• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.145-148
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• 2005

In this study, adaptation of two-way shape memory effect of SMA wire to the actuator is examined . Therefore the SMA characteristics which are training, material properties, response time at different thermal cycling rates are tested. During training, permanent deformation is accumulated till a certain number of cycle and then saturated. The amow1t of two-way strain is unchangeable over all cycle and the slope of strain(or stress)-temperature curve is slower as the increase of applied stress. The rate effect is observed resulted from the thermal distribution which heating profile differs from cooling as thermal cycling time. Using the estimated SMA properties, an experimental test for the simple smart wing is performed.

• The Korean Journal of Rheology
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• v.10 no.2
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• pp.106-112
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• 1998

항공기용 소재로 개발된 에폭시/탄소섬유 복합재료가 매트릭스의 유리전이온도에 육 박하는 온도주기를 경험할 때 발생하는 복합재료의 구조 및 물성변화를 실험과 모델링을 통 하여 연구하였다. 복합재료의 표준 경화온도인 177$^{\circ}C$에서 2시간 체류시킨후 냉각시키는 바 복 열주기는 복합재료를 취약하게 하여 결국 표면에서부터 미세크랙이발생한다는 것을 알수 있었다. 이러한 열주기에 따른 미세크랙 현상은 매트릭스의 분해반응이 발생할수 있는 유효 표면적을 증가시키고 크랙을 통하여 산소의투과를 용이하게 함으로서 산화반응을 가속화하 여 복합재료시편의 무게감소를 가속화시키는 것으로 판단된다. 특히 본 연구에서는 등온과 등속도 승온조건을 주기적으로 반복하는 열주기 조건을 해석하기 위하여 열주기 조건을 특 정온도에서의 등오시간으로 전환할 수 있는 e-quivalent cycle time(ECT)를 제안하였고 이 를 이용하여 열주기에 의한 복합재료 손상의 가속/감속 현상을 규명할수있었다.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.683-688
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• 2013

Candidate coating materials for re-usable metallic nuclear fuel crucibles, TaC, TiC, ZrC, $ZrO_2$, and $Y_2O_3$, were plasmasprayed onto a niobium substrate. The microstructure of the plasma-sprayed coatings and thermal cycling behavior were characterized, and U-Zr melt interaction studies were carried out. The TaC and $Y_2O_3$ coating layers had a uniform thickness, and high density with only a few small closed pores showing good consolidation, while the ZrC, TiC, and $ZrO_2$ coatings were not well consolidated with a considerable amount of porosity. Thermal cycling tests showed that the adhesion of the TiC, ZrC, and $ZrO_2$ coating layers with niobium was relatively weak compared to the TaC and $Y_2O_3$ coatings. The TaC and $Y_2O_3$ coatings had better cycling characteristics with no interconnected cracks. In the interaction studies, ZrC and $ZrO_2$ coated rods showed significant degradations after exposure to U-10 wt.% Zr melt at $1600^{\circ}C$ for 15 min., but TaC, TiC, and $Y_2O_3$ coatings showed good compatibility with U-Zr melt.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.9-18
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• 2016

The thermal and mechanical properties of fiber-reinforced cement-based composite for solar thermal energy storage were investigated in this paper. The effect of the addition of different cement-based materials to Ordinary Portland cement on the thermal and mechanical characteristics of fiber-reinforced composite was investigated. Experiments were performed to measure mechanical properties including compressive strength before and after thermal cycling and split tensile strength, and to measure thermal properties including thermal conductivity and specific heat. Test results showed that the residual compressive strength of mixtures with OPC and slag was greatest among cement-based composite. Thermal conductivity of mixtures including graphite was greater than that of any other mixtures, indicating favor of graphite for improving thermal transfer in terms of charging and discharging in thermal energy storage system. The addition of CSA or zirconium increased specific heat of fiber-reinforced cement-based composite. Test results of this study could be actually used for the design of thermal energy storage system in concentrating solar power plants.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.5
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• pp.434-439
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• 2008

Silver pastes as the outer electrodes have been prepared using Pb-free glass frits with different content of $Bi_2O_3$ and the effects of glass composition on the degradation behaviors of the Ag electrodes were investigated using the change of adhesion between Ag electrode and alumina substrate with thermal cycle stress. Low adhesion and high surface resistance were observed in Ag electrode using glass frit with a $Bi_2O_3$ content of 60 wt%, owing to the open microstructure formed at the firing temperature of $600^{\circ}C$. When the $Bi_2O_3$ was increased to 80 wt% in the glass frit, the Ag electrodes had a dense microstructure with high adhesion and a low surface resistance. Delamination of the Ag electrodes was a major failure mode under thermal cycle stress and this was attributed to residual stress due to the thermal expansion mismatch between the Ag electrode and the alumina substrate.

