• 한국건설순환자원학회논문집
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• 제4권1호
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• pp.74-80
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• 2009

본 연구는 BS를 다량 치환한 콘크리트의 양생온도에 따른 초기품질특성을 검토하여, 온도의존성을 분석한 것으로, 그 결과를 요약하면 다음과 같다. 먼저, 굳지않은 콘크리트의 특성으로 BS 치환율이 증가할수록 유동성은 증가하고, 공기량은 미세하게 감소하는 것으로 나타났다. 응결시간은 전반적으로 BS 치환율이 증가할수록 양생온도가 낮을수록 지연되는 것으로 나타났는데, 단, 양생온도 $35^{\circ}C$의 경우 BS 치환율 80%의 경우라도 $5^{\circ}C$, $20^{\circ}C$의 Plain에 비해 응결시간이 크게 촉진되는 것으로 나타나, 온도의존성이 매우 큰 것을 알 수 있었다. 경화 콘크리트의 특성으로 압축강도는 전반적으로 BS 치환율이 증가하고 양생온도가 낮아질수록 초기 압축강도는 비례적으로 저하하였는데, 양생온도가 높을수록 BS 치환율 증가에 따른 강도 저하폭이 상당부분 감소하여, 역시 온도의존성이 매우 중요함을 알 수 있었다.

• 소성∙가공
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• 제14권7호
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• pp.607-612
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• 2005

In this paper, warm deep drawing process with local heating and cooling technique was attempted to improve the formability of AZ31 magnesium alloy which is impossibly to form by conventional methods at room temperature by finite element method and experiment. For FE analysis, in first model with considering heat transfer, both die and blankholder were heated to 573K while the punch was kept at room temperature by cooling water. Also distribution of thickness and von Mises stress at room temperature and 498k for warm deep drawing were compared by FEM. Uniaxial tension tests at elevated temperature were done in order to obtain the temperature dependence of material constant under temperature of $293K\~573K$ and cross head velocity of $5\~500mm/min$. The phenomenological model for warm deep drawing process in this work was based on the hardening law and power law strain rate dependency. Deep drawing experiment were conducted at temperatures of room temperature, 373K, 423K, 473K, 498K, 523K, and 573K for the blank and deep drawing tools(holder and die) and at a punch speed of 10mm/min.

• Geomechanics and Engineering
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• 제18권2호
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• pp.133-140
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• 2019

Strain-rate and temperature have significant effects on the one-dimensional (1D) compression behavior of soils. This paper focuses on the bonding degradation effect of soil structure on the time and temperature dependent behavior of soft structured clay. The strain-rate and temperature dependency of preconsolidation pressure are investigated in double logarithm plane and a thermal viscoplastic model considering the combined effect of strain-rate and temperature is developed to describe the mechanical behavior of unstructured clay. By incorporating the bonding degradation, the model is extended that can be suitable for structured clay. The extended model is used to simulate CRS (Constant Rate of Strain) tests conducted on structural Berthierville clay with different strain-rates and temperatures. The comparisons between predicted and experimental results show that the extended model can reasonably describe the effect of bonding degradation on the stain-rate and temperature dependent behavior of soft structural clay under 1D condition. Although the model is proposed for 1D analysis, it can be a good base for developing a more general 3D model.

• 한국결정성장학회지
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• 제17권1호
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• pp.11-17
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• 2007

The spherical NiZn ferrite particles were prepared by ultrasonic spray pyrolysis with mixed solution of aqueous metal nitrates. The NiZn ferrite particle was observed with nano-sized primary particles of about 10 nm or less before annealing which represented as paramagnetic behavior measured at 77 K and room temperature. The typical abnormal growth of primary particles like polyhedral primary particles was observed by annealing at 1273 K with Zn-concentration dependency. The XRD patterns showed good crystallinity of NiZn ferrite powder after annealing. In annealing process, the intra-particle sintering phenomenon was observed and the spherical particle morphology was collapsed at 1673 K. The saturation magnetization of NiZn ferrite powder for each annealing temperature was decreased with measuring temperature of $77{\sim}$300K.

