• Journal of Ocean Engineering and Technology
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• v.9 no.1
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• pp.101-110
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• 1995

In SMA(Shape Memory Alloy), the degradation by fatigue is one of the most important problems to be overcome, when SMA is used for robot-actuator materials. The actuator is operated repetitively for long time and its repeating operation develops the fatigue degradation of SMA. The fatigue degradation changes the transformation temperature and deformation behavior and results in inaccurate operation and deformation which results form repeating operation is to be investigated in advance and the scheme to resolve those problems have to be made for the design of actuator. In this paper, for the improvement of the fatigue degradation by repetive movement and better control of the correct movement by the stability of martensite transformation in the development of Robots actuator, Pre-strain(0, 1.5, 5, 8%) are loaded in the specimens and fatigue testing were carried out by the method of heating and cooling in direct condition. From the results of these experiments, the effect on pre-strain which affect the transformation characteristic and fatigue degradation phenomena were correctly investigated.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.166-169
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• 2017

This paper describes atmospheric phenomena and effects for satellite-to-ground laser communication channel. Satellite laser communication has advantages such as very high bandwidth, inherent security, robustness to electromagnetic interference, unlicensed frequency band. However, satellite laser communication is affected by various factors. Transmission quality is degraded by factors as system loss, geometric loss, misalignment loss, atmospheric loss. Atmospheric loss is major factor of performance degradation. In this paper, the atmospheric phenomena such as absorption, scattering and turbulence are discussed and analyzed for developing satellite laser channel model and laser transmission scheme robust to atmospheric phenomena.

• Proceedings of the Korean Ceranic Society Conference
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• 2000.04a
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• pp.137.2-137.2
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• 2000

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05c
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• pp.25-28
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• 2001

The objectives of this paper are to demonstrate the electrical degradation phenomena with Si atom's behaviors in the grainboundary of semiconducting ZnO ceramics. The ZnO ceramic devices used in this investigation were fabricated by standard ceramic techniques. Especially, $SiO_2$ were added to analyze the degradation characteristics with Si and sintered in oxygen ambient at $1300^{\circ}C$. The conditions of DC degradation test were $115{\pm}2^{\circ}C$ for 13h. Using XRD and SEM, the phase and microstructure of samples were analyzed respectively. E-J analysis was used to determine $\alpha$. Frequency analysis was accomplished to understand $R_g$ and $R_b$ at the equivalent circuit. Electrical stability improved as the amount of $SiO_2$ addition increased. This results were explain by the quantitative analysis and the line scanning method of EPMA.

• Journal of the Korean institute of surface engineering
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• v.50 no.5
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• pp.398-404
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• 2017

In order to study the AC driving mechanism for OLED lighting, the fluorescent OLEDs were fabricated and the electroluminescent characteristics of the OLEDs by AC forward bias were analyzed. In the case of the driving method of OLED by AC forward bias under the same voltage and the same current density, degradation of luminescent characteristics for elapsed time progressed faster than in the case of the driving method by DC bias. These phenomena were caused by the peak voltage of AC forward bias which is ${\sqrt{2}}$ times higher than the DC voltage. In addition, the degradation of the OLED was accelerated because the AC forward bias had come close to the upper limit of the allowable voltage range even though the peak voltage didn't exceed the allowable range of the OLED. However, the fabricated fluorescent OLED showed little degradation of OLED characteristics due to AC forward bias from 0 V to 6.04 V. Therefore, OLED lighting by AC driving will become commercialized if sufficient luminance is realized at a voltage at which the characteristics of the OLED are not degradation by the AC driving method.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.357-366
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• 2000

Longitudinal dynamic behaviors of a bridge system under seismic excitations are examined with various magnitudes of peak ground accelerations. The stiffness degradation due to abutment-soil interaction is considered in the bridge model which may play the major role upon the global dynamic characteristics. The idealized mechanical model for the whole ridge system is proposed by adopting the multiple-degree-of-freedom system which can consider components such as pounding phenomena friction at the movable supports rotational and translational motions of foundations and the nonlinear pier motions. The abutment-soil interaction is simulated by utilizing the one degree-of-freedom system with nonlinear spring. The stiffness degradation of the abutment-soil system is found to increase the relative displacement under moderate seismic excitations.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.2
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• pp.86-91
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• 1999

In order to analyse the degradation process of epoxy/glass fiber for outdoor condition, FRP laminate was exposed to the wavelength of ultraviolet rays and evaluated by comparing contact angle, surface resistivity, surface potential decay, and ESCA spectrum respectively. As irradiation energy are increased, the surface properties were steeply decreased in the range of 300[nm]. But the measured values within the scope of400[nm]∼440[nm] showed a increase as compared with the untreated ones. Also, fromthe result of ESCA spectrum, it was confirmed plenty of oxygen groups on the spot showing the maximum decrease of surface properties and the existence of ether groups on the surface of coloring phase. We can conclude that the degradation phenomena on the surface of epoxy composites are dominated by the induction of ester and carboxyl groups.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2005.10a
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• pp.360-367
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• 2005

PMMA has been used extensively worldwide as industrial and construction materials due to its excellent material properties. When PMMA is subject to thermal degradation, unit of monomers are detached from polymer chain and this phenomena is called unzip reaction. Therefore, PMMA thermally degrades into its monomer. Characteristics of thermal degradation of PMMA has been investigated using TGA in this research as a basic study for recovery of MMA.

• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.226-232
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• 1990

The degradation phenomena and thermal stability of 2.5Y-TZP at low-temperature were studied by means of XRD, Raman spectra and microstructural analysis. The degradation of heat-treated 2.5Y-TZP at 20$0^{\circ}C$-20hr in air was observed on the TZP surface, be caused by the cracks generated from tlongrightarrowm transformation, and the cracks was propagated inside the polycrystalline body. The ZrO2 grain boundaries and grains near the crack were revealed as if these were diffused and dissolved. And it was also observed mlongrightarrowt transformation as the degraded TZP was refired at 140$0^{\circ}C$, and it was thought to be the fact that the moisture in atmosphere during the aging process contributed to the degradation. The thermal stability of 2.5Y-TZP was improved dramatically with an addition of 3w/o CeO2 or a provision of high Y2O3 concentration on the TZP surface.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1442-1444
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• 1994

The short channel poly-Si TFT is important in aspect of transistor characteristics, packing density and aperture ratio. In this paper, we have reported the degradation phenomena of short channel poly-Si TFT's which had significantly degraded device parameters, such as threshold voltage shift and a great asymmetric degradation, due to gate and drain electrical stress. The reduced effective channel length and expanded depletion region may be the main reason of these significant device parameters.