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임지우 ( Ji Woo Im ),김범준 ( Bum Joon Kim ),김문기 ( Moon K Kim ),임병수 ( Byeong Soo Lim ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.11
The small punch creep (SPC) test has recently received much attention as a new alternative to the conventional uniaxial creep test because it needs only a miniature-sized specimen directly detached from an operating system or component without any serious sampling damages. However, it is difficult to obtain the equivalent uniaxial creep data directly from the SPC data. As a specimen is deformed by a punch in the SPC test, the test result is sensitive to the friction between them. Finite element analyses with various friction coefficients was performed and showed a tendency of increased SPC life with an increased friction coefficient. The necking position predicted by the SPC simulation with a proper friction coefficient showed good agreement with that observed from the real SPC test. Finally, a noble method to convert the SPC load and displacement rate into the equivalent uniaxial creep stress and strain rate, respectively, was established in this study.
초고압균질기 밸브 타입에 따른 coenzyme Q10 나노에멀젼의 제조 및 안정성
임지선(Ji-Sun Lim),강호진(Ho-Jin Gang),윤성우(Sung-Woo Yoon),김형민(Hyeong-Min Kim),석종우(Jong-Woo Suk),김도언(Do-Un Kim),임재각(Jae-Kag Lim) 한국식품과학회 2010 한국식품과학회지 Vol.42 No.5
본 연구에서는 coenzyme Q<SUB>10</SUB>을 나노에멀젼화 하기 위해 초고압균질기를 이용하여 3가지 다른 형태의 밸브를 대상으로 평가를 진행하였으며, 선정된 밸브를 사용하여 제조된 coenzyme QSUB>10</SUB> 나노에멀젼의 품질 특성 및 안정성 평가를 하였다. 초고압균질기를 이용한 coenzyme QSUB>10</SUB> 나노에멀젼 제조 시 최적 조건은 150 MPa, C 밸브, 통과 횟수 3회이었다. 제조된 나노에멀젼은 평균입자 크기가 40 nm, 제타 전위 값이 -57 mV을 나타내어 콜로이드 상태가 충분히 안정하다고 볼 수 있었다. 또한 수용액에 빠르게 분산되었으며, 이때 coenzyme QSUB>10</SUB> 100 mg을 함유한 증류수 100 mL의 투과도 값이 90(%T)로 투명한 용액을 얻을 수 있었다. 제조한 coenzyme QSUB>10</SUB>나노에멀젼은 4℃ 및 25℃에서 12주 동안 보존하여도 침전 또는 부유물을 발생시키지 않았고 coenzyme QSUB>10</SUB> 함량이 변하지 않았으며, 10일간의 동결처리 후에도 안정하였다. pH 2 용액을 제외하고는 pH(4-10) 처리와 열(95℃)처리 및 동결(?20℃)처리 시에도 안정하였다. 따라서 제조된 coenzyme Q<SUB>10</SUB> 나노에멀젼은 액체 형태 등 다양한 식품에 적용할 수 있는 가능성을 확보하였으며, 유통시에는 상온보다는 냉장 보관이 더 적합할 것으로 판단된다. A coenzyme Q10 nanoemulsion was prepared using high pressure homogenization with different valve type conditions (A, B, and C) and cycle numbers (1, 2, and 3). The particle size, transmittance, zeta potential, and coenzyme Q10 content of the prepared coenzyme Q10 nanoemulsion were measured. The stability of the prepared coenzyme Q10 nanoemulsion was evaluated on heating (95℃), freezing (-20℃), and different pH (2-10) conditions. Also, the prepared coenzyme Q10 nanoemulsion was stored at different temperatures of 4, 25, and 40℃ for 12 weeks to evaluate its storage stability. In this study, the optimal conditions of high pressure homogenization for the preparation of a coenzyme Q10 nanoemulsion were identified to be 150 MPa, C valve, and a cycle number of 3. The results showed that the prepared coenzyme Q10 nanoemulsion had an average particle size of 40 nm, generated no deposits or floating matter when stored at either 4 or 25℃ for 12 weeks, and displayed excellent dispersibility and transparency when processed at different pHs (4-10) or heating (95℃) and, freezing (-20℃) conditions. Our results indicated that a coenzyme Q10 nanoemulsion prepared by high pressure homogenization can be used for preparing beverages in the food industry.
High Temperature Fatigue and Creep Behavior of 316L Stainless Steel
임지우,김문진,임병수 기계기술연구소 2000 성균관대학교 논문집 기계기술편 Vol.2 No.1
The heat resistant material may experience static loading, cyclic loading or both during operation. An experimental study of crack growth behavior of STS 216L austenitic stainless steel under fatigue and creep-fatigue loading conditions was carried out on compact tension specimens at various tensile hold times using trapezoidal waveform. In the crack growth experiments under hold time loading conditions, tensile hold times were ranged from 5 seconds to 100 seconds and its behavior was characterized using the ΔK parameter. The fatigue crack growth rates generally increase with hold times. In this material,, however, the crack growth rates decrease when the hold times are relatively short. This is attributed to a dccline in the cyclic crack growth rate as a result of blunting at the crack tip by creep deformation.
STS 316의 크리프 파단 거동에 미치는 장시간 시효의 영향
임지우,임병수 成均館大學校 科學技術硏究所 1999 論文集 Vol.50 No.1
Although type 316 stainless steel is widely used in reactors of petrochemical plants and pipes of steam power plants, the effect of precipitates which form during the long term exposure at service temperature, on creep properties is not known sufficiently. In this study, to investigate the influence of prior aging on the microstructure and creep properties, the 316 stainless steel was first solutionized at 1130℃ for 20 minutes and then the aged specimens for different time of 0hr, 100hrs, 1000hrs and 2200hrs were prepared at 750℃. After heat treatments, the tensile tests both at room temperature and 650℃, the constant load creep rupture tests were carried out. From the experimental results, following conclusions were obtained. (1) The rupture life of 100 hour aged specimens was found to be the shortest. It is resulted from the highest minimum creep rate. And the 0hr aged specimens showed the longest rupture life, followed by 1000hr aged and 2200hr aged specimens. (2) The value of the creep stress exponent, n, decreased as the aging time increased. The n values for the 0hr, 100hr, 1000hr, 2200hr aged specimens were to be measured 13.5, 5.7, 4.4 and 2.9. (3) The creep activation energy varied with the aging time. The activation energies for 0hr, 100hr, 1000hr and 2200hr aged specimens were calculated to be 679.1, 421.6, 527.5 and 517.2 kJ/mol.
열처리를 통한 SNCM220강 권축의 피로특성 향상에 관한 연구
이호성,임지우,임병수 成均館大學校 科學技術硏究所 1997 論文集 Vol.48 No.2
To find out the reason of fracture, specimens were made from the fractured winding shaft and the mechanical properties as well as their microstructures were investigated. Several heat treatments, including caburizing and tempering, were carried out to improve the microstructure, mechanical properties, fatigue crack propagation and rotating bending fatigue characteristics. Through these experiments, following conclusions were obtained, (1) Carburized and tempered specimens showed greatly improved mechanical properties including impact energy, hardness and strength. (2) Crack propagation of the carburized and tempered specimens were faster than that of the original fractured specimens under the same ΔK. However, it was found that, in the early stage, the fatigue crack initiation and growth for the carburized and tempered specimen was more difficult. (3) The fatigue strength of the carburized and tempered specimens increased more than twice than that of the original fractured winding shaft.