• Proceedings of the Materials Research Society of Korea Conference
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• 2000.11a
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• pp.89-89
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• 2000

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.414-420
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• 2017

The thermal characteristics of concrete fabricated with blast furnace slag were investigated in this paper. Test parameters included water-binder ratio and the content of furnace slag. Experimental program were performed to measure mechanical properties including compressive strength and split tensile strength under high-temperature thermal cycling, and to measure thermal properties including thermal conductivity and specific heat. Test results showed that the residual compressive strength of mixtures with blast furnace slag was greater than that of mixture without blast furnace slag. In addition, thermal conductivity of mixtures with blast furnace slag was greater than that of mixtures without blast furnace slag. It indicates that blast furnace slag was favorable for charging and discharging in thermal energy storage system. Test results of this study would be used to design concrete module system of thermal energy storage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.7
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• pp.799-804
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• 2011

A thermal cycling test was conducted on a chip resistor solder joint with real-time failure monitoring. In order to study the failure mechanism of the chip resistor solder joint during the test, the resistance between both ends of the resistor was monitored until the occurrence of failure. It was observed that the monitored resistance first fluctuated linearly according to the temperature change. The initial variation in the resistance occurred at the time during the cycle when there was a decrease in temperature. A more significant change in the resistance followed after a certain number of cycles, during the time when there was an increase in the temperature. In order to explain the failure patterns of the solder joint, a mechanism for the solder failure was suggested, and its validity was proved through FE simulations. Based on the explained failure mechanism, it was shown that prognostics for the solder failure can be implemented by monitoring the resistance change in a thermal cycle condition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1856-1863
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• 2004

In the last 50 years, lead-contained solder materials have been the most popular interconnect materials used in the electronics industry. Recently, lead-free solders are about to replace lead-contained solders for preventing environmental pollutions. However, the reliability of lead-free solders is not yet satisfactory. Several researchers reported that lead-contained solders have a good fatigue property. The others published that the lead-free solders have a longer thermal fatigue life. In this paper, the reason for the contradictory results published on the estimation of fatigue life of lead-free solder is investigated. In the present study, fatigue behavior of 63Sn37Pb, and two types of lead-free solder joints were compared using pseudo-power cycling testing method, which provides more realistic load cycling than chamber cycling method does. Pseudo-power cycling test was performed in various temperature ranges to evaluating the shear strain effect. A nonlinear finite element model was used to simulate the thermally induced visco-plastic deformation of solder ball joint in BGA packages. It was found that lead-free solder joints have a good fatigue property in the small temperature range condition. That condition induce small strain amplitude. However in the large temperature range condition, lead-contained solder joints have a longer fatigue life.

• Transactions of the Korean hydrogen and new energy society
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• v.1 no.1
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• pp.1-8
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• 1989

The hydriding kinetic mechanism and the change of the hydriding reaction rate of $MmNi_{4.5}Al_{0.5}$ during the thermally induced hydrogen absorption-desorption cycling are investigated. Comparison of the reaction rate data which are obtained by the pressure sweep method with the theoretical rate equations suggests that the hydriding rate controlling step has changed from the dissociative chemisorption of hydrogen molecules at the surface to the hydrogen diffusion through the hydride phase with the increase of the hydriding fraction. These hydriding kinetic mechanism is not changed during the cycling. However, the intrinsic hydriding reaction rate of $MmNi_{4.5}Al_{0.5}$ after 5500 cycles increases significantly comparing with the activated one. It is suggested that the change of the hydriding kinetic behavior due to intrinsic degradation of $MmNi_{4.5}Al_{0.5}$ can be interpreted as follows ; the formation of nickel cluster at the surface of the sample and the host metal atom exchange in bulk by thermal cycling.