• 한국정밀공학회지
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• 제29권10호
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• pp.1137-1143
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• 2012

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft material as polymers or used as mechanical elements at high temperatures. One of the popular thermo-plastic polymers, Acrylonitrile Butadiene Styrene (ABS) which is used broadly for machine elements material, as it has excellent mechanical properties such as impact resistance, toughness and stiffness compared to other polymers, was studied for creep characteristic at different levels of stress and temperatures. From the experimental results, the creep limit of ABS at room temperature is 80 % of tensile strength which is higher than PE and lower than PC or PMMA. Also the creep limits decreased to linearly as the temperatures increased, up to $80^{\circ}C$ which is the softening temperature of Butadiene ($82^{\circ}C$). Also the secondary stage of creep among the three creep stages for different levels of stress and temperature was non-existent which occurred for many metals by strain hardening effect.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.20-23
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• 2001

Hypereutectic Al-25Si alloy, which is expected to be applied to the cylinder-liner-part of the engine-block of an automobile due to its excellent wear resistance, low density and low thermal expansion coefficient, has been fabricated through a spray forming process. The obtained microstructure of the hypereutectic Al-25Si alloy appeared to consist of Al matrix and equiaxed Si particles of average diameter of 5-7 mm. To characterize the deformation behavior of this alloy, a series of load relaxation and compression tests have been conducted at temperatures ranging from RT to $500^{\circ}C$. The strain rate sensitivity parameter (m) of this alloy has been found to be very low (0.1) below $400^{\circ}C$ and reached maximum value of about 0.2 at $500^{\circ}C$. During the deformation above $300^{\circ}C$ in compression, strain softening has been observed. The diagram of extrusion pressure vs. ram-speed has been constructed. The extrusion has been successfully conducted at the temperatures of $300^{\circ}C$ and above with the ratio of area reduction of 28 and 40 in this study.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 춘계학술대회 논문집
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• pp.816-823
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• 2007

Electric car tract plays the role of supply high electric power to the electric car from the substation by using Pantograph of the electric car. It is always exposed to the external atmosphere, which results in quite substantial fluctuations in current and voltage during operation of electric car. This generates possibility of occurrence of accident at all times. Since range of wiring metallic globe installed on the catenary cannot achieve complete electrical contact, accidents are occurring due to circulating current caused by arc caused by incomplete contact due to occurrence of hairline fracture of Pantograph due to pressure or vibration of wiring. Furthermore, rapid increase in the operational current due to increase in the operational frequency of the electric car is causing erosion and short circuit of the metallic globe at the contact points. This study on arc is generated as current transmitted out of the substation courses through power line or wiring metallic globe other than the main circuit as the current is being collected at the electric car through feeder and feeder divergence device. Accordingly, since heat generated by the arc becomes the cause for generation of circulating current due to melting of metal or softening of metal due to increase in temperature accompanying increase in contact resistance, this research shall describe causes and measures against occurrence of circulation current.

• Journal of the Korean Wood Science and Technology
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• 제25권2호
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• pp.52-60
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• 1997

Hornbeam trees(Carpinus laxiflora BL.) are growing in Korea and have good characteristics such as relatively high density, fine texture, split- resistance, and white colour. However, they have seldom been used as manufacturing materials This study was carried out to evaluate the possibility of using hornbeam wood as bent, wood furniture materials. Softening methods were steaming and micro-wave heating. The specimens of $15{\times}15{\times}350mm$ were used green or air-dried, and were steamed at $100^{\circ}C$ for 20min, or microwave heat ed f or 60 seconds. The bending processing conditions are showed in Table 3. The minimum solid-bending radii of air-dried wood were 40mm for steaming and 200mm for micro-wave heating, respectively. And that of green wood were 40mm for micro-wave heating. In conclusion, both of the steamed wood and micro-wave heated green wood showed very good solid bending processing properties, but micro-wave heated air-dried wood were not sufficient for bent-wood furniture.

• Journal of the Korean Wood Science and Technology
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• 제11권2호
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• pp.52-60
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• 1983

Hornbeam trees(Carpinus laxiflora BL.) are growing in Korea and have good characteristics such as relatively high density, fine texture, split-resistance, and white colour. However, they have seldom been used as manufacturing materials This study was carried out to evaluate the possibility of using hornbeam wood as bent-wood furniture materials. Softening methods were steaming and micro-wave heating. The specimens of $15{\times}15{\times}350mm$ were used green or air-dried, and were steamed at $100^{\circ}C$ for 20min, or microwave heated for 60 seconds. The bending processing conditions are showed in Table 3. The minimum solid-bending radii of air-dried wood were 40mm for steaming and 200mm for micro-wave heating, respectively. And that of green wood were 40mm for micro-wave heating. In conclusion, both of the steamed wood and micro-wave heated green wood showed very good solid bending processing properties, but micro-wave heated air-dried wood were not sufficient for bent-wood furniture.

• Structural Engineering and Mechanics
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• 제40권1호
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• pp.29-48
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• 2011

Under large storm loads sections of a long pipeline on the seabed can be uplifted. Numerically this loss of contact is extremely difficult to simulate, but accounting for uplift and any subsequent recontact behaviour is a critical component in pipeline on-bottom stability analysis. A simple method numerically accounting for this uplift and reattachment, while utilising efficient force-resultant models, is provided in this paper. While force-resultant models use a plasticity framework to directly relate the resultant forces on a segment of pipe to the corresponding displacement, their historical development has concentrated on precisely modelling increasing capacity with penetration. In this paper, the emphasis is placed on the description of loss of penetration during uplifting, modelled by 'strain-softening' of the force-resultant yield surface. The proposed method employs uplift and reattachment criteria to determine the pipe uplift and recontact. The pipe node is allowed to become free, and therefore, the resistance to the applied hydrodynamic loads to be redistributed along the pipeline. Without these criteria, a localised failure will be produced and the numerical program will terminate due to singular stiffness matrix. The proposed approach is verified with geotechnical centrifuge results. To further demonstrate the practicability of the proposed method, a computational example of a 1245 m long pipeline subjected to a large storm in conditions typical of offshore North-West Australia is discussed.

