• 설비공학논문집
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• 제13권3호
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• pp.194-199
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• 2001

The turbulent flow resistance of water solution with polymer is reduced as compared with that of pure water. This effects is named th drag reduction and offers the significant reduction of the pumping power and the energy consumption. But the intense shear forces and the high temperature experienced by the polymer solution when passing through the pipes cause the degradation a loss of drag reduction effectiveness. Especially, the degradation behavior is found to be strongly dependent on temperature. This mechanical and thermal degradation can be avoided by adding materials such as surfactant to the polymer solution, which enhance the bonding force between molecules. In the present study, Copolymer and SDS were utilized and they were mixed in 10 different mixture ratios, while total concentration was fixed as 100wppm. Degradation of Copolymer-SDS mixture solutions was investigated experimentally in closed loop at the temperature of $10^{\circ}C\; and\; 80^{\circ}C$ with various flow average velocities of 1.5 m/sec, 3.0m/sec, and 4.5m/sec. Degradation characteristics of polymer solution without surfactant show a radical loss of drag reduction effectiveness at high temperature. Degradation alleviation ability of surfactant is especially effective at high temperature. Consequently, this results show that the addition of surfactant to the polymer solution can control unfavorable degradation phenomena for high temperature systems.

• 한국재료학회지
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• 제16권5호
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• pp.318-322
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• 2006

Short-term high temperature degradation test was conducted on Hastelloy X, a candidate tube material for high temperature gas-cooled reactors (HTGR), to evaluate the variation of microstructure and mechanical property in air at $1050^{\circ}C$ during 2000 h. The dominant oxide layer was Cr-oxide and a very shallow Cr-depleted region was observed below the oxide layer. At the beginning of degradation, the island shape $M_6C$ precipitate (M=Mo-rich, Fe, Ni, Cr) was observed in matrix region. After 2000 h degradation, precipitate shape was changed to the chain shape and increased amount of precipitate. These results influenced mechanical property of the specimen which exposed in high temperature. Yield strength was decreased from 115MPa to 89 MPa after 24 h and 2000 h exposure, respectively.

• 한국세라믹학회지
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• 제34권9호
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• pp.915-920
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• 1997

Tetragonal ZrO2 polycrystal (TZP), consisted of 90.24 mol% ZrO2-5.31 mol% Y2O3-4.45 mol% Nb2O5, were prepared using hot-press and mechanical properties and high-temperature degradation were investigated. The specimen, hot-pressed for 1 h at 140$0^{\circ}C$ in Ar atmosphere, exhibited flexural strength of 1010 MPa and fracture toughness of 7.5 MPam1/2 and experienced no low-temperature degradation below 40$0^{\circ}C$. However, as aged for 100h at temperatures higher than 40$0^{\circ}C$, TZP was suffered by high-temperature degradation due to an extensive cavitation caused by the oxidation of carbon. XPS observation revealed that the carbon incorporated in TZPs during hot-pressing exists as either an ether-type CO or a carbonyl-type C=O. Despite of the high-temperature degradation of t-ZrO2 co-doped with Y2O3 and Nb2O5, its flexural strength and fracture toughness were superior to those of the commercial 3 mol% Y2O3-TZP hot-pressed under the identical condition as determined before and after the aging treatments.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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• pp.26-27
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• 2014

Study on high temperature properties of concrete and internal force estimation of structural member subjected to high temperature mainly applied high temperature strength model based on experimental results with concrete under 40MPa. However, it is reported that degradation of internal force at high temperature and spalling of ultra high strength concrete are higher than that of normal strength concrete. Therefore, this study attempts to propose compressive strength degradation model which is suitable to ultra high strength concrete comparing to existing model by evaluating high temperature properties of ultra high strength concrete.

• 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.

• 한국신뢰성학회지:신뢰성응용연구
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• 제17권1호
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• pp.22-27
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• 2017

Purpose: The purpose of this study is to estimate the life time of OLED TV panel through electric current ADT(Accelerated Degradation Test). Methods: We performed accelerated degradation test for OLED TV Panel at the room temperature to avoid high temperature impact on the luminance. Results: we got more accurately the life time of the OLED TV when we applied ADT without temperature factor than including both current and temperature. Conclusion: Until now, the ADT of the OLED TV has been conducted with temperature and current at the same time for reducing test time and costs. We estimate incorrect life time when the temperature is adopted as an accelerated factor. Due to the high temperature impact on the luminance of the OLED TV panel. So as to solve this problem, we discard temperature and use electric current only.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1123-1132
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• 1996

