• Journal of the Korean Ceramic Society
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• v.29 no.11
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• pp.855-862
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• 1992

Thermoelectric power, electrical conductivity and Hall effect were measured, as functions of temperature in the range of 100 to 600 K, on polycrystalline Bi4/3Sb2/3Te3 which had been prepared via uniaxial hot-pressing at different temperatures in the range of 373 K to 773 K, aiming at searching a profitable processing route to a polycrystalline thermoelectric material, a promising, viable alternative to a single crystalline one. It was found that, with increasing temperature of pressing under a fixed pressure, the material, normally a p-type prior to being hot-pressed, underwent a transition to n-type. This transition was confirmed to be due to plastic deformation during hot-pressing and interpreted as being attributed to the change of the major ionic defect BiTe' into TeBi˙at temperature high enough for structure elements mobility. Thermoelectric figure-of-merit of the hot-pressed material was discussed in connection with the p-n transition in addition to microstructure.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.666-669
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• 2002

Process design of hot forging, asymmetric to symmetric rail, which is used for the turnout of railway express has been investigated. Owing to the big difference in shape between the initial billet and the final forged product, it is impossible to hot forge the rail in a single step. Therefore, multi step forging as well as die design for each step are necessary for the production. The deformation behavior during hot forging has been analyzed by the numerical simulation through commercial FEA software, DEFORM$^{TM}$-2D. Modification of the design and repeated simulation have been carried out on the basis of the simulation result. For comparison with the simulation results, flow analysis experiment using plasticize has been also carried out. The results of the flow analysis experiment showed good agreement with those of the simulation. Therefore, the developed process design could be applied to the actual production.

• Transactions of Materials Processing
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• v.11 no.3
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• pp.211-216
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• 2002

The mechanical and thermal load, and thermal softening occuring by the rush temperature of die, in warm and hot forging, cause wear, heat cracking and plastic deformation, etc. This paper describes the effects of solid lubricants and surface treatments for warm forging die. Because cooling effect and low friction are essential to the long life of dies, optimal surface treatments and lubricants are very important to hot and warm forging process. The main factors affecting die hardness and heat transfer, are surface treatments and lubricants, which are related to heat transfer coefficient, etc. To verify the effects, experiments are performed for heat transfer coefficient in various conditions - different initial billet temperatures and different loads. Carbonitriding and ionitriding are used as surface treatments, and oil-base and water-base graphite lubricants are used. The effects of lubricant and surface treatment for warm and hot forging die life are explained by their thermal characteristics, and the new developed technique in this study for predicting tool life can give more feasible means to improve the tool life in hot forging process.

• Transactions of Materials Processing
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• v.15 no.2 s.83
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• pp.143-147
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• 2006

Effect of processing condition on the hot extrusion of Al-Zn-Mg-Sc alloy was investigated. For this purpose, hot compression test and FE-simulation were conducted via Thermecmaster-Z and DEFORM-3D, respectively. The microstructure evolution during hot extrusion and post heat-treatment was investigated and deformation mechanisms were analyzed by constructing processing map. FE-simulation results show that the temperature difference between container and billet has considerable influence on the final shape of extruded T-shape bar. The relation between applied load and processing time was predicted by the FE-analysis as well as punch speed vs. stroke chart.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.202-205
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• 2005

Effect of processing condition on the hot extrusion of Al-Zn-Mg-Sc alloy was investigated. For this purpose, hot compression test and FE-simulation were conducted via Thermecmasteer-Z and DEFORM-3D, respectively. The microstructure evolution during hot extrusion and post heat-treatment was investigated and deformation mechanisms were analyzed by constructing processing map. FE-simulation results show that the temperature difference between container and billet has considerable influence on the final shape of extruded T-shape bar. The relation between applied load and processing time was predicted by the FE-analysis as well as punch speed vs. stroke chart.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.846-847
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• 2006

The composite used in this paper was prepared by hot-pressing ball-milled Mg alloy powders, in which NiTi shape memory alloy fibers in a row were sandwiched. The microstructure and property were examined. It is shown that the composite consisted of a homogenous matrix with uniformly distributed NiTi shape memory alloy fibers, recrystallization took place in the Mg alloy matrix which was subjected to plastic deformation an adequate bonding formed between the matrix and fibers; the density and tensile strength of the composite increased after the hot-forging; the hot-forging process is capable of improving properties of the composite.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.8
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• pp.3100-3105
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• 2010

The permanent deformation of asphalt pavement is one of the most important load-related distresses in asphalt pavement. In order to evaluate the permanent deformation, the repeated triaxial load test with different temperature and air void of hot mix asphalt was carried out. The permanent deformation prediction model has been validated by the multiple regression approach and the artificial neural networks.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1996.03b
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• pp.48-54
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• 1996

The continuous deformation , multistage deformation and stress relaxation were carried out to investigate the strain induced procipitation by torsion tests in the range of 1000∼800$^{\circ}C$, 0.05/sec∼5/sec for V-microalloyed steel. The starting temperature and time for the initiation of precipitation were determined by stress relaxation tests and the distribution of percipitates increased at higher strain rate and the mean size of precipitates was found to be about 50nm. The precipitation starting time decreased with increasing strain rate from 0.05/sec to 5 /sec and pre-strain. The effect of deformation conditions on the no-recrystallization temperature(Tnr) was determined in the multistage deformation with declining temerature. The Tnr decreased with increasing strain and strain rae. In the controlled rolling, grain refinement and precpitation hardening effects could be achieved by the alternative large pass strain at the latter half pass stage under the condition of low temperature and high strain rate.

• Transactions of Materials Processing
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• v.9 no.1
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• pp.80-87
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• 2000

The static softening behavior of SCM 440 could be characterized by the hot torsion test in the temperature ranges of 90$0^{\circ}C$~110$0^{\circ}C$and strain rate ranges of 0.05/sec~5/sec. Interrupted deformation was performed with 2 pass deformation in the pass strain ranges of 0.25$\varepsilon$p~3$\varepsilon$p and interrupted time ranges of 0.5~100sec. The dependences of process variables, pass strain ($\varepsilon$i), stain rate ($\varepsilon$), temperature (T) and interpass time (ti), on static recrystallization (SRX) and metadynamic recrystallization (MDRX)were individually predicted from the modified Avrami's equations, The dependence of pass strain on MDRX was neglectable. Comparison of the softening kinetics between MDRX and SRX showed that the rate of MDRX was more rapid than that of SRX for the same deformation variables. Controlled multipass deformations were performed using static and metadynamic recrystallization of SCM 440.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.5
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• pp.544-549
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• 2009

Thermal brake judder caused by the high friction heat of the brake disk. Hot thermal judder makes serious problems such as to be unstability to drivers or to decrease braking force of automobile. Because thermal judder vibration makes high vibration occurrence and thermal deformation of brake disk. Therefore it Is necessary to reduce or eleminate thermal Judder phenomenon by understanding and investigation. This paper introduces the thermal deformation arising from friction heat generation in braking and proposes the FEM analysis to predict the distribution of temperature and thermal deformation. the results of the FEM analysis show the deformed shape and temperature distribution of the disk brake. The optimization is performed to minimize the thermal judder of ventilated disc brake that is induced by the thermal deformation of the disk brake.