• Steel and Composite Structures
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• 제49권4호
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• pp.393-405
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• 2023

In this paper, the energy absorption capability of a novel cruciform composite lattice structure was evaluated through the simulation of compression tests. For this purpose, several test samples of Polylactic acid cellular reinforced with continuous glass fibers were prepared for compression testing using the additive manufacturing method of material extrusion. Using a conventional path design for material extrusion, multiple debonding is probable to be occurred at the joint regions of adjacent cells. Therefore, an innovative printing path design was proposed for the cruciform lattice structure. Afterwards, quasistatic compression tests were performed to evaluate the energy absorption behaviour of this structure. A finite element model based on local material property degradation was then developed to verify the experimental test and extend the virtual test method. Accordingly, different combinations of unit cells' dimensions using the design of the experiment were numerically proposed to obtain the optimal configuration in terms of the total absorbed energy. Having brilliant energy absorption properties, the studied cruciform lattice with its optimized unit cell dimensions can be used as an energy absorber in crashworthiness applications. Finally, a cellular structure will be suitable with optimal behavior in crush load efficiency and high energy absorption.

• 대한전자공학회논문지
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• 제25권2호
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• pp.119-124
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• 1988

Real-time adaptive lattice predictor was implemented on the TMS32020 DSP chip for digital signal processing. The implemented system was composed of Input-Output units and centrla processing-control unit and its supporting assembly soft ware. The performance of hardware realization was verified by comparing input signal and one-step prediction signal which are calcualted by the real-time adaptive lattice predictor. As a result, for 4 stage lattice structure, the maximum running frequency was obtained as 6.41 KHz in this experiment.

• Advances in aircraft and spacecraft science
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• 제9권5호
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• pp.377-400
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• 2022

The aim of this work is a numerical comparison (FEM) between lattice pyramidal-core panel and honeycomb core panel for different core thicknesses. By evaluating the mid-span deflection, the shear rigidity and the shear modulus for both core types and different core thicknesses, it is possible to define which core type has got the best mechanical behaviour for each thickness and the evolution of that behaviour as far as the thickness increases. Since a specific base geometry has been used for the lattice pyramidal core, the comparison gives us the opportunity to investigate the unit cell strut angle giving the higher mechanical properties. The presented work considers a detailed FEM modelling of a standard 3-point bending test (ASTM C393/C393M Standard Practice). Detailed FEM modelling addresses to detailed discretization of cores by means of beam elements for lattice core and shell elements for honeycomb core. Facings, instead, have been modelled by using shell elements for both sandwich panels. On lattice core structure, elements of core and facings are directly connected, to better simulate the additive manufacturing process. Otherwise, an MPC-based constraint between facings and core has been used for honeycomb core structure. Both sandwich panels are entirely built of Aluminium alloy. Prior to compare the two models, the FEM sandwich panel model with lattice pyramidal core needs to be validated with 3-point bending test experimental results, in order to ensure a good reliability of the FEM approach and of the comparison. Furthermore, the analytical validation has been performed according to Allen's theory. The FEM analysis is linear static with an increasing midspan load ranging from 50N up to 500N.

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제5권2호
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• pp.95-100
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• 1998

In this note we consider some basic facts concerning abstract M spaces and investigate extremal structure of the unit ball of bounded linear functionals on $\sigma$-complete abstract M spaces.

• Bulletin of the Korean Chemical Society
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• 제32권2호
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• pp.451-454
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• 2011

The traditional BCS superconductors $AOs_2O_6$ (A=K, Rb, and Cs) were investigated to find the relationship between their structures and superconducting transition temperatures. The $T_c$ decreases with increasing the unit cell parameter of $AOs_2O_6$. This is in contrast to the case of conventional BCS superconductivity in a single bond model, where $T_c$ may increase with increasing the the unit cell parameter since the DOS at Fermi level increases as the unit cell parameter increases. Instead, the $T_c$ of a $\beta$-pyrochlore oxide is proportional to the lattice softness of the compound.

• 한국산학기술학회논문지
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• 제22권6호
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• pp.19-26
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• 2021

격자 구조체는 강도 및 강성, 초경량 및 에너지 흡수 능력 등의 우수성을 가지고 있어서 전방위 산업에서 주목을 받고 있으나, 다양한 장점에도 불구하고 복잡한 형상에 따른 제조 공정의 어려움으로, 현재까지 광범위한 상용화 및 사용은 제한되고 있다. 한편 적층 제조는 전통적인 제조 방법으로는 불가능한 복잡한 기하학적 형상 제조가 가능한 기술로써, 격자 구조체 제조를 위한 최적 기술로 주목을 받고 있다. 본 연구에서는 3차원 좌표 방법으로 단위 셀을 형성하고, 단위셀의 바운더리 박스 크기 및 스트럿 반경에 따른 상대 밀도의 관계식을 도출하였다. 본 연구에서는 Simple Cubic(SC), Body-Centered Cubic(BCC) 및 Face-Centered Cubic(FCC)을 모델링 소프트웨어를 사용하여 상대 밀도 맞춤형 구조체를 설계하였다. 본 연구에서 제안한 상대 밀도 산출식 정확도는 SC, BCC 및 FCC에서 98.3 %, 98.6 % 및 96.2%의 신뢰성을 확보하였다. 격자 구조체를 대상으로 시뮬레이션 수행 결과, 동일한 셀 배열 조건에서는 상대 밀도가 커짐에 따라 항복 하중이 커지고, 동일 배열 조건에서는 SC, BCC, FCC 순으로 압축 항복 하중이 작아지는 결과가 나타났다. 최종적으로 20 mm × 20 mm × 20 mm 크기의 구조체는 SC 단위 셀을 3×3×3 배열로 구성하는 것이 압축 하중에 대한 구조적 최적화가 가능한 것으로 나타났다.

