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장건익,안병국,김동건 대한용접접합학회 2002 대한용접·접합학회지 Vol.20 No.2
The fatigue life is predicted on tensile-shear spot weldment made from Al-Mg alloy sheet with thickness of 0.8mm using Mitchell's method and uniform material law by $B{\ddot{a}}umel$ and Seeger based on local strain approach. The fatigue properties of critical HAZ region are estimated from the tensile property using simple hardness method. To predict the fatigue life of spot weldment, the local stresses and strains at the potential critical region are estimated by Neuber's rule. The predicted fatigue life based on uniform material law using HAZ's material properties provides good results within a factor of 3, conservatively.
Dielectric Properties of Bi3.25Nd0.75Ti3O12 Thin Film
장건익,김기범,윤대호 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
Bi4xNdxTi3O12 (BNdT)thin lms with the composition (x = 0.75) have been prepared on Pt/Ti/SiO2/Si(100) substrates by using metal-organic precursor solutions by a chemical deposition method. The lms were annealed at various temperatures from 550 C to 650 C. Above 600 C, well-crystallized BNdT thin lms with bismuth layered perovskite structure were obtained and revealed a random orientation without typical (00l) preferred diraction patterns. The BNdT lm annealed at 650 C exhibited a remanent polarization (2Pr) of 56 C/cm2 and coercive eld (2Ec) of 232 kV/cm, respectively. The capacitor did not show any signicant fatigue up to 8 1010 read/write switching cycles at a frequency of 1 MHz, regardless of annealing temperature.
플래셔 패턴을 활용한 종이접기 기반의 전개형 반사판 구조물
장건익,김태현,이대영,한재흥 한국항공우주학회 2023 韓國航空宇宙學會誌 Vol.51 No.7
The development of small satellite payloads in current times requires efficient use of limited space, while achieving high performance. For high-performance missions, reflector antennas with a certain size or larger may be necessary, but spatial constraints can pose a challenge. To overcome these limitations, researchers are designing these structures in deployable configurations. In this research, we propose the origami-based deployable structure, which can be easily and efficiently packed. The structure is able to deploy itself by applying a compliant flexure hinge. In order to evaluate the performance of the proposed deployable reflector structure, the packaging efficiency, surface error, and focus error are analyzed in relation to changing the design parameter. A deployable prototype is constructed using a torsion-based compliant hinge. Finally, the position change of specific points is experimentally measured to analyze a deployment repeatability. 현재 개발 중인 소형 및 초소형 위성의 탑재체들은 높은 성능을 가지기 위해 위성체의 한정적인 공간을 효율적으로 사용하여 배치해야한다. 특히 면적이 성능에 직결되는 반사판 구조의 경우 고성능의 임무를 수행하기 위해선 필연적으로 특정 크기 이상이 되어야 하는데, 소형화되는 위성체의 공간적 제약 문제를 해결하고자 전개형 구조 개념을 적용한 연구가 다수 수행 중이다. 본 논문에서는 간단한 전개 방식과 높은 수납 효율로 주목받고 있는 종이접기 구조에 기반하여, 재료의 탄성을 이용한 유연 힌지(Compliant Flexure Hinge)가 적용된 ‘종이접기 기반의 전개형 반사판 구조물’을 제안한다. 제안한 구조물이 전개형 구조물로써, 전개형 반사판으로써의 성능을 파악하기 위하여 매개변수의 변화에 따른 수납 효율, 표면 오차, 초점 오차에 대해서 분석한다. 제안된 종이접기 반사판 구조물을 전개가 가능한 구조물로 제작하기 위해 비틀림 기반의 유연 힌지(Torsion-based Compliant Hinge)를 이용하여 프로토타입을 제작하고, 구조의 전개 반복성을 확인하기 위하여 제작된 구조의 특정 점들의 위치 변화를 실험적으로 측정하여 분석한다.
액체질소 냉각 시 임의의 홀을 가진 초전도체의 열응력 해석
장건익,이호진,김찬중,한영희,성태현,Jang, G.E.,Lee, H.J.,Kim, C.J.,Han, Y.H.,Sung, T.H. 한국초전도학회 2009 Progress in superconductivity Vol.11 No.1
Temperature distributions and thermal stresses were calculated and analyzed to investigate the effect of the artificial holes to the transient behaviors of the superconductors which was cooled in liquid nitrogen. Three dimensional finite element method was used to calculated the transient temperature and thermal stresses in the superconductors. The cooling speed of the superconductors with holes is faster than those without holes. Because the thermal stresses calculated in the superconductors can be relaxed by the distributed holes, the volume of the peak tensile stress decreases during the cooling in liquid nitrogen. If optimal metal, which can maintain the relaxation of thermal stresses, is used to fill and reinforce the artificial holes, the probability of failure of the superconductors may be decreased by the decrease of volume of peak tensile stress.