발전기 고정자 냉 각 계통에서 부식에 의한 미세 입자생성과 침적에 관한 연구

Thesis (master`s)--서울대학교 대학원 :원자핵공학과,1996.Maste

연속 핵생성되는 기공의 확산성장으로 인한 크립파괴 및 크립균열전파

학위논문(박사) - 한국과학기술원 : 기계공학과, 1988.2, [ viii, 111 p. ]Creep rupture and creep crack growth by grain boundary cavitation have been concerns of practical interest for several decades. Existing models for the diffusive growth of cavities on grain boundaries are usually based on the assumptions of periodic cavity spacing and simultaneous cavity nucleation. However, creep cavities nucleate continually during the creep process at random grain boundary sites, and it is appropriate to investigate non-periodic, and stochastic models for diffusive creep rupture. The present study shows an analysis of diffusional cavity growth when cavities are continually nucleating at random grain boundary sites. For the creep rupture analysis, the method treats a 2-D version of the real 3-D problem. Based on the analysis by Yu and Chung[1,2] when cavities of varying size are randomly distributed on the bicrystal interface, rupture times are numerically calculated by using the 2-D cavity nucleation rates which are deduced from 3-D cavity nucleation data in such a way that the average inter-cavity spacings of the two cases are always equal. Predicted rupture times show agreements with experimental data within a factor of 3 for all the materials studied under various stress and temperatureranges, and manifest stronger stress dependence than expected from the models which do not take cavity nucleation into account. The most revealing facts from the analysis are that cavity nucleation is the most important factor determining the rupture time and that differences in cavit growth mode really do not matter. When a macroscopic crack is embedded in polycrystalline solids, the extension of the crack at creeping temperature is usually described by specific load parameters such as $C^*$ or K, which depends on the stress field around the crack tip. Under these stresses, grain boundary cavities develope ahead of the crack tip, and the crack extends when the damage ahead of the crack tip reaches a critical value. In the present study of crack extension, ...한국과학기술원 : 기계공학과

Surface Model of the Gastrointestinal Tract Constructed From the Visible Korean

Most currently available three-dimensional surface models of human anatomic structures have been artistically created to reflect the anatomy being portrayed. We have recently undertaken, as part of our Visible Korean studies, to build objective surface models based on cross-sectional images of actual human anatomy. Objective of the present study was to elaborate surface models of the GI tract and neighboring structures that are helpful to medical simulation. The GI tract from stomach to anal canal was outlined and reconstructed from sectioned images of the Visible Korean. The outlining procedure was supported by computational filtering and interpolation using commercially available software. The GI tract was divided into several parts, and each of these parts was surface reconstructed and then united with neighboring parts to produce a surface model of the complete GI tract

A Rational Design of Coin-type Lithium-metal Full Cell for Academic Research

코인형 전지는 리튬 이차 전지 연구의 주요 평가 플랫폼으로써 새로운 소재 및 개념을 발굴하고 차세대 전지의 기초 연구에도 큰 기여를 하고 있다. 리튬 금속 전지는 500 Wh kg−1 이상의 에너지 밀도를 구현할 수 있어 유망한 차세대 리튬 이차 전지 후보군으로 고려되고 있으나 , 덴 드라이트 형태의 리튬 전착과 함께 극심한 부피 변화 및 표면적 증가라는 성능 열화에 매우 취 약하다 . 특히 , 리튬 금속 전지의 수명은 전해질 양, 리튬 두께 , 내부 압력 등과 같은 전지 설계 및 구조에 매우 의존하기 때문에 코인셀 수준에서의 성능 평가 및 신뢰성에 치명적이다 . 따라서 , 기존 코인셀 구조를 개선한 리튬 금속 음극 특화 전지 설계 및 규격화가 요구된다 . 본 연구에 서는 상용수준에서의 주요 전지 설계 인자인 극소량의 전해질과 높은 양극 로딩 레벨 , 박막 리 튬 사용 등의 환경에서 성능 및 재현성을 확보한 코인셀 구조를 제안한다 . 양극과 음극의 면적 비를 1에 근접하게 제어하여 비활성 공간을 최소화하고 용량 저하현상을 완화시켰다 . 또한 , 코인 셀 내 압력을 정량화하여 압력의 균일성이 중요한 인자임을 규명하고 유연성 고분자 (PDMS) 필름 도입과 내부 부품의 변화를 통해 기존보다 높고 (0.6 MPa → 2.13 MPa) 균일한 압력 (표준편차 : 0.43 → 0.16)이 가하도록 개조하였다 . 이를 통해 최적의 설계를 정립을 통해 기존보 다 향상된 재현성을 확인하였다. Coin cell is a basic testing platform for battery research, discovering new materials and concepts, and contributing to fundamental research on next-generation batteries. Li metal batteries (LMBs) are promising since a high energy density (~500 Wh kg-1) is deliverable far beyond Li-ion. However, Li dendrite-triggered volume fluctuation and high surface cause severe deterioration of performance. Given that such drawbacks are strongly dependent on the cell parameters and structure, such as the amount of electrolyte, Li thickness, and internal pressure, reliable Li metal coin cell testing is challenging. For the LMB-specialized coin cell testing plat-form, this study suggests the optimal coin cell structure that secures performance and repro- ducibility of LMBs under stringent conditions, such as lean electrolyte, high mass loading of NMC cathode, and thinner Li use. By controlling the cathode/anode (C/A) area ratio closer to 1.0, the inactive space was minimized, mitigating the cell degradation. The quantification and imaging of inner cell pressure elucidated that the uniformity of the pressure is a crucial matter to improving performance reliability. The LMB coin cells exhibit better cycling retention and reproducibility under higher (0.6 MPa → 2.13 MPa) and uniform (standard deviation: 0.43 → 0.16) stack pressure through the changes in internal parts and introducing a flexible polymer (PDMS) film.FALS