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Off-axis Sputtering 방법으로 제조한 $Bi_2Sr_2Ca_2Cu_3O_x$ 박막의 초전도상 생성에 관한 연구
심창훈,양우석,제정호 한국세라믹학회 1994 한국세라믹학회지 Vol.31 No.7
Off-axis supttering using shielder was used to efficiently prevent negative oxygen ions from resputtering deposited films. In this method, the substrate was located vertically to the target and shielded by the semicircled steel plate. By using this method, the resputtering could be reduced, and 2223 high-Tc phase could be formed at the lower substrate temperature and in the broader temperature region. As increasing the substrate temperature, 2212, 2223, 2212 superconducting phases were formed by turns. 2223 phase was formed above 2$\times$10-2 torr, and 2212 phase was formed above 4$\times$10-2 torr.
심창훈,Do-Young Kim,박재상,유준태,윤영하,이기주 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.5
Postbuckling analyses are conducted to derive the buckling KnockDown Factor (KDF) of pressurized orthogrid-stiffened cylinders for space launch vehicles. The pressurized orthogrid-stiffened cylinders are based on the NASA ETTA1 model. The commercial finite element analysis program, ABAQUS, is used for the numerical analyses. Two different initial imperfection modeling techniques, namely, the Single Perturbation Load Approach (SPLA) and the Single Boundary Perturbation Approach (SBPA), are used to represent the geometric initial imperfection only and geometric and loading imperfections, respectively. The KDFs considering the internal pressure are improved when compared to those with pure axial compression. The KDFs using the SBPA can provide a conservative buckling design that satisfies the lightweight structural design and prevents buckling failure.
심창훈,김도영,전민혁,박재상,김인걸,유준태,윤영하,이기주 한국항공우주학회 2024 International Journal of Aeronautical and Space Sc Vol.25 No.2
Nonlinear postbuckling analyses are conducted to investigate the buckling KnockDown Factors (KDF) for pressurized metallic cylinders. The nonlinear analysis code, ABAQUS, is used to the postbuckling analyses. Various numerical modeling techniques are used to represent the initial imperfections of a cylinder. Measured Geometric Imperfection (MGI) and Single (or Multiple) Perturbation Load Approaches (SPLA or MPLA) are considered to model the geometric initial imperfection modeling techniques, and Single Boundary Perturbation Approach (SBPA) is used to represent the boundary imperfection modeling technique. When the internal pressures of 0 and 40 kPa, the SPLA can provide less conservative KDFs. However, the robust KDFs for the cylinder subjected to an internal pressure of 100 kPa are derived using the SBPA. These results show that the initial imperfection modeling must be appropriately selected considering the internal pressure levels of the thin-walled cylinder.
반구형 및 타원형 샌드위치 공통 격벽 구조에 대한 좌굴 설계 기준 도출 및 비교
심창훈,김기섭,이창민,박재상,이준성 한국항공우주학회 2024 韓國航空宇宙學會誌 Vol.52 No.6
외부 압력을 받는 반구형 및 타원형 샌드위치 공통 격벽 구조에 대하여 ABAQUS를 이용한 비선형 후좌굴 해석을 수행하고, 좌굴 설계 기준인 좌굴 Knockdown factor (KDF)를 도출하였다. 초기 결함의 유무에 상관없이 반구형 샌드위치 공통 격벽 구조의 전역 좌굴 하중이 타원형 구조에 비해 최소 73.12% 높게 계산되었다. 따라서 좌굴 하중의 관점에서는 반구형 샌드위치 공통 격벽 구조가 경량 설계에 유리함을 확인하였다. 그러나 KDF는 타원형 샌드위치 공통 격벽 구조가 반구형 구조에 비해 13.43% 높게 도출되어 KDF 측면에서는 타원형 공통 격벽 구조가 반구형 구조에 비하여 효율적인 구조 경량화를 제공함을 확인하였다. 본 연구에서 도출된 샌드위치 공통 격벽 구조에 대한 KDF는 기존 NASA의 좌굴 설계 기준보다 최소 181.45% 높게 도출되어 폼 코어 쉘 구조를 사용하는 샌드위치 공통 격벽 구조의 좌굴 설계 기준이 적절히 개선됨을 확인하였다. Nonlinear postbuckling analyses of hemispherical and elliptical sandwich common bulkheads under external pressure are performed using ABAQUS to derive buckling knockdown factors (KDF). For the both cases with and without the initial imperfection, the global buckling loads of the hemispherical common bulkheads are at least 73.12% higher than those of the elliptical common bulkheads. Therefore, the hemispherical sandwich common bulkhead is more favorable for the lightweight design than the elliptical shell from the global buckling load point of view. However, the KDF of the elliptical sandwich common bulkhead is 13.43% higher than that of the hemispherical shell. Therefore, in terms of the KDF, the elliptical sandwich common bulkhead provides an efficient structural weight reduction compared to the hemispherical shell. The derived KDFs are at least 181.45% higher than the previous buckling design criteria; thus, it is shown that the buckling design criteria for sandwich common bulkheads using a foam core sandwich shell are appropriately improved.