• Composites Research
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• 제30권1호
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• pp.7-14
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• 2017

In this paper, the inter-lamina shear strength (ILSS) of multi-wall carbon nanotube (MWNT) reinforced carbon fiber reinforced plastics (CFRP) and thin-ply composites were verified under low earth orbit (LEO) space environment. CFRP, MWNT reinforced CFRP, thin-ply CFRP and MWNT reinforced thin-ply CFRP were tested after aging by using accelerated ground simulation equipment. The used ground simulation equipment can simulate high vacuum ($2.5{\times}10^{-6}torr$), atomic oxygen (AO, $9.15{\times}10^{14}atoms/cm^2{\cdot}s$), ultraviolet light (UV, 200 nm wave length) and thermal cycling ($-70{\sim}100^{\circ}C$) simultaneously. The duration of aging experiment was twenty hours, which is an equivalent duration to that of STS-4 space shuttle condition. After the aging experiment, ILSS were measured at room temperature ($27^{\circ}C$), high temperature ($100^{\circ}C$) and low temperature ($-100^{\circ}C$) to verify the effect of operation temperature. The MWNT and thin-ply shows good improvement of ILSS at ground condition especially with the thin-ply. And after LEO exposure large degradation of ILSS was observed at MWNT added composite due to the thermal cycle. And the degradation rate was much higher under the high temperature condition. But, at the low temperature condition, the ILSS was largely recovered due to the matrix toughening effect.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.219-224
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• 2000

A research for development of composite body panel is in progress for lightening tare. Low specific weight LPMC (Low pressure molding compound) has advantages such as lightweight and resistance to dent and corrosion. In this study, tensile, bending and impact tests for the LPMC and SPRC35 (High tension steel plate) were carried out and compared. Although mechanical properties of SPRC35 are better than the LPMC, the LPMC satisfies basic requirements for car body panel. The high temperature exposed LPMC were degraded due to fiber-matrix debonding and deterioration of resin.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.365-366
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• 2002

The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on a novel low temperature degradation-free zirconia/alumina composite material and conventional alumina and zirconia ceramics used for femoral head in total hip joint replacement. The wear of UHMWPE pins against these ceramic disks was evaluated by performing linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in bovine serum. The weight loss of polyethylene against the novel low temperature degradation-free zirconia/alumina composite disks was much less than those against conventional ceramics for all tests. The mean weight loss of the polyethylene pins was more io the linear reciprocal sliding test than in the repeal pass rotational sliding lest for all kinds of disk materials. Neither the coherent transfer film nor the surface damage was observed on the surface of the novel zirconia/alumina composite disks during the test. The observed r,'stilts indicated that the wear of the polyethylene was closely related to contacting materials and kinematic motions. In conclusion, the novel zirconia/alumina composite leads the least wear of polyethylene among the tested ceramics and demonstrates the potential as lhe alternative materials for femoral head in total hip joint replacement.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.355-361
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• 2004

Ceramic femoral heads in the total hip replacement have been developed to reduce the polyethylene liner wear, Alumina and zirconia (3Y-TZP) having the excellent tribological properties are coupled against acetabular cups of polyethylene and are used in clinical application worldwide. However, alumina has a risk of catastrophic failure, and zirconia has the low temperature degradation in spite of enhanced fracture toughness. Recently, novel zirconia/alumina composite is very attractive due to the low temperature degradation (LTD)-free character and high fracture toughness. In the present study, we focus on the wear of ceramic on ceramic, which are able to be used as femoral heads and acetabular cups. Therefore, LTD-free zirconia/alumina composites with three compositions are made in a form of disk and cylinder, and the wear of the composites is performed on pin-on-disk type wear tester. The wear is conducted with or without lubricant. All the composites fabricated with the different composition show the good wear resistance.