• 콘크리트학회논문집
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• 제20권6호
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• pp.705-712
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• 2008

본 연구에서는 그라운드 구조법을 이용하여 콘크리트 구조형태의 최적화에 대한 수치 실험을 하였다. 마이크로 격자 모델은 단위 셀의 집합체로 구성되었다. 해석 과정은 각 부재의 응답계를 강성에 피드백 시켜서 유한요소해석을 반복하였다. 이 해석의 반복을 통하여, 트러스 모델은 수리적 최적화 수법이 아니라 국소적인 응력 상태를 이용하여 위상적인 구조 형태와 구조적 형상을 표현하였다. 격자 트러스 모델을 여러 예제에 적용하여 형상 배치 문제를 해석하는데 성공하였다.

• Applied Microscopy
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• 제44권4호
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• pp.144-149
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• 2014

A strategy for phase identification of precipitates in high Al-containing austenitic and ferritic steels using electron diffraction (ED) is studied. Comparative studies of the various Al-containing precipitates (k-carbide, $Ni_3Al$, $Fe_3Al$, FeAl) show the similarities of crystal structure and lattice parameter. However, the slight differences of lattice parameter and structure display characteristic ED patterns (EDPs) which can be identified. $L1_2$ k-carbide and $Ni_3Al$ can be differentiated by the length of ${\rightarrow}_g$ (the reciprocal lattice vector), even though they show perfectly identical shapes of EDPs. $DO_3$ $Fe_3Al$ and $B_2$ FeAl show the characteristic EDs in [110] and [112] beam directions due to the differences of Fe site occupancies in unit cells. k-carbide, $Ni_3Al$, and FeAl show also the similar EDs in [112], [112], and [110] beam directions, respectively. All the possible similarities of EDs among each phases and the strategy for phase identification are discussed on the bases of kinematical ED simulation.

• Composites Research
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• 제33권3호
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• pp.169-175
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• 2020

콘형 복합재 격자 구조체의 강성 평가를 위한 두 종류의 시편 단위 압축 및 인장 시험을 수행하였으며 유한요소해석 결과와 비교하였다. 구조체는 높이별로 반경이 변화하는 콘형이므로 단순 압축 및 인장 시험이 어려우므로 시험 수행이 가능한 형태의 시편 및 지그를 제작하여 시험을 수행하였다. 압축 시험이 가능하도록 단위 격자 구조체를 Subelement 형태로 가공하였으며, 압축 시험을 수행하여 측정된 섬유방향 압축 변형률을 유한요소해석 결과와 비교하여 헬리컬 리브의 강성을 확인하였다. 후프 리브의 강성 평가를 위해서는 구조체에서 후프 링 시편을 가공하여 인장 시험을 수행하였다. 후프 링에 인장 하중을 가하여 굽힘 변형이 크게 발생하도록 하였으며, 두께 방향 섬유체적비를 고려한 유한요소해석 결과와 비교하여 후프 리브의 강성을 확인하였다.

• Bulletin of the Korean Chemical Society
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• 제31권8호
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• pp.2247-2254
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• 2010

The surface structures of copper phthalocyanine (CuPc) thin films deposited on sulphur-passivated and plane perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)-covered InAs(100) surfaces have been studied by low energy electron diffraction (LEED) and van der Waals (vdW) intermolecular interaction energy calculations. The annealing to $300^{\circ}C$ and $450^{\circ}C$ of $(NH_4)_2S_x$-treated InAs(100) substrates produces a ($1{\times}1$) and ($2{\times}1$) S-passivated surface respectively. The CuPc deposition onto the PTCDA-covered InAs(100) surface leads to a ring-like diffraction pattern, indicating that the 2D ordered overlayer exists and the structure is dominantly determined by the intermolecular interactions rather than substrate-molecule interactions. However, no ordered LEED patterns were observed for the CuPc on S-passivated InAs(100) surface. The intermolecular interaction energy calculations have been carried out to rationalise this structural difference. In the case of CuPc unit cells on PTCDA layer, the planar layered CuPc structure is more stable than the $\alpha$-herringbone structure, consistent with the experimental LEED results. For CuPc unit cells on a S-($1{\times}1$) layer, however, the $\alpha$-herringbone structure is more stable than the planar layered structure, consistent with the absence of diffraction pattern. The results show that the lattice structure during the initial stages of thin film growth is influenced strongly by the intermolecular interactions at the interface.