• Tribology and Lubricants
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• 제35권1호
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• pp.24-29
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• 2019

In this work we investigated the friction and wear characteristics of a magnesium alloy, which has been receiving much attention as a light metal in industrial applications such as automobiles and aerospace. Magnesium is one of the lightest structural material that has high specific strength, lightweight, low density and good formability. However, current issue of using magnesium alloy is that magnesium has weakness against temperature. As the temperature increases, magnesium undergoes poor creep resistance and ease of softening, and therefore, its mechanical strength decreases sharply. To solve this issue, a new type of magnesium alloy that retains high strength at high temperature has been proposed. The tribological behavior of this alloy was investigated using a tribotester with reciprocating motion and heating plate. A stainless steel ball was used as a counter surface. Results showed that extrusion process has similar wear behavior to the commonly used casting process but retains good mechanical strength and durability. The presence of an alloying element enhanced the wear properties especially in high temperature. This study is expected to be utilized as fundamental data for the replacement of high density materials currently used in mechanical industries to a much lighter and durable heat-resistant materials.

• 한국식생활문화학회지
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• 제25권1호
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• pp.82-90
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• 2010

In this study, the rheological properties of doughs blended with 5% to 20% fermented rice bran (FRB) were investigated using farinographs, amylographs, extensographs, and SEM. In the farinograph analysis, the water absorption decreased and the replacement ratio of FRB increased over the time of development of the dough. The stability time of the dough was shortened, and the degree of softening decreased with added volume of FRB. The amylograph analysis showed that the temperature at the beginning of gelatinization showed a tendency to increase with increasing replacement ratio of FRB, but the gelatinization temperature showed no significant difference between the FRB-added groups and control group. The extensograph analysis showed that when the replacement ratio of FRB was over 10%, the extension of the dough decreased while the resistance was increased. In the SEM analysis, the added dough with less than 10% FRB had similar characteristics in gluten matrix and gas bubbles to those of the control of wheat flour alone. It was concluded that an added FRB volume of below 10% is most suitable for bread making.

• 한국결정성장학회지
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• 제23권4호
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• pp.180-188
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• 2013

삼척도계지역의 탄광에서 석탄채굴시에 부산물로 발생되는 사암계 석탄폐석을 원료로 사용하여 E-glass fiber 조성의 유리를 제조하였다. 본 연구에서는 카본함량이 비교적 적은 실리카-알루미나질의 사암계 석탄폐석을 사용하였으며, 폐석의 투입량을 0~35 %까지 변화시켰다. 서로 다른 석탄폐석 투입량을 갖는 배치원료를 $1550^{\circ}C$에서 2시간 용융하여 E-glass조성을 갖는 투명하고 맑은 유리가 얻어졌고, 81~84 %의 높은 가시광투과율, $5.39{\sim}5.61{\times}10^{-6}/^{\circ}C$의 열팽창계수, 851~$860^{\circ}C$의 연화점을 나타내었다. 유리섬유 시편은 $1150^{\circ}C$에서 섬유인상장치를 통해 얻어졌고, 복합재료의 보강용 유리섬유로서 내화학성 시험과 기계적 특성평가를 위한 인장강도를 측정하였다. 그 결과 석탄폐석을 사용한 E-glass fiber의 특성이 석탄폐석을 사용하지 않은 보통 E-glass 섬유에 비해 충분히 양호한 특성을 나타내어 E-glass 섬유용 원료로서 석탄폐석의 활용가능성을 확인할 수 있었다.

• 대한토목학회논문집
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• 제37권2호
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• pp.357-367
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• 2017

강지보로 보강된 터널 숏크리트 라이닝은 그 기하학적 형태로 인해 외부하중이 작용됨에 따라 휨 모멘트와 축력이 동시에 발생하게 된다. 숏크리트는 축력 수준에 따라 휨 강성이 달라지며, 이로 인한 심한 비선형 거동을 보인다. 또한 강지보 유형에 따라 역학적으로 상이한 지보 성능을 가진다. 본 연구에서는 화이버 단면 요소(fiber section element)를 이용해 압축력과 휨 모멘트를 동시에 받는 강지보-숏크리트 라이닝의 비선형합성거동을 평가할 수 있는 수치모델을 제시하였고, 이를 활용해 강지보 유형에 따른 합성지보 성능을 수치적으로 분석하였다. 또한, 지반-구조물 상호작용을 구현하기 위해 지반의 연화(softening) 거동을 고려하여 수정된 hyperbolic 모델을 제시하였다. 제시된 수치모델은 기존 아치형 실험체의 하중실험 결과와 해석결과를 비교하여 검증하였으며, 수치해석을 통해 강지보 유형에 따른 라이닝의 합성거동을 분석하였다. 해석결과를 통해, 복철근 형태의 강지보가 기존 H형강과 유사한 극한 하중 지지력을 가지는 것을 확인하였다. 또한 강재량 증가가 잔류 지지력 향상에 크게 기여하였으며, 지보재 주변의 지반강성이 증가함에 따라 강지보 유형에 따른 최대 하중지지력 개선 효과는 작아짐을 확인하였다.