• Title/Summary/Keyword: Aging Resistance

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A Study on the High Frequency Ultrasonic Attenuation Characterization in Artificially Aging Degraded 2.25Cr-1Mo Steel (2.25Cr-1Mo 강 인공 열화재의 고주파수 초음파 감쇠특성에 관한 연구)

  • Park, Ik-Keun;Park, Un-Su;Kim, Chung-Seok;Kim, Hyun-Mook;Kwun, Sook-In;Byeon, Jai-Won
    • Journal of the Korean Society for Nondestructive Testing
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    • v.21 no.4
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    • pp.439-445
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    • 2001
  • The destructive method is reliable and widely used lot the estimation of material degradation but, it have time-consuming and a great difficulty in preparing specimens from in-service industrial facilities. Therefore, the estimation of degraded structural materials used at high temperature by nondestructive evaluation such as electric resistance method, replica method, Barkhausen noise method, electro-chemical method and ultrasonic method are strongly desired. Ultrasonic nondestructive evaluation technique has been reported good to attain efficiency of measurement, high sensitivity of measurement, and rapidity and reliability of result interpretation. In this study, it was verified experimentally the feasibility of the evaluation of degraded 2.25Cr-1Mo steel specimens which were prepared by the isothermal aging heat treatment at $630^{\circ}C$ by high frequency longitudinal wave method investigating the change of attenuation coefficient by FFT analysis and wavelet transform. Because of carbide precipitation increase and spheroidization near grain boundary of microstructure to aging degradation, attenuation coefficient had a tendency to increase as degradation proceeded. It was identified possibly to evaluate degradation using the characteristics of high-frequency ultrasonics. Frequency dependence of ultrasonic attenuation coefficient to aging degradation appeared large, which made sure that attenuation coefficient is an important parameter for evaluation of aging degradation.

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Seismic Response Evaluation of Composite Steel-Concrete Box Girder Bridge according to Aging Effect of Piers (교각의 노후도 영향에 따른 강합성 상자형 거더교의 지진응답 평가)

  • Shin, Soobong;Hong, Ji-Yeong;Moon, Jiho;Song, Jong-Keol
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.33 no.5
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    • pp.319-329
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    • 2020
  • Among the bridges used in Korea, those that are more than 30 years old account for approximately 11% of the total bridges. Therefore, developing a seismic performance-evaluation method is necessary by considering the bridge age. Three composite steel-concrete box girder bridges with port, elastic-rubber, and lead-rubber bearings were selected, and a structural analysis model was developed using the OpenSEESs program. In this study, pier aging was reflected by the reduction in the area of the longitudinal and transverse rebars. Four conditions of 5%, 10%, 25%, and 50% in the degree of pier aging were used. As input earthquakes, 40 near-fault and far-field earthquakes were used, and the maximum displacement and maximum shear-force responses of the piers were obtained and compared. The result shows that as the aging degree increases, the pier strength decreases. Therefore, the pier displacement response increases. To analyze the effects of displacement response and shear resistance, displacement ratio Dratio and shear-force ratio Fratio were evaluated. The older the sample bridge is, the greater is the tendency of Dratio to increase and the smaller is the tendency of Fratio to decrease.

EFFECTS OF ALLOYING ELEMENTS ON VARIOUS PROPERTIES OF DENTAL SILVER-PALLADIUM ALLOYS (치과용(齒科用) 은(銀)-파라디움합금(合金)의 합금원소(合金元素)가 제성질(諸性質)에 미치는 영향(影響)에 관(關)한 연구(硏究))

  • Kim, Chun-Jin;Park, Nam-Soo
    • The Journal of Korean Academy of Prosthodontics
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    • v.22 no.1
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    • pp.95-108
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    • 1984
  • Even though the tarnishing and corrosion problems characteristic with dental silver-palladium alloy are not yet fully solved, it is recently widely used because of its low cost. However the effects of major alloying elements on the various properties of this system are not fully understood. The object of this research is to clarify the effects of In and Zn additives on the corrosion and tarnishing resistances and precipitation hardening behavior of this sytem, using electrodynamic polarization, immersion, and Vicker's microhardness test and X-ray diffraction and electron probe micro analysis methods. The obtained results were as follows: I. As indium content is increased, both the corrosion resistance in Cl-solution and microhardness are also increased while the tarnishing resistance is decreased. 2. As Zinc content is increased, the corrosion resistance is decreased, but tarnishing resistance is increased 3. At 70Ag-25Pd-2.5Zn-2.5In composition, the precipitation harding behavior was mot significant. The optimum aging temperature was $450^{\circ}C$ and the time was 2 hrs. The resulting specimen of this work carried 180VHN. 4. Under the heat treatment, the changes in the mechanical property are due to the changes in the shape and composition of dendrite matrix, namely, it is because of the precipitation hardening behavior which has been proved by electron probe micro analysis and optical microscopic finding.

