超材料中的反向和可编程坡印廷效应
Inverted and programmable Poynting effects in metamaterials
摘要：
坡印亭效应一般表现为材料在垂直于所施加的剪切变形（扭转）的方向上的延伸，并且是难以设计的材料参数。与各向同性固体不同，在设计的结构中，剪切变形和法向变形之间的特殊耦合可以实现并用于实际应用。在这里，我们设计了一种超材料，它可以被编程为在扭转下收缩或伸展，并在压缩下经历非线性扭曲。首先，我们表明，我们的系统具有一种新型的倒坡印廷效应，轴向压缩引起的非线性扭转。然后，通过在扭转之前施加的预压缩，将结构的坡印亭模量从初始负值编程为零和正值。我们的工作开辟了途径，编程材料的非线性弹性模量和合理的设计调整剪切和正常的反应之间的耦合。在超材料中获得反向和可编程的坡印廷效应激发了从设计机器材料、软机器人和致动器到工程生物组织、植入物和在压缩和扭转下发挥功能的假体设备的各种应用。
英文摘要：
The Poynting effect generically manifests itself as the extension of the material in the direction perpendicular to an applied shear deformation (torsion) and is a material parameter hard to design. Unlike isotropic solids, in designed structures, peculiar couplings between shear and normal deformations can be achieved and exploited for practical applications. Here, we engineer a metamaterial that can be programmed to contract or extend under torsion and undergo nonlinear twist under compression. First, we show that our system exhibits a novel type of inverted Poynting effect, where axial compression induces a nonlinear torsion. Then the Poynting modulus of the structure is programmed from initial negative values to zero and positive values via a pre-compression applied prior to torsion. Our work opens avenues for programming nonlinear elastic moