In-plane tensile elasticity of a novel anti-tetrachiral cellular structure
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摘要: 提出了由半周期正弦梁组成的新型反四手性蜂窝结构。基于能量法对蜂窝结构面内拉伸弹性进行了理论分析,通过有限元仿真和实验测试对理论模型进行了验证,并讨论了几何参数对结构拉伸性能的影响,最后将本文结构与传统手性结构进行性能比较,探讨了本文结构的变形机制。结果表明:该新型结构具有优秀的变形能力,其等效弹性模量可比原材料低5~6数量级,且具有低至−8.7的大等效负泊松比范围,接近传统手性结构等效泊松比范围的2倍。作为一种独特的新型拉胀结构,其高度可调的弹性模量和泊松比可用于开发缓冲装置、医用支架、变体机翼等,在船舶、医疗、航空航天等领域具有巨大的应用潜力。Abstract: A novel anti-tetrachiral cellular structure composed of half-periodic sine beams was proposed. The in-plane tensile elasticity of the cellular structure was theoretically analyzed based on the energy method, then the theoretical model was verified by finite element simulation and experimental test, and the influence of geometric parameters on the tensile properties of the structure was discussed. Finally, the properties of the proposed structure were compared with those of the conventional chiral structure, and deformation mechanism of the proposed structure was also discussed. The results show that the novel structure has excellent deformation capability. The in-plane equivalent elastic modulus can be 5-6 orders of magnitude lower than the raw material. The structure also has a range of large equivalent negative Poisson’s ratio with the lower bound of −8.7, which is nearly 2 times larger than that of conventional chiral structure. As a unique novel auxetic structure, its highly tunable elastic modulus and Poisson’s ratio can be used to develop buffer devices, medical stents, morphing wings, etc., which has great application potential in the field of shipbuilding, medical treatment, aerospace and so on.
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图 2 半周期正弦梁蜂窝单元结构参数
L—Spanwise length of the half-period sine beam along the horizontal direction; VL—Chordwise height of the half-period sine beam along the horizontal direction; H—Spanwise length of the half-period sine beam along the vertical direction; VH—Chordwise height of the half-period sine beam along the vertical direction; t—Thickness of the beams; b—Gauge thickness
Figure 2. Structural parameters of unit cell with half-periodic sine beams
图 3 反四手性蜂窝结构沿x方向单轴拉伸
Figure 3. Uniaxial stretching along the x-direction of the anti-tetrachiral cellular structure
${\sigma _x}$—Equivalent stress along the x-direction; Δ1, Δ2, Δ3 and Δ4—Virtual dividing lines; ${P_x}$ and ${P_y}$—Tensile loads along the x- and y-directions, respectively; ${S_x}$ and ${S_y}$—Shear loads along the x- and the y-directions, respectively; ${M_1}$ and ${M_2}$—Interacting bending moments of the cross sections
图 13 正弦半周期型反四手性蜂窝结构与传统手性结构在不同壁厚下随相对密度
${\rho _{\text{r}}}$ 变化的性能比较(传统手性结构:$r = 5\;{\text{mm}}$ ,${L_x} = {L_y} = 20\;{\text{mm}}$ ;正弦半周期型结构:$H = L = 20\;{\text{mm}}$ )Figure 13. Comparison of the properties between the half-periodic sine anti-tetrachiral cellular structure and conventional chiral structures under different thickness varying with relative density
${\rho _{\text{r}}}$ (Conventional chiral structure:$r = 5\;{\text{mm}}$ ,$ {L_x} = {L_y} = 20\;{\text{mm}} $ ; Half-periodic sine anti-tetrachiral structure:$H = L = 20\;{\text{mm}}$ )表 1 几何参数及无量纲参数设定
