• Korean Journal of Materials Research
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• v.4 no.5
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• pp.524-534
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• 1994

The effects of transformation temperature and mechanical properties by thermal cycle of CuZnAl shape memory alloy with a small of misch metal and Zr contents were investigated. The addition of misch metal and Zr was very effective for reducing the grain size. After solution treatment, the specimens were post-quench aged or step quenched at $100^{\circ}C$ to $350^{\circ}C$ for variation of Rockwell hardness value. It was found that the Rockwell hareness value was very increased at $200^{\circ}C$ and $250^{\circ}C$. The fracture strength and ductility have been significantly increased with the increase of misch metal conten when tensile tested below $M_f$ temperature. Also, the fracture strength has been more increased in the case of post quench aging treatment than that of the as-quenching treatment. Aging of the $\beta$-phase decreases the $M_s$ temperature, but that of the martensite phase increases the $A_s$ temperature. The change in $A_s$ temperature with post-quench aging can be attributed to recovery of order in the $\beta$phase. The hystersis of transformation temperature ($A_s-M_s$) has an increasing tendency by thermal cycles.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1219-1226
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• 2000

An efficient method is developed for plunger thermal cycle analysis in repeated forming process of the TV glass. The plunger undergoes temperature fluctuation during a cycle due to the repeated contact and separation from the glass, which attains a cyclic steady state having same temperature history at every cycle. Straightforward analysis of this problem brings about more than 80 cycles to get reasonable solution, and yet hard to setup stopping criteria due to extremely slow convergence. An exponential fitting method is proposed to overcome the difficulty, which finds exponential function to best approximate temperature values of 3 consecutive cycles, and new cycle is restarted with the fitted value at infinite time. Numerical implementation shows that it reduces the number of cycles dramatically to only 6-18 cycles to reach convergence within 10 accuracy. A system for the analysis is constructed, in which the thermal analysis is performed by commercial software ANSYS, and the fitting of the result is done by IMSL library. From the parametric studies, one reveals some important facts that although the plunger cooling or the glass thickness is increased, its counter part in contact is not much affected, duo to the low thermal conductance of the glass.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.192-198
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• 2000

Three dimensional thermal cycle analysis of the plunger is carried out in repeated forming process of the TV glass, which is continued work of two dimensional analysis where an efficient method has been proposed. The plunger undergoes temperature fluctuation during a cycle due to the repeated contact and separation from the glass, which attains a cyclic steady state having same temperature history at every cycle. Straightforward analysis of this problem brings about more than 90 cycles to get reasonable solution. An exponential function fitting method is proposed, which finds exponential function to best approximate temperature values of 3 consecutive cycles, and new cycle is restarted with the fitted value at infinite time. Number of cases are analyzed using the proposed method and compared to the result of straightforward repetition, from which one finds that the method always reaches nearly convergent solution within $9{\sim}12$ cycles, but turns around afterwards without further convergence. Two step use is found most efficient, in which the exponential fitting is carried out fer the first 12 cycles, followed by simple repetition, which shows fast convergence expending only 6 additional cycles to get the accuracy within 2 error. This reduces the computation cycle remarkably from 90 to 18, which is 80% reduction. From the parametric studies, one reveals that the overall thermal behavior of the plunger in terms of cooling parameters and time is similar to that of 2 dimensional analysis.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.5
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• pp.349-357
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• 2015

The piezoelectric paint sensor is a paint type sensor comprising of an epoxy and piezoelectric powder, which is the main component of a piezoelectric material. This sensor can be easily attached to any type of structure as compared to other sensors because it is viable to directly apply it on structures, as in the case with a typical paint. In this study, the capability of piezoelectric paint sensor for impact detection was evaluated. In Particular, the applications of the piezoelectric paint sensor for railroad vehicles were considered. There have been various cases reported about the damages caused by flying gravel to the under-cover of the railroad vehicle during operation. In order to prevent this, real-time monitoring of the large under-cover surface of the railroad vehicle is unavoidable. Under the assumption of vehicle application, sensor sensitivities were measured after multiple and prolonged exposure to thermal cycle environment $-20{\sim}60^{\circ}C$). Sensitivity evaluation of paint sensor under environmental conditions was conducted in an aluminum specimen. In results, despite the small variations in sensitivity, we could confirm the applicability of this paint sensor for impact detection even after a severe environmental exposure test.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.2
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• pp.175-181
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• 2011

The purpose of this study is to secure the design data for the optimization of the radial turbine and heat cycle system, by using the CFD analysis technique and the design of 100kW class radial turbine applicable to waste heat recovery generation system for ship. Radial turbine was comprised of scroll casing, vane nozzle with 18 blades and rotor with 13 blades, and analysis grid was used to about 2.3 million. Mass flow rate and rotational speed was 0.5kg/s, 75,0000rpm, respectively. Eight kinds of inlet pressure was set between 195 and 620kPa. As the flow accelerated through the nozzle passage to the throat, the pressure level at the pressure and suction sides becomed similar to about Mach number of 0.35. When the inlet temperature and pressure was $250^{\circ}C$, 352kPa respectively, the isentropic efficiency and mechanical power showed the analysis results of 74% and 108kW.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.43-48
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• 2000