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Gas Impermeability Enhancement of EFDM/Crosslinked IIR Blends (Crosslinked IIR의 블렌드비에 따른 EPDM의 내기체투과특성 향상)

  • Kim, Hyun-Jun;Jung, Il-Hyun;Hong, In-Kwon;Park, Jae-Woo
    • Elastomers and Composites
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    • v.33 no.3
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    • pp.193-200
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    • 1998
  • It is well known that EPDM(ethylene propylene diene monomer) rubber has inherently excellent resistance to the weathering, ozone, heat, cold and moisture, whereas crosslinked IIR (isobutylene isoprene divlnyl benzene terpolymer) shows proper resistance to the water and gas permeation. Various characteristics of EPDM blend with crosslinked IIR such as curing characteristics, mechanical properties, dispersion of minor component and gas impermeability were explored. The optimum curing time $(t_{90})$ examined with peroxide was decreased by adding small amount of crosslinked IIR to the EPDM rubber. Mechanical properties of blends such as tensile strength, hardness and elongation at break were enhanced by increasing EPDM content. These results might be explained with the affinity of carbon black to the EPDM rubber. On the other hand, the physical properties were not changed significantly after aging, and the increase of crosslinked IIR fraction caused the decrease of compression set to small rate. EPDM rubber shows different behavior with crosslinked IIR in oxygen permeability. By adding 30wt.% crosslinked IIR to the EPDM rubber, the resistance to the oxygen permeation was improved up to three times than that of pure EPDM rubber. Conclusively, EPDM blend containing 30wt.% crosslinked IIR might be commercially applied to the o-ring and electric parts because of its proper resistance to the weathering, ozone and oxygen permeability.

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Tracking Performance Test of Polymer Insulator with Salt Solution which is added Surface Active Agent (계면활성제가 첨가된 염수용액에 따른 폴리머 애자의 트래킹 성능 평가)

  • Cho, Han-Goo;Lee, Un-Yong;Han, Dong-Hee;Kang, Sung-Hwa;Choi, In-Hyuk;Lim, Kee-Joe
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.18 no.1
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    • pp.62-67
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    • 2005
  • Recently, polymer insulators that are used for high voltage applications have some advantages such as light weight, small size, vandalism resistance, hydrophobicity and easy making process. During outdoor service of polymer insulators, the surface of the insulating material is frequently subjected to moisture and contamination that lead to dry band arcing. Their tracking resistance, erosion resistance, end sealing and shed design are very important because dry band arcing causes degradation of polymer surface. Aging test to estimate life property of polymer insulator is executed through several international standard such as IEC 61109 and CEA tracking wheel test, but is not getting clear conclusion yet. There are two methods in the diagnosis method of polymer insulator such as off-line and on-line. The diagnosis methods in off-line are external condition analysis by the eye, contaminant analysis on surface, surface analysis, pollution withstand voltage test, power frequency flashover voltage test, lightning impulse flashover test, tensile fracture load test and flexural load test. Polymer material is also investigated it's tracking resistance by adding surface active agent in IEC 587. In this paper, the tracking performance of polymer insulator with salt solution which is added surface active agent. The diagnosis of insulator sample has been analyzed by leakage current and visual examination, STRI guide and thermal image camera.

Characteristics of electrically conductive adhesives filled with silver-coated copper

  • Nishikawa, Hiroshi;Terad, Nobuto;Miyake, Koich;Aoki, Akira;Takemoto, Tadashi
    • Proceedings of the KWS Conference
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    • 2009.11a
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    • pp.217-220
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    • 2009
  • Conductive adhesives have been investigated for use in microelectronics packaging as a lead-free solder substitute due to their advantages, such as low bonding temperature. However, high resistivity and poor mechanical behavior may be the limiting factors for the development of conductive adhesives. The metal fillers and the polymer resins provide electrical and mechanical interconnections between surface mount device components and a substrate. As metal fillers used in conductive adhesives, silver is the most commonly used due to its high conductivity and the stability. However the cost of conductive adhesives with silver fillers is much higher than usual lead-free solders and silver has poor electro-migration performance. So, copper can be a promising candidate for conductive filler metal due to its low resistivity and low cost, but oxidation causes this metal to lose its conductivity. In this study, electrically conductive adhesives (ECAs) using surface modified copper fillers were developed. Especially, in order to overcome the problem associated with the oxidation of copper, copper particles were coated with silver, and the silver-coated copper was tested as a filler metal. Especially the effect of silver coating on the electrical resistance just after curing and after aging was investigated. As a result, it was found that the electrical resistance of ECA with silver-coated copper filler was clearly lower and more stable than that of ECA with pure copper filler after curing process. And, during high temperature storage test, the degradation rate of electrical resistance for ECA with silver coated copper filler was quite slower than that for ECA with pure copper filler.

