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Optimal design of “Shellular”, a micro-architectured material with ultralow density
Nguyen, Ban Dang,Cho, Jeong Shik,Kang, Kiju Elsevier 2016 Materials & Design Vol.95 No.-
<P><B>Abstract</B></P> <P>Recently, a new ultralow-density material with micro-architecture, “Shellular” was introduced. Shellular consists of continuous smooth shells and has a typical hierarchical architecture across multiple scales. In this work, an optimal design for Shellular is sought in a simplified as well as realistic configuration for the maximum possible strength or modulus for a given density. After a series of analyses and design processes such as the selection of key geometrical parameters, the derivation of empirical equations, failure analysis, and corresponding optimization, optimized models were produced that are expected to have strengths about 2.5 times and Young's moduli about 4 times as high as those of the prior non-optimized Shellular specimens. Specifically, the optimized model of thin Ni shells with relative density of 0.002 and inclination angle of 60° could gain the strength of 0.1MPa and the Young's modulus of 5.06MPa. However, to achieve the highest mechanical properties among the competitors in ultralow density domain, a more radical approach needs to be applied to the geometrical optimization of Shellular.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Shellular is a new hierarchical ultralow-density material with micro-architecture of shells. </LI> <LI> An optimal design for Shellular is sought for the maximum possible strength or modulus. </LI> <LI> For that purpose, modeling algorithm, empirical equations & design maps are developed. </LI> <LI> The optimized models give much higher strength & modulus, but still not the world best. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Design of the <i>P-</i>surfaced shellular, an ultra-low density material with micro-architecture
Nguyen, Ban Dang,Han, Seung Chul,Jung, Yoon Chang,Kang, Kiju Elsevier 2017 Computational materials science Vol.139 No.-
<P><B>Abstract</B></P> <P>The <I>P</I>-surface is an intersection-free smooth surface that has constant mean curvature everywhere on the surface, and periodicity in three directions in 3D space. A cellular material composed of thin shells in this configuration, named Shellular, reveals <I>stretching-dominated</I> deformation under external loading. The thin continuous shell of a Shellular could play the role of a transfer interface between the two sub-volumes, as well as a mechanical load support. This paper presents a preliminary study to design an optimal shape of the <I>P</I>-surfaced Shellular. Analysis of the geometry and finite element analyses are performed to investigate the effects of the geometric parameters and boundary conditions on their mechanical properties. It is shown that the geometry and mechanical properties of a <I>P</I>-surfaced Shellular can be expressed in empirical equations with only two independent dimensionless parameters, i.e., the volume fraction and the ratio of the wall thickness to cell size; and that the effect of the volume fraction is substantial. A low volume fraction is very beneficial to achieve high strength, and suppresses elastic buckling to delay the transition of the failure mode from plastic yielding to elastic buckling as the wall thickness is decreased.</P> <P><B>Highlights</B></P> <P> <UL> <LI> <I>P</I>-surface is a smooth surface with constant mean curvature and triple periodicity. </LI> <LI> A <I>P</I>-surfaced shell structure, Shellular, reveals <I>stretching-dominated</I> deformation. </LI> <LI> Its mechanical properties are given by volume fraction and relative wall thickness. </LI> <LI> Low volume fraction delays elastic buckling of the shell, resulting in high strength. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
음의 푸아송비를 갖도록 변환된 와이어 직조 Kagome
강대승(Dae Seung Kang),한승철(Seung Chul Han),박종우(Jong Woo Park),Nguyen Dang Ban,강기주(Kiju Kang) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.9
와이어 직조 Kagome는 와이어로 직조된 Periodic Cellular Metal의 일종으로서 Kagome 구조로 이루어져 있다. 와이어 직조 Kagome는 무게 대비 높은 강도와 강성을 가지면서 대량 생산에도 큰 가능성을 가지는 것으로 알려졌다. 본 연구에서는 α-cristobalite 구조적 특성을 모사하여 음의 푸아송비를 갖는 새로운 직조 구조체를 개발하였다. 와이어 직조 Kagome를 제작한 후 사면체 단위셀 부분을 강구와 Epoxy를 이용하여 채우고, 초기 변형을 주어 시편을 제작하였다. 또한 FEA 시뮬레이션을 통해 제작 가능성을 확인하고, 실제 제작한 구조체를 대상으로 기계적 특성을 연구하였다. Wire-woven Kagome is a kind of Periodic Cellular Metal, which is known to have high strength, stiffness for its weight, and potential for mass production. In this work, we developed a new structure that mimics α-cristobalite. First, an ordinary wire-woven Kagome was fabricated using metallic wires, and the tetrahedral cells were then filled with metal balls and epoxy. The wire-woven Kagome was transformed to have a negative Poisson’s ratio by carrying out a specified amount of initial deformation. The fabrication possibility and kinematic behavior were checked by using FEA simulation. Finally, the mechanical properties were measured using compressive tests.