• 한국전기전자재료학회논문지
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• 제14권6호
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• pp.466-469
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• 2001

In this paper, we evaluated the dielectric properties of XLPE sheet of 22kV power cable, XLPE/semiconductor and XLPE/water/semiconductor depended on electric field and temperature respectively. Dielectric properties and temperature dependency of XLPE sheet of 22kV power cable increase greatly with as temperature increase and have no effect on applied voltage. And we confirmed that tan$\delta$ values in the samples with semiconductor or water layers were higher than those in the samples without them.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.703-706
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• 1998

This paper presents an efficient substrate-bias generator(SBG)for low-power, high-density DRAM's The proposed SBG can supply stable voltage with switching the supply voltage of driving circuit, and it can substitude the small capacitance for the large capacitance. The charge pumping circuit of the SBG suffere no VT loss and is to be applicable to low-voltage DRAM's. Also it can reduce the power consumption to make VBB because of it's high pumping efficiency. Using biasing voltage with positive temperature coefficient, VBB level detecting circuit can detect constant value of VBB against temperature variation. VBB level during VBB maintaining period varies 0.19% and the power dissipation during this period is 0.16mw. Charge pumping circuit can make VBB level up to -1.47V using VCC-1.5V, and do charge pumping operation one and half faster than the conventional ones. The temperature dependency of the VBB level detecting circuit is 0.34%. Therefore the proposed SBG is expected to supply a stable VBB with less power consumption when it is used in low power DRAM's.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.39-43
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• 2001

In this paper, excess minority carrier distribution in drift and buffer layers and accumulated charges for PT IGST have been, for the first time, analytically expressed with different transient times, lifetimes and temperatures. Furthermore those parameters are also expressed with temperature to predict the transient response which are critical to the real operation. Active base region has been chosen to extract the temperature dependency of the device by including the buffer layer which is important but neglected due to the complexity up to now.

• 한국자동차공학회논문집
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• 제10권4호
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• pp.199-205
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• 2002

This paper presents a numerical technique to analyze wear life of automotive disk brake pad, where FFT-FEM method is adopted to determine the transient temperature distribution of the disk surface. A specimen ova frictional material is tested on a small scale brake dynamometer to find the dependency of the wear rate on temperature change, from which and the temperature analysis results, given the wear test mode, wear behavior of the pad material fur the vehicle can be predicted. Numerical examples show the predicted wear life of the vehicle coincides with the manufacture's recommended time interval for replacing the pads.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.940-944
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• 2003

With the increasing demand for plastic micro components, micro-/nano-molding using the mother stamper has received much attention. If the replication temperature is too high, the adhesion between the stamper and the polymer melt may deteriorate the surface quality of the replicated part, excessively wearing down the stamper. In this paper, an experimental method analyzes the temperature dependency of the anti-adhesion property between the actual stamper with patterns of sub-micrometer and the polymer melt. As a practical example, a correlation between the contact angle of the stamper and the surface quality of the molded substrates as a function of the replication temperature, respectively, was obtained quantitatively.

• Advances in materials Research
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• 제7권1호
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• pp.1-16
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• 2018

Thermal bifurcation buckling behavior of fully clamped Euler-Bernoulli nanobeam built of a through thickness functionally graded material is explored for the first time in the present paper. The variation of material properties of the FG nanobeam are graded along the thickness by a power-law form. Temperature dependency of the material constituents is also taken into consideration. Eringen's nonlocal elasticity model is employed to define the small-scale effects and long-range connections between the particles. The stability equations of the thermally induced FG nanobeam are derived via the principal of the minimum total potential energy and solved analytically for clamped boundary conditions, which lead for more accurate results. Moreover, the obtained buckling loads of FG nanobeam are validated with those existing works. Parametric studies are performed to examine the influences of various parameters such as power-law exponent, small scale effects and beam thickness on the critical thermal buckling load of the temperature-dependent FG nanobeams.