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Effect of Cobalt Contents on the Biocompatibility and Corrosion Properties of Fe-31Cr-27Ni-1.6Mo-1.5W-0.26N Alloy (Fe-31Cr-27Ni-1.6Mo-1.5W-0.26N계 초내식성 스테인리스강의 생체적합성 및 부식특성에 미치는 Co함량의 영향)

  • Jang, Soon Geun;Yoo, Young Ran;Nam, Hee Soo;Shim, Gyu Tae;Kim, Jung Gu;Kim, Young Sik
    • Korean Journal of Metals and Materials
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    • v.46 no.4
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    • pp.209-216
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    • 2008
  • Super austenitic stainless steels shows the high PRE (Pitting Resistance Equivalent) number and the good corrosion resistance. This work controlled the Co contents in Fe-31Cr-1.7Mo-27Ni-0.25N alloys to elucidate the effect of cobalt contents on the biocompatibility and corrosion resistance. Increasing Co contents, the hardness of the annealed alloys tends to be reduced. In aged alloys, cobalt decreased the increments of hardness by aging treatment. Cobalt decreased the critical pitting temperature (CPT) in 6% $FeCl_3$ + 1% HCl solution, but improved the anodic polarization behavior in Hanks' balanced salt solution and artificial saliva solution. Repassivation rate in artificial body solutions was improved by increasing cobalt contents, but didn't show the linear relationship to PRE number of the alloys. The experimental alloys showed the non-cytotoxicity because of its high corrosion resistance.

Theoretical Study of Effective Resistance Exercise for Sarcopenia

  • Lee Sang Hyun;Jeong Hwan Jong
    • International Journal of Internet, Broadcasting and Communication
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    • v.15 no.2
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    • pp.187-195
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    • 2023
  • Sarcopenia is a phenomenon in which muscle function, including muscle strength, deteriorates as muscle mass decreases in the process of increasing age. The diagnosis of sarcopenia utilizes total muscle mass and limb muscle mass, and limb muscle mass is expressed as height squared, body weight, and BMI. Each divided value is used as an index, mainly less than 7.23 kg/m2 for men and less than 5.67 kg/m2 for women. Grip strength, standing up from a chair, and walking speed were mainly used as physical function factors, and grip strength less than 27 kg for men and less than 16 kg for women were used as indicators. The limb muscle mass showed a decreasing trend after peaking in the mid-20s in men, and maintaining a gradual peak in women from the mid-20s to the mid-40s, showing a more rapid decline in men. The rate of decrease in muscle mass and strength continues to increase after the age of 20, and muscle strength rapidly decreases after the age of 80. In Korean men, total muscle mass and limb muscle mass show a decreasing trend from the mid-30s, and a more markedly rapid decrease from the age of 60. For women, it remains constant from the age of 30 to the age of 50, then gradually decreases after the mid-50s, and shows a rather rapid decrease after the mid-70s, showing a more gradual decrease than that of men. Men show a sharp decrease from the mid-40s when limb muscle mass is divided by height squared, and women show a marked decrease after 70 years old when limb muscle mass is divided by height squared. Exercise for the prevention and treatment of sarcopenia results in an increase in protein assimilation hormone, an increase in antioxidant activity, a decrease in inflammation, an increase in muscle insulin sensitivity, and an increase in protein synthesis. Resistance exercise is basically used, and aerobic exercise and equilibrium A combination of exercises is effective. In addition, for a more efficient effect of sarcopenia through resistance exercise, it is necessary to supplement nutrition including protein.

Analysis of Characteristics and Internal Resistance of Seawater Secondary Battery according to its Usage Environment (해수이차전지의 사용 환경에 따른 특성 및 내부 저항 분석)

  • Seung-pyo Kang;Jang-mok Kim;Hyun-jun Cho
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.29 no.2
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    • pp.223-229
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    • 2023
  • Seawater batteries are next-generation secondary batteries that use seawater as a cathode. They utilize marine resources to provide competitive prices, high eco-friendliness, and a structure suitable for marine applications. Based on these advantages, pouch types and prismatic types have been studied and developed assuming natural seawater exposure. However, because of the electrical characteristics of the secondary battery, its capacity and internal resistance vary depending on the use environment. These characteristics are not only utilized for predicting the life of a battery but also have a direct effect on the capacity and power suitable for a specific situation. Therefore, the internal resistance was analyzed in this study by measuring the capacity depending on the seawater battery use environment and the state-of-charge-open-circuit-voltage measurement method.

Development of Thermoplastic Carbon Composite Hybrid Bipolar Plate for Vanadium Redox Flow Batteries (VRFB) (바나듐 레독스 흐름전지용 열가소성 탄소 복합재료 하이브리드 분리판 개발)

  • Jun Woo Lim
    • Composites Research
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    • v.36 no.6
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    • pp.422-428
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    • 2023
  • The electrical contact resistance between the bipolar plate (BP) and the carbon felt electrode (CFE), which are in contact by the stack clamping pressure, has a great impact on the stack efficiency because of the relatively low clamping pressure of the vanadium redox flow battery (VRFB) stack. In this study, a polyethylene (PE) composite-CFE hybrid bipolar plate structure is developed through a local heat welding process to reduce such contact resistance and improve cell performance. The PE matrix of the carbon fiber composite BP is locally melted to create a direct contact structure between the carbon fibers of CFE and the carbon fibers of BP, thereby reducing the electrical contact resistance. Area specific resistance (ASR) and gas permeability are measured to evaluate the performance of the PE composite-CFE hybrid bipolar plate. In addition, an acid aging test is performed to measure stack reliability. Finally, a VFRB unit cell charge/discharge test is performed to compare and analyze the performance of the developed PE composite-CFE hybrid BP and the conventional BP.