• 에너지공학
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• 제7권2호
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• pp.163-171
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• 1998

고분자 첨가물의 퇴화는 시험용액의 고온상태에서 증가된다. 합성고분자용액의 퇴화에 대해 시간에 따른 온도와 고분자 농도의 영향을 알아보기 위해 6$0^{\circ}C$, 8$0^{\circ}C$의 온도와 100, 200, 400, 600 ppm의 다양한 고분자 농도에 따라 폐회로방식으로 실험적인 연구를 하였다. 퇴화효과는 기계적 퇴화보다 온도에 더 의존적임이 밝혀졌다. 마찰계수와 레이놀즈 수의 관계는 레이놀즈 수가 5만부터 15만까지의 범위에서 레이놀즈 수가 증가함에 따라 마찰계수가 감소하고, 저온에서 마찰은 Vi가의 최대마찰저항감소 점근선에 접근한다는 것을 보인다. 일정한 유량과 온도에 대해, 높은 고분자 농도에서 퇴화효과가 더 작게 밝혀졌다. 일정한 유량과 고분자 농도에 대해서는 퇴화율이 주로 온도에 영향받는 것으로 밝혀졌다. 8$0^{\circ}C$의 온도, 100 ppm의 고분자 농도에서 4시간후에 마찰저항 감소효과가 없어졌다. 그러나, 열적퇴화는 고분자 분자들간의 결합력을 증가시켜 주는 것으로 생각되는 계면활성제 같은 추가적인 물질을 이용하여 극복할 수 있을 것이다.

• 대한기계학회논문집A
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• 제30권8호
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• pp.965-975
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• 2006

High pressure turbine blades are one of the key components in fossil power plants operated at high temperature. The blade is usually made of 12Cr steel and its operating temperature is above $500^{\circ}C$. Long term service at this temperature causes material degradation accompanied by changes in microstructures and mechanical properties such as strength and toughness. Quantitative assessment of reduction of strength and toughness due to high temperature material degradation is required for residual life assessment of the blade components. Nondestructive technique is preferred. So far most of the research of this kind was conducted with low alloy steels such as carbon steel, 1.25Cr0.5Mo steel or 2.25Cr1Mo steel. High alloy steel was not investigated. In this study one of the high Cr steel, 12Cr steel, was selected for high temperature material degradation. Electrochemical polarization method was employed to measure degradation. Strength reduction of the 12Cr steel was represented by hardness and toughness reduction was represented by change of transition temperature, FATT. Empirical relationships between the electrochemical polarization parameter and significance of material degradation were established. These relationship can be used for assessing the strength and toughness on the aged high pressure blade components indirectly by using the electrochemical method.

• 신재생에너지
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• 제17권1호
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• pp.19-32
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• 2021

Photovoltaic (PV) panels are generally treated as the most dependable components of PV systems; therefore, investigations are necessary to understand and emphasize the degradation of PV cells. In almost all specific deprivation models, humidity and temperature are the two major factors that are responsible for PV module degradation. However, even if the degradation mode of a PV module is determined, it is challenging to research them in practice. Long-term response experiments should thus be conducted to investigate the influences of the incidence, rates of change, and different degradation methods of PV modules on energy production; such models can help avoid lengthy experiments to investigate the degradation of PV panels under actual working conditions. From the review, it was found that the degradation rate of PV modules in climates where the annual average ambient temperature remained low was -1.05% to -1.16% per year, and the degree of deterioration of PV modules in climates with high average annual ambient temperatures was -1.35% to -1.46% per year; however, PV manufacturers currently claim degradation rates of up to -0.5% per year.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.1254-1257
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• 2004

Comparative study on the effects of $H_2$ vs. $O_2$ plasma pretreatment of gate oxide on the degradation phenomenon of p-channel low-temperature polysilicon (LTPS) thin-film transistors (TFTs) were performed. After high drain current stress (HDCS) with $V_{gs}$ = $V_{ds}$, the p-channel TFTs pretreated by $O_2$ plasma showed increased immunity to the degradation of device characteristics such as threshold voltage and maximum field effect mobility because of the higher binding energy of Si-O bond than that of Si-H bond. The investigation of degradation phenomenon of these parameters with the applied power suggests that self-heating can be the major cause of degradation of polysilicon TFTs.

• 한국세라믹학회지
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• 제27권2호
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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.

• 한국전기전자재료학회논문지
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• 제17권12호
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• pp.1289-1295
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• 2004

In this paper, degradation in field-aged PV modules including degradation of interconnect, discoloration of encapsulant and hot spot have been observed and analyzed. From the results, photovoltaic module installed for 6 years shows around 16 % drop of electrical properties due to the interconnect degradation and PV module passed 18 years has been found to drop of around 20 % mainly by the encapsulant discoloration. Furthermore the difference between low and high temperature of PV array at hot spot goes up to 3$0^{\circ}C$ and it leads to interconnect degradation. On the other hands, the temperature difference was observed to be around 15$^{\circ}C$ at the encapsulant discoloration spot of PV array.