• 열처리공학회지
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• 제36권5호
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• pp.277-284
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• 2023

Hardness and damping characteristics of fine discontinuous precipitates (DPs) microstructure generated by low temperature long term isothermal aging were investigated in comparison with those of T6 heat-treated microstructure composed of DPs and continuous precipitates (CPs) in Mg-9%Al alloy. In this study, T6 and fine DPs microstructures were obtained by isothermal aging at 453 K for 24 h and at 413 K for 336 h, respectively, after solution treatment at 693 K for 24 h. The DPs microstructure exhibited higher hardness than the T6 microstructure, which is related to the lower (α + β) interlamellar spacing of the DPs. The DPs microstructure possessed better damping capacity than the T6 microstructure in the strain-amplitude independent region, whereas in the strain-amplitude dependent region, the reverse behavior was observed. The damping tendencies depending on strain-amplitude were discussed based on the microstructural features of the T6 and DPs microstructures.

• 한국지역지리학회지
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• 제22권1호
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• pp.195-210
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• 2016

본 연구는 고온에 취약한 그룹의 특성에 대한 이해를 증진하고 고온으로 인한 사망자를 줄이는데 기여하기 위하여 사회 경제적 요인과 사망자 임계기온의 관계를 연구하였다. 연구 지역은 서울이며 연구 기간은 2000~2010년으로 선정하였다. 연구 결과, 고령 인구 비율이 높은 지역과 낮은 지역에서 사망자 임계기온은 각각 $27.6^{\circ}C$와 $27.9^{\circ}C$이었다. 고학력자 비율이 높은 지역과 낮은 지역에서 사망자 임계 기온은 각각 $27.7^{\circ}C$와 $27.4^{\circ}C$이었다. 기초생활수급자 비율에 따른 지역 구분에서는 임계기온의 차이가 나타나지 않았다. 하지만 고령 인구 비율이 높고 기초생활수급자 비율이 높은 지역에서 사망자 임계기온은 다른 지역에 비해 $0.7^{\circ}C$ 낮았다. 고령 인구 비율이 높고 고학력자 비율이 낮은 지역에서 사망자 임계기온도 상대적으로 $0.7^{\circ}C$ 낮았다. 이는 서울에서 저소득 고령층이 고온에 취약하다는 것을 보여준다. 따라서 본 연구의 결과는 고온으로 인한 사망자를 줄이기 위하여 저소득 고령 인구에 대한 정책을 우선 수립할 필요성이 있음을 시사한다.

• 한국세라믹학회지
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• 제29권8호
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• pp.630-638
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• 1992

Ta2O5 alloying into 3 mol% Y2O3-stabilized tetragonal ZrO2 polycrystals (3Y-TZP) increased the degradation during aging at 265℃ and the fracture toughness; both are determined by the amount of transformed m-ZrO2. It was proposed that the mechanism underlying the t→m transformation when aged at low temperatures is attributed to the reorientation of (Zzr'V ). complexes parallel to [111] lattice direction, which is accompanied by a relaxation of TZP lattice during annealing at low temperature. A small strain which results from the reorientation gives rise to a localized mechanical instability, thus lowering the nucleation barrier so that the t→m phase transformation (degradation) proceeds. The amount of transformed m-ZrO2 during aging becomes greater as the chemical free energy change related to the transformation, ΔGo, increases with increasing the Ta2O5 alloying content.

• 한국해양공학회지
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• 제8권2호
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• pp.157-165
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• 1994

Effect of an accelerated iso-thermal aging (375 degree C x 66days, 375 degree C x 200days) on elastic-plastic fracture resistance curve were examined in SA533B low alloy steel. Fracture toughness test are conducted by unloading compliance method at room temperature. But the apparent negative crack growth phenomenon, usually arise in partial unloading compliance test. The phenomenon of negative crack growth may be eliminated by the offset technique. There is no effect of aging on J sub(IC) and dJ/da in iso-thermal aged (375 degree C x 66 days) specimen, but there is very little effect in iso-thermal aged (375 degree C x 200 days) specimen.