Table 1. Geometric parameters and dimensionless parameters setting
Geometric parameter Dimensionless parameter L Aspect ratio $\alpha = L/H$ VL Thickness ratio $ \beta = t/H $ H Gauge thickness ratio $\gamma = b/H$ VH Chord ratio of the horizontal beam $ \xi = {V_{\text{L}}}/H $ t Chord ratio of the vertical beam $\varphi = {V_{\text{H}}}/H$ b — 表 2 有限元仿真周期条件和边界条件
Table 2. Periodic conditions and boundary conditions for finite element simulation
Condition Uniaxial loading along the x-direction Periodic
condition${u_x}\left( {\text{E}} \right) = {u_x}\left( {\text{F}} \right)$ ${u_x}\left( {\text{E}} \right) = {u_x}\left( {\text{F}} \right)$
${\theta _z}\left( {\text{A}} \right) = {\theta _z}\left( {\text{B}} \right)$ ${\theta _z}\left( {\text{C}} \right) = {\theta _z}\left( {\text{D}} \right)$
${\theta _z}\left( {\text{E}} \right) = {\theta _z}\left( {\text{F}} \right)$ ${\theta _z}\left( {\text{G}} \right) = {\theta _z}\left( {\text{H}} \right)$Boundary condition ${u_x}\left( {\text{A}} \right) = 0$
${u_x}\left( {\text{C}} \right) = 0$ ${u_y}\left( {\text{C}} \right) = 0$
${u_x}\left( {\text{B} } \right) = {\varepsilon _x} 4 L$
${u_x}\left( {\text{D} } \right) = {\varepsilon _x} 4 L$Notes: ${u_x}$—Displacement along the x-direction; ${u_y}$—Displacement along the y-direction; ${\theta _z}$—Rotation angle around the z-axis; ${\varepsilon _x}$—Strain along the x-direction. 表 3 实验与理论值的比较
Table 3. Comparison between the experimental and theoretical results
Number Parameter of the unit
($H = L = 20\;{\text{mm}}$)$ {E_x}/E $
(Theoretical value)${E_x}/E$
(Experiment value)Error/% ① $\begin{gathered} \xi = \varphi = 0.5 \\ t = 1\;{\text{mm}} \\ \end{gathered} $ $4.13 \times {10^{ - 5}}$ $3.74 \times {10^{ - 5}}$ $9.4$ ② $\begin{gathered} \xi = \varphi = 0.5 \\ t = 2\;{\text{mm}} \\ \end{gathered} $ $3.29 \times {10^{ - 4}}$ $2.99 \times {10^{ - 4}}$ $9.1$ ③ $\begin{gathered} \xi = \varphi = 0.5 \\ t = 3\;{\text{mm}} \\ \end{gathered} $ $1.10 \times {10^{ - 3}}$ $9.98 \times {10^{ - 4}}$ $9.3$ ④ $\begin{gathered} \xi = 0.3,\varphi = 0.5 \\ t = 2\;{\text{mm}} \\ \end{gathered} $ $1.01 \times {10^{ - 4}}$ $9.21 \times {10^{ - 4}}$ $8.8$ ⑤ $\begin{gathered} \xi = 0.8,\varphi = 0.5 \\ t = 2\;{\text{mm}} \\ \end{gathered} $ $1.08 \times {10^{ - 4}}$ $1.00 \times {10^{ - 4}}$ $7.4$ ⑥ $\begin{gathered} \xi = 0.5,\varphi = 0.3 \\ t = 2\;{\text{mm}} \\ \end{gathered} $ $3.37 \times {10^{ - 4}}$ $3.07 \times {10^{ - 4}}$ $8.9$ ⑦ $\begin{gathered} \xi = 0.5,\varphi = 0.8 \\ t = 2\;{\text{mm}} \\ \end{gathered} $ $3.18 \times {10^{ - 4}}$ $2.92 \times {10^{ - 4}}$ $8.2$ 表 4 传统手性蜂窝几何参数
Table 4. Geometric parameters of conventional chiral structures
Geometric parameter Dimensionless parameter Radius of central rigid node $r$ Transverse beam ratio ${\alpha _x} = {L_x}/r$ Length of transverse tangential ligaments ${L_x}$ Longitudinal beam ratio ${\alpha _y} = {L_y}/r$ Length of longitudinal tangential ligaments ${L_y}$ Thickness ratio $\beta = t/r$ Thickness of the beams $t$ Gauge thickness ratio $\gamma = b/r$ Gauge thickness $b$ — -
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