• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2001년도 춘계학술대회 논문집
• /
• pp.167-171
• /
• 2001

High temperature deformation behavior of Fe-28Al-5Cr alloy has been investigated known to show anomalous temperature dependence of yield strength. Specifically, the effect of Cr addition has been examined. A series of tensile and load relaxation tests have been carried out to obtain the flow behavior of Fe-28Al-5Cr alloy at the elevated temperatures. The flow curves have then been analyzed using the inelastic deformation theory recently proposed. Firstly, high temperature flow stress of iron aluminides can be resolved into internal stress and frictional stress. Secondly, the temperature corresponding to peak strength gets higher level at faster strain rate, which presumably due to the increased contribution of internal stress in observed flow stress. And thirdly, the alloying of Cr seems to cause solid-solution strengthening of frictional stress level and the elevation of 2nd order transition temperature. In this analogy, Fe-28Al-5Cr exhibits better strength especially at relatively higher temperature and lower strain rate than Fe-28Al.

• 대한기계학회논문집A
• /
• 제27권7호
• /
• pp.1152-1158
• /
• 2003

The mechanical behavior of a commercially pure titanium (CP-Ti) is investigated at high temperature Split Hopkinson Pressure Bar (SHPB) compression test with high strain-rate. Tests are performed over a temperature range from room temperature to 1000$^{\circ}C$ with interval of 200$^{\circ}C$ and a strain-rate range of 1900 ∼ 2000/sec. The true flow stress-true strain relations depending on temperature are achieved in these tests. For construction of constitutive equation from the true flow stress-true strain relation, parameters for the Johnson-Cook constitutive equation is determined. And the modified Johnson-Cook equation is used for investigation of behavior of flow stress in vicinity of recrystalization temperature. The Modified Johnson-Cook constitutive equation is more suitable in expressing the dynamic behavior of a CP-Ti at high temperature, i.e. about recrystalization temperature.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2004년도 제5회 압연심포지엄 신 시장 개척을 위한 압연기술
• /
• pp.145-152
• /
• 2004

The flow stress value was calculated by comparing predicted and measured roll force. Using basic on-line roll force model and logged mill data the flow stress equation of high strength steel for automobile was derived. The flow stress equation consists of the flow stress equation of carbon steel and flow stress factor calculated by neural network with input parameters not only carbon contents, strip temperature, strain, and strain rate, but also compositions such as Mn, p, Ti, Nb, and Mo. Using the flow stress equation and basic roll force model, precision roll force model of high strength steel for automobile was derived. Using test set of logged mill data the flow stress equation was verified.

• Journal of Applied Biological Chemistry
• /
• 제63권4호
• /
• pp.347-355
• /
• 2020

기상이변으로 인한 식물 스트레스를 평가하기 위해 토양과 식물에 적용할 수 있는 여러 센서가 개발되었다. 따라서 본 연구의 목적은 식물의 온도 스트레스를 평가하기 위해 다양한 센서를 사용하여 기후 및 토양 상태와 식물 반응을 모니터링하는 것이다. 식물 반응을 평가하기 위한 식물 센서로 식물 줄기의 전기전도도, sap flow rate를 모니터링하였다. 식물 줄기의 전기전도도는 물과 이온 수송을 포함한 식물의 생리적 활성을 반영한다. 완전히 자란 Brassica oleracea var. italica를 온도 20/15 ℃ (낮/밤), 16시간 광주기로 하여 대조구로 설정하였으며 저온 15/10 ℃ 및 고온 35/30 ℃에 노출시키면서 토양 및 식물 상태를 모니터링하였다. 식물 줄기의 전기전도도, sap flow rate는 낮에는 증가하고 밤에는 감소하였다. 저온 스트레스 하에서 Brassica oleracea var. italica 줄기의 전기전도도는 대조구보다 낮았고, 고온 스트레스 하에서는 대조구보다 높아 물과 이온 수송이 온도에 의해 영향을 받았음을 나타낸다. 그러나 엽록소 a와 b 함량은 저온 스트레스를 받은 잎에서 증가했고 고온 스트레스를 받은 잎에서는 대조구와 차이가 없었다. 잎의 프롤린 함량은 저온 스트레스에서는 대조구와 차이가 없는 반면, 고온 스트레스에서는 증가했다. 프롤린 합성은 환경 스트레스 하에서 식물의 방어 메커니즘으로 작용한다. 따라서 Brassica oleracea var. Italica는 저온보다 고온 스트레스에 더 민감한 것으로 판단된다.