• 한국항공우주학회지
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• 제31권10호
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• pp.21-26
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• 2003

본 논문에서는 광섬유 센서를 사용하여 우주환경하에 노출된 그래파이트/에폭시 복합재 적층판의 열팽창계수의 변화를 측정하였다. 열변형률과 온도를 동시에 측정하기 위해서 두개의 FBG 센서를 사용하였다. 또한 열-진공 챔버를 사용하여 고진공, 자외선, 열적 사이클 등의 인자를 가지는 저궤도(LEO) 우주환경을 모사하였다. 예비실험으로써, 본 실험에서 사용되는 온도범위에 대해 FBG 온도센서를 기준온도계로부터 보정하였고 알루미늄 시편에 부착된 FBG 변형률 센서와 변형률 게이지(ESG)의 비교실험을 통해 FBG 변형률 센서의 사용가능성을 검증하였다. 검증된 FBG센서가 삽입된 그래파이트/에폭시 복합재 평판을 모사된 우주환경에 노출하여 일정한 노화간격마다 열팽창계수 변화를 실시간으로 측정하였다. 실험결과 1000 사이클 노화후의 열팽창계수는 노화전에 비해 대체적으로 큰 변화는 없었지만 전 온도구간에서 약간 감소하는 경향을 보였다. 이러한 현상은 가스방출(outgassing), 수분방출, 모재균열 등에 기인한다.

• 대한금속재료학회지
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• 제50권7호
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• pp.511-516
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• 2012

Low temperature ${\delta}$-precipitation phenomenon below 2-step aging ($718^{\circ}C$, $8hr+621^{\circ}C$, 8 hr) temperature of cold drawn Inconel 718 alloy wire was investigated. The investigation was carried out on wires with a cold drawn ratio of 0, 20, 50 and 70% using OM, SEM, XRD, TEM, and DSC. In microstructures of 50 and 70% drawn wire, many precipitates were found along the grain boundaries and the twin boundaries in deformation band. From the results of the XRD and TEM analysis, the precipitates were identified as plate-like ${\delta}$-phase. From the results of the DSC analysis, it was also found that a temperature of ${\delta}$-precipitation decreases with an increase of the cold drawn ratio. We concluded that cold drawing of inconel 718 wire promotes the ${\delta}$-precipitation, and under the condition of a high drawing ratio, the ${\delta}$-phase could be precipitated at a temperature below the aging temperature ($718^{\circ}C$).

• 문화기술의 융합
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• 제9권5호
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• pp.753-760
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• 2023

본 연구에서는 1⁺⁺등급 소고기에 비해 1등급 저온처리 및 숙성기간에 따른 소고기의 품질향상 및 숙성효과를 시도하였다. 1⁺⁺등급 소고기의 지방함량과 전단력은 13.03%와 114.26N이었으나, 1등급 소고기는 3.21%와 149.67N이었다. 한편, 1등급 소고기를 -26℃에서 12시간 저온처리하고 0℃에서 14일간 저온 숙성한 결과 전단력은 87.85N으로 크게 감소하였으며 전체적인 기호도, 부드러움, 다즙성, 풍미 및 씹는 질감는 향상되었다. 필수 유리아미노산 함량은 1⁺⁺ 등급 소고기에서 22.17mg/100g으로 낮았으나 1등급 3개 시료에서 41.31~45.11 mg/100g으로 함량이 높았으며, 저온처리에 따른 함량 변화는 없었다. 소고기의 특정 성분으로 타우린은 30.94~34.41 mg/100g으로 소고기 등급에 따른 함량차이는 적었지만 Anserine과 Creatine은 19.68 mg/100g, 소고기 1⁺⁺등급은 70.01 mg/100g으로 낮았다. 단일불포화지방산/포화지방산 비율로서의 올레산(c18:1)/스테아르산(c18:0)의 함량비는 1⁺⁺등급 소고기는 5.29로 낮았으나 1등급 쇠고기는 6.13~6.78로 높았다. 또한 1등급 소고기는 저온처리 조건 및 숙성기간에 따른 이들 지방산의 함량비에 변화가 없었다. 본 연구 결과, -26℃에서 12시간 동안 저온 처리한 후 0℃에서 14일 동안 숙성함으로써 1등급 소고기의 품질을 향상시킬 수 있었다.