It has been reported that high temperature structural components represent the phenomenon of material degradation according to a long term service under high temperature and pressure. Especially, fossile power plant components using the fossil fuel and heavy oil are affected by dewpoint corrosion of $H_2SO_4$produced during a combustion. Therefore, the service materials subjected to high temperature and pressure may occur the stress corrosion cracking. The object of this paper is to investigate SCC susceptibility according to the material degradation of the high temperature structural materials in dewpoint corrosive environment-$H_2SO_4$.The obtained results are summarized as follows : 1) In case of secondary superheater tube, the fractograph of dimple is observed at the concentration of $H_2SO_4$-5%. When the concentration of $H_2SO_4$ is above 10%, the fracture mode is shifted from a transgranular fracture to an quasi-intergranular fracture according to the increment of concentration. 2) In the relationship between [$\Delta$DBTT]$_sp$ and SCC susceptibility, it is confirmed that the greater material degradation degree is, the higher SCC susceptibility is. In addition, it can be known that SP test is useful test method to evaluate SCC susceptibility for high temperature structural components. 3) When [$\Delta$DBTT]$_sp$ is above 17$17^{\circ}C$ the SCC fracture behavior is definitely observed with SCC susceptibility of above 0.4.

• 대한기계학회논문집A
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• 제31권3호
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• pp.295-303
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• 2007

Degradation behaviors of filament-winded composites have been evaluated under the accelerated environmental test of high temperature, water immersion and thermal impact conditions. Two kinds of laminated composites coated by an urethane resin have been used: carbon-fiber reinforced epoxy(T700/Epon-826, CFRP) and glass-fiber reinforced phenolic (E-glass/phenolic, GFRP). For tensile strength of $0^{\circ}$ composites, CFRP showed little degradation while GFRP did high reduction by 25% under the influence of high temperature and water However for water-immersed $90^{\circ}$ composites tensile strength of both CFRP and GFRP showed high reduction. Bending strength and modulus of $90^{\circ}$ composites were largely reduced in water-immersion as well as high temperature environment. Urethane coating on the composite surface improved the bending properties by 20%, however hardly showed such improvement for water-immersed $90^{\circ}$ composites. In case of shear strength and modulus, both CFRP and GFRP showed high reduction by water-Immersion test but did a slight increase by high temperature and thermal impact conditions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.268-273
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• 2001

Fossil power plants operated in high temperature condition are composed of components such as turbine, boiler, and piping system. Among these components, turbine blades made with 12%Cr steel operate at a temperature above $500^{\circ}C$. Due to the long term service, turbine blades experience material degradation manifested by change in mechanical and microstructural properties. The need to make life assessment and to evaluate material degradation of turbine blade is strongly required but in reality, there is a lack of knowledge in defining failure mechanism and fundamental data for this component. Therefore, in making life assessment of turbine blade, evaluation of material degradation must be a priority. For this purpose, evaluation of toughness degradation is very important. The major cause of toughness degradation in 12Cr turbine blade is reported to be critical corrosion pitting induced by segregation of impurity elements(P etc.), coarsening of carbide, and corrosion, but the of materials for in-service application. In this study, the purpose of research is focused on evaluating toughness degradation with respect to operation time for 12%Cr steel turbine blade under high temperature steam environment and quantitatively detecting the degradation properties which is the cause of toughness degradation by means of non-destructive method, electrochemical polarization.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.321-324
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• 2009

Upgrading of pyrolysis wax oil has been conducted in a continuous fixed bed reactor at $450^{\circ}C$, 1hour, LHSV 3.5/h. The catalytic degradation using HZSM-5 catalyst are compared with the thermal degradation and also was studied with a function of experimental variables. The raw pyrolysis wax oil shows relatively high boiling point distribution ranging from around $300^{\circ}C$ to $550^{\circ}C$, which has considerably higher boiling point distribution than that of commercial diesel. The product characteristic from thermal degradation shows a similar trend with that of raw pyrolysis wax oil. This means the thermal degradation of pyrolysis wax oil at high degradation temperature is not sufficiently occurred. On the other hand, the catalytic degradation using HZSM-5 catalyst relative to the thermal degradation shows the high conversion of pyrolysis wax oil to light hydrocarbons. This liquid product shows high gasoline range fraction as around 90% fraction and considerably high aromatic fraction in liquid product. Also, in the catalytic degradation the experimental variable such as catalyst amount and reaction temperature was studied.