• 한국정밀공학회지
• /
• 제16권1호통권94호
• /
• pp.238-245
• /
• 1999

For the optimal design of plasma facing components of a fusion reactor, thorough understanding of thermal behavior of high heat. nux components are required. The purpose of this research is to investigate the characteristics of heat flow and thermal stress in divertors which are exposed to high heat load varing with time and space-Numerical simulations of heat now and thermal stress for three types of diverter are performed using finite volume method and finite element method. Respectly, commercial FLUENT code are used in the heat flow simulation, and maximum surface temperature, temperature distribution and cooling rate are calculated. Commercial ABQUS code are used for calculating temperature distribution. thermal stress, strain and displacement. Through this computer simulation. design data for cooling system and Structural provided.

• 소성∙가공
• /
• 제22권8호
• /
• pp.450-455
• /
• 2013

In the current study, a new dynamic recrystallization model for predicting high temperature flow stress is developed based on a physical model and the mean field theory. In the model, the grain aggregate is assumed as a representative volume element to describe dynamic recrystallization. The flow stress and microstructure during dynamic recrystallization were calculated using three sub-models for work hardening, for nucleation and for growth. In the case of work hardening, a single parameter dislocation density model was used to calculate change of dislocation density and stress in the grains. For modeling nucleation, the nucleation criterion developed was based on the grain boundary bulge mechanism and a constant nucleation rate was assumed. Conventional rate theory was used for describing growth. The flow stress behavior of pure copper was investigated using the model and compared with experimental findings. Simulated results by cellular automata were used for validating the model.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1999년도 제3회 압연심포지엄 논문집 압연기술의 미래개척 (Exploitation of Future Rolling Technologies)
• /
• pp.366-372
• /
• 1999

The deformation behavior of commercial stainless steels under hot rolling conditions was investigated by means of hot compression tests performed in the temperature range 800$^{\circ}C$ to 1200$^{\circ}C$. The measured flow stress-strain curves were analyzed by using a simple flow stress model. It was found that the reference strength of stainless steels are much higher than that of carbon steel and that nitrogen and molybdenum alloying greatly increases flow stress of austenitic stainless steel. Ferritic and duplex stainless steel showed comparatively low flow stresses. The flow stress model, which correlates the flow stress with temperature and strain rate, was applied to predict roll forces during hot-plate rolling of stainless steels.

• 한국기계가공학회지
• /
• 제10권3호
• /
• pp.67-72
• /
• 2011

Turbine blades operate under high temperature and pressure. The influence changes according to its width and angle. Thermal stress and pressure are important factors to analyze the stress distribution. The purpose of this study is to investigate the effects of loads on the gas turbine blade using thermal stress analysis. These analysis results show the gas fluid flow with a high pressure around the surface of blade. Gas temperature is related to the pressure of flow around the blade. The stress concentration around blade is shown and the concentration is due to the difference between suction side and pressure side of combustion gas.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 1999년도 춘계 학술대회논문집
• /
• pp.192-198
• /
• 1999

The present study proposes modified temperature-dependent non-Newtonian viscosity model and investigates flow characters and heat transfer enhancement of the viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. The proposed modified temperature dependent viscosity model has non-zero value near the high temperature and high shear rate region while on the existing viscosity models have zero value. Two versions of thermal boundary conditions involving difference combination of heated walls and adiabatic walls are analyzed in this study. The combined effect of temperature dependent viscosity, buoyancy, and secondary flow caused by second normal stress difference are ail considered. The Reiner-Rivlin model is adopted as a viscoelastic fluid model to simulate the secondary flow caused by second normal stress difference. Calculated Nusselt numbers by the modified temperature-dependent viscosity model gives under prediction than the existing temperature-dependent viscosity model in the regions of thermally developed with same secondary normal stress difference coefficients with experimental results in the regions of thermally developed. The heat transfer enhancement of the viscoelastic fluid in a 2:1 rectangular duct is highly dependent on the secondary flow caused by the magnitude of second normal stress difference.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
• /
• pp.69-72
• /
• 2002

The high temperature deformation behavior of SiCp/2124Al composite and 2124Al alloy was investigated by hot compression test in a temperature ranged $400~475^{\circ}C$ over a strain rate ranged $10^{-3}~1s^{-1}$. The billets of 2124Al alloy and SiCp/2124Al composite were fabricated by vacuum hot pressing process. The stress-strain curve during high temperature deformation exhibited a peak stress, and then the flow stress decreased gradually into a steady state stress with increasing the strain. It was found that the flow-softening behavior was attributed to the dynamic recovery, local dynamic recrystallization and dynamic precipitation during the deformation. The precipitation phases were identified as S' and S by TEM diffraction pattern. Base on the TEM inspection, the relationship between the Z-H parameter and subgrain size was found based on the experiment data. The dependence of flow stress on temperature and strain rate could be formulated well by a hyperbolic-sinusoidal relationship using the Zener-Hollomon parameter.