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An Auxetic Metamaterial with Tunable Positive to Negative Hygrothermal Expansion by means of Counter-Rotating Crosses
Physica Status Solidi (B) - Basic Solid State Physics ( IF 1.5 ) Pub Date : 2021-05-11 , DOI: 10.1002/pssb.202100137 Teik-Cheng Lim 1
Physica Status Solidi (B) - Basic Solid State Physics ( IF 1.5 ) Pub Date : 2021-05-11 , DOI: 10.1002/pssb.202100137 Teik-Cheng Lim 1
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A type of mechanical metamaterial is proposed, whereby the effective coefficients of thermal and moisture expansions (CTE and CME, respectively) can be tuned from positive to negative values while maintaining a consistently auxetic (negative Poisson's ratio) behavior for the overall structure. Each unit consists of a pair of equal-armed crosses pin jointed at their centers, whereas their ends are connected via bridging beams using pin joints to facilitate free rotation. The bridging beams are of lower modulus and higher hygrothermal expansivity to permit negativity in metamaterial's overall Poisson's ratio and hygrothermal expansion. Two sets of effective Young's modulus, CME and CTE models are developed—one set for large deformation and the other for infinitesimal deformation. Results indicate that the effective Young's modulus is reduced while the expansion coefficients become more negative as the inclination angle of the equal-armed crosses increases, and that the application of tensile and compressive loads increases and decreases the effective Young's modulus, respectively. The establishment of effective zero thermal and moisture expansion conditions facilitates the application of the metamaterial structure that requires auxetic property within highly fluctuating environmental condition.
中文翻译：
通过反向旋转十字可调节正负湿热膨胀的拉胀超材料
提出了一种机械超材料，由此可以将热膨胀和湿膨胀的有效系数（分别为 CTE 和 CME）从正值调整为负值，同时保持整体结构始终如一的拉胀（负泊松比）行为。每个单元由一对等臂十字销组成，它们的中心通过销钉连接，而它们的末端通过使用销钉连接的桥梁连接，以便于自由旋转。桥接梁具有较低的模量和较高的湿热膨胀率，以允许超材料的整体泊松比和湿热膨胀为负值。开发了两组有效杨氏模量、CME 和 CTE 模型——一组用于大变形，另一组用于无穷小变形。结果表明，有效的 Young' 随着等臂交叉的倾角增加，s 模量减小而膨胀系数变得更负，并且拉伸和压缩载荷的施加分别增加和减小有效杨氏模量。有效的零热和湿膨胀条件的建立促进了在高度波动的环境条件下需要拉胀性能的超材料结构的应用。
更新日期：2021-05-11
中文翻译：
通过反向旋转十字可调节正负湿热膨胀的拉胀超材料
提出了一种机械超材料，由此可以将热膨胀和湿膨胀的有效系数（分别为 CTE 和 CME）从正值调整为负值，同时保持整体结构始终如一的拉胀（负泊松比）行为。每个单元由一对等臂十字销组成，它们的中心通过销钉连接，而它们的末端通过使用销钉连接的桥梁连接，以便于自由旋转。桥接梁具有较低的模量和较高的湿热膨胀率，以允许超材料的整体泊松比和湿热膨胀为负值。开发了两组有效杨氏模量、CME 和 CTE 模型——一组用于大变形，另一组用于无穷小变形。结果表明，有效的 Young' 随着等臂交叉的倾角增加，s 模量减小而膨胀系数变得更负，并且拉伸和压缩载荷的施加分别增加和减小有效杨氏模量。有效的零热和湿膨胀条件的建立促进了在高度波动的环境条件下需要拉胀性能的超材料结构的应用。
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