• 한국포장학회지
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• 제10권1호
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• pp.1-6
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• 2004

Amount of residual ink solvent on the packaging materials from Korea, Japan and Europe was measured and compared. The amount of packaging materials from Korea was much higher than that of Japan and Europe. To reduce the residual amounts of ink solvent, aging condition of printed packaging materials including aging time and temperature was modified and evaluated. Aging with high temperature and short time ($60^{\circ}C$ and 24 hours) was more effective for reduction of residual amount of ink solvent than that with low temperature and long time. To find out change of reduction pattern of residual amount of solvent according to plastic packaging material, several monolayer and multilayer packaging materials were selected. Among the monolayer packaging materials, the amount of EVOH and PET was lower than that of polyolefin plastic film including PE and PP. PP/EVOH/PET among the selected multilayer film showed the lowest amount of residual ink solvent on food packaging materials. Result of this research revealed that the residual amount of ink solvent can be reduced by proper selection of aging condition with and by appropriate application of mutilayer plastic film.

• Elastomers and Composites
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• 제22권2호
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• pp.109-120
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• 1987

In this study, as one of the developing ways of the functional elastomer, improvement of the functionality of CB-BR was attemped through stabilization. At first the stabilization effect of CB-BR and the concentration dependancy in CB-BR were determined. Then, triazine thiol derivative(BPTT) was synthesized by reacting p-aminodiphenylamine with cyanuric chloride. Further the functional mechanism and the effects of the antioxidants were investigated using BPTT together with other various antioxidants in liquid and solid states. The results obtained are as follows: 1) The aging of CB-BR depended on the concentration and temperature. Thus, at a low temperature of $50^{\circ}C$, the aging proceeded with gel formation; at high temperature above $100^{\circ}C$ and in above 4wt% concentration, the aging occured by the formation of gel. And in concentrations below that, the aging proceeds with a decomposition caused by oxygen attacked to elastomer molecules. 2) The effect of antioxidation of CB-BR in the liquid state was at it's best when the MBIZ and BPTT were used at $110^{\circ}C$, 4hrs after the oxidation. 3) The effect of antioxidation of CB-BR in the solid state was the best choice the simultaneous use of NDBC and BPTT at $50^{\circ}C$, 30days after the oxidation.

• 한국재료학회지
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• 제14권1호
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• pp.13-18
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• 2004

Titanium alloys are the one of promising candidate materials for medium high temperature parts in the aircraft, automobile, petrochemistry and electrochemistry because of their high strength with low density in medium high temperature. In this study, the effects of aging and heat treatments on the mechanical properties of Ti-15-3 alloy in medium high temperature, which was $400^{\circ}C$, were studied. Solid solution treatment was performed at $8000^{\circ}C$ of $\beta$ phase region for 1 h and the alloy was quenched in water. The alloy was aged at $5000^{\circ}C$ of $\alpha$ and $\beta$ two-phase region for 1, 2, 4, 8, ... and 100 h to increase the mechanical property. The $\beta$ single phase was observed at all parts of specimens in Ti-15-3 alloy after ST. As the aging at $500^{\circ}C$, fine precipitates of a phase was generated from matrix of $\beta$ phase and the microstructure was consisted of weaving structure such as Widmanstiitten a phase. The most suitable aging time is 24h in$ 400^{\circ}C$. At this time, strength is 1164 MPa and elongation is about 12%. In room temperature, elongation of Ti-15-3 alloy aged at $500^{\circ}C$ for 16 h is poor (=3%) in spite of high tensile strength (1458 MPa).