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Sm을 첨가한 BaTiO<sub>3</sub>계의 재산화 온도 및 시간에 따른 PTC 특성 변화
정용근,최성철,Chung, Yong-Keun,Choi, Sung-Churl 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.3
We investigated the effects of the re-oxidation temperature and time on the positive temperature coefficient (PTC) of resistivity characteristics of Sm-doped $BaTiO_3$ sintered at $1200{\sim}1260^{\circ}C$ for 2 h in a reducing atmosphere (3% $H_2/N_2$), followed by re-oxidization processes in air, in which re-oxidization temperature and time were $600{\sim}1000^{\circ}C$ and $1{\sim}10$h, respectively. The result reveals that Smdoped (Ba,Ca)$TiO_3$ ceramics fired in a reducing atmosphere exhibit low PTC characteristics, whereas the sample re-oxidized at $800^{\circ}C$ for 1 h in air exhibit pronounced PTC characteristics. The room-temperature resistivity and jumping characteristics of resistivity (${\rho}_{max}/{\rho}25^{\circ}C$) decrease with Sm contents. The PTC characteristics with reoxidization time at $800^{\circ}C$ have improved about $2{\sim}3$ orders of magnitude whereas differed according to the sintering temperature. The 0.7 at% Sm-doped (Ba,Ca)$TiO_3$ samples reveal the best PTC characteristics in the present range of formula and processes.
SiC 입자강화 Al-Si 복합재료의 내마멸성에 미치는 Cu , Mg 의 영향
심상한,정용근,박익민 ( Shang Han Shim,Yong Keun Chung,In Min Park ) 한국주조공학회 1990 한국주조공학회지 Vol.10 No.1
N/A The influences of Cu and Mg addition on wear properties of SiC particulate reinforced Al-Si metal(alloy) matrix composites were investigated. Metal matrix composites were prepared by combination of compocasting and hot pressing techniques. The main results obtained are as follows : 1) The composite with Mg addition exhibits letter wear resistance than that with Cu addition. It is considered that Mg addition improved wettability of matal matrix composite by the strong segregation to the SiC / Al matrix interface. 2) After homogenization treatment, it was found that the interfacial segregation of Mg was predominant, while that of Cu was not detected. 3) The SiC / Al-11Si eutectic composite exhibits better wear resistance than the SiC / Al-6Si hypoeutectic composite does. 4) It seems that the increase in the amount of Mg addition affects on the uniform dispersion of SiC particulates, on the refinement of microstructure and on age hardening and these effects cause wear resistance improvement of composites.
압력용기 고온 고압부의 피로손상 예측을 위한 SH 초음파 평가 기법 개발
강용호(Yong Ho Kang),정용근(Yong Keun Chung),박종진(Jong Jin Park),박익민(Ik Min Park) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
Ultrasonic method using SH(shear horizontal) wave has been developed to determine the surface<br/> damage in fatigued material. Fatigue damages based on propagation energy were analyzed by multiregression<br/> analysis and phase measurement in interrupted fatigue test specimen including CrMoV<br/> and 12Cr alloy steel. From the test results, as the fatigue damage increased the propagation time of<br/> the launched waves increased and amplitude of wavelet decreased. Also, analysis for the waveform<br/> modulation showed a reliable estimation, with confidence limit of 97% for 12Cr steel and 95% for<br/> CrMoV steel, respectively. Therefore, It is thought that SH ultrasonic wave technique can be applied<br/> to determine fatigue damage of in-service component nondestructively.
증기터빈의 기동속도 개선을 위한 Probability of Failure 평가법 개발
강용호(Kang Yong Ho),정용근(Chung Yong Keun),박정용(Park Jung Yong),송정일(Song Jung Il) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
During the turbine startup using automatic control system, acceleration rate and loading rate based on stress limits(or allowable stress) of turbine were calculated. In case of thick section of steam turbine, creep and LCF(low cycle fatigue) are principal damages. Therefore stress limits for startup was determined by combined damage evaluation of creep and LCF. In power plant, generally, LDS(linear damage summation) method using creep-fatigue interaction diagram obtained from material test was applied to combined damage evaluation. For conservative evaluation, -2 or -3sigma prediction limits of creep-fatigue interaction diagram was selected and stress limits was calculated by this guideline. However, the excessive margin can be imposed and long-term service life cannot be predicted reasonably because operating history of turbine isn't considered in LDS evaluation. In this paper, to minimize allowable stress margin and the startup time of steam turbine, POF(probability of failure) theory based on test result of low alloy steel and actual operating history of thermal power plant was proposed. Using POF theory, quantitative evaluation of optimum stress limits considered turbine life consumption was performed.
박정용(Jung-Yong Park),정용근(Yong-Keun Chung),박종진(Jong-Jin Park),강용호(Yong-Ho Kang) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
The inner side between HP stationary blades in #1 turbine of Nuclear Power Plant A is damaged by the FAC(flow assisted corrosion) which is exposed to moisture. For many years the inner side is repaired by welding the damaged part, however, FAC continues to deteriorate the original material of the welded blade ring. In this study, we have two stages to verify the integrity of stationary blade ring in nuclear power plant A. In the stage I, replication of blade ring is performed to survey the microstructure of blade ring. In the stage II, the stress analysis of blade ring is performed to verify the structural safety of blade ring. Throughout the two stages analysis of blade ring, the stationary blade ring had remained undamaged.