at $630^{\circ}C$.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 제5회 압연심포지엄 신 시장 개척을 위한 압연기술
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• pp.216-222
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• 2004

The caster roll shells have the good thermal conductivity and the low thermal expansion and have to exhibit high enough strength and good ductility at temperature up to $600^{\circ}C$. Thermal stress in particular is very high due to the contact with the liquid aluminium. The main stresses are of thermal origin, which bring a plastic fatigue on surface. This paper will represent one survey about the investigation of the failure of roll shells for continuous casters and an analysis using the simulation of the temperature distribution and the state of stress during hot rolling. Moreover, there will be a discussion on the roll shell of Mod. HAR 5 which is developed by heat treatment process. Mod. HAR 5 has advantages of high strength, high toughness and increased thermal stress resistance while maintaining the same productivity as the conventional roll.