Composite materials have been increasingly used in automotive and aircraft industries, naturally leading to active researches on the materials. The carbon-epoxy composite is selected to study its thermal characteristics. During multiple thermal cycles composed of repeated cooling and heating variations of elastic constants are investigated to understand thermal effects on the carbon-epoxy composite. In this investigation longitudinal resonance method and flexural resonance method was used to characterize. The values of $E_1$ show small amount of increases depending on number of cycles of the thermal fatigue processes whereas values of $G_13$ do not indicate noticeable changes. Also, in cases of $E_2$ and $G_23$ their values decrease to a certain extend in initial stages after applications of thermal fatigue processes. However, the number of cycles of the applied thermal fatigue processes does not seem to affect their values.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.265-269
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• 2003

Sn(또는 SnAg)/Ni(P)와 Sn/Cu 계의 열사이클동안 형성되는 금속간화합물에 의해 유기되는 응력의 변화를 in-situ로 관찰하였다. Sn(또는 SnAg)/Ni(11.7P) 박막은 계면반응으로 인해 $Ni_3P$와 $Ni_3Sn_4$ 상이 형성되고 이때 인장응력이 발생하였으며, 한편, Sn(또는 SnAg)/Ni(3P) 박막의 계면반응에 의해서는 동일한 $Ni_3P$와 $Ni_3Sn_4$ 상이 형성됨에도 불구하고 압축응력이 발생하였다. SmAg를 사용할 때 형성되는 $Ag_3Sn$이 응력에 미치는 영향은 거의 없었다. Sn/Cu 박막의 경우는 계면반응 초기에는 인장응력이 발생하였고 어느 정도 이상 반응이 진전됨에 따라 압축응력이 발생하였고 최종적으로 $Cu_3Sn$ 상이 형성되었다. 초기의 인장응력은 계면에서 원자들의 intermixing 베 의한 것이고 압축응력은 Sn 방향으로 일방향 성장하는 금속간화합물 형성에 기인한다.

• Journal of Welding and Joining
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• v.10 no.3
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• pp.26-39
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• 1992

Diffusion bonding of Mo was performed by using the metallic coating of Cu and Cr on the surface to be bonded. Joint characteristics of Mo with or without coating layer were compared in metallurgical and fractograpical aspects. The results showed that the diffusion bonding with coating layer, especially with Cu coating, increased the bending strength of joint. Variation of heating cycle(elevation of temperature for a moment) did not affect significantly the mechanical properties of joint. Fractographical analysis showed that the fracture of joint bonded with Cr coating occurred at the coating layer, while that with Cu coating occurred at the base metal.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.273-273
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• 2009

고체산화물 연료전지 (Solid Oxide Fuel Cell, 이하 SOFC)는 제조형태에 따라 크게 평판형과 원통형으로 구분할 수 있다. 단위면적당 출력 효율이 높은 평판형의 장점과 원통형의 밀봉이 용이한 장점을 동시에 가지는 평관형 형태로 지지체를 제작하였으며, 셀의 배치를 평면상 직렬로 연결하는 다전지식으로 구성함으로 전극의 길이나, 셀 간격을 기존 평판형이나 원통형에 비해 대폭 감소시켜 단위면적당 전압 및 출력효율을 높이고자 하였다. Segmented 평관형 지지체의 소재로는 연료전지의 성능 특성에 관여하지 않으며 열사이클 저항성과 기계적 강도가 우수한 spinel구조를 가지는 $MgAl_2O_4$를 선정하였다. 연료가스의 원활한 공급이 가능하도록 carbon을 기공 전구체로 사용하여 압출성형하였으며 건조과정에서 crack이 생기지 않는 공정을 확립한 후 $1400^{\circ}C$ 에서 소결하였다. 제조된 지지체는 수은침투법과 3점 굽힘 강도법으로 기공율과 기계적 강도를 각각 측정하였다. Anode를 스크린 프린팅법으로 지지체 위에 적층한 후 미세구조를 확인하였고 이를 바탕으로 다공성이며 기계적 강도를 가지고 음극과의 반응이 없는 우수한 지지체를 제조할 수 있었다.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1312-1314
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• 1998

SOFC system is often subject to thermal cycle condition during normal start/stop, shutdown, and emergence state. Under the thermal cycle condition of heating and cooling, the SOFC components expand or shrink, which produces thermal stress and thermal shock. The SOFC performance is degraded by the thermal factors. To protect SOFC system from the thermal degradation, the optimum thermal condition must be clarified. In this study, to examine the thermal cycle characteristics, we fabricated single cells of planar SOFC with an area of $5{\times}5cm$. The electrolyte and PEN were tested under thermal cycle conditions in the range of$ 2-8^{\circ}C/min$. After thermal cycle test. crack creation of the components were examined using ultraviolet apparatus. No crack in the electrolyte and PEN were observed. The single cell system with alumina frame were also tested under thermal cycle conditions of 2, 3, $4^{\circ}C/min$. The single cell was fractured at the thermal cycle of 3 and $4^{\circ}C/min$ and the optimum condition of the thermal cycle to be found below $2^{\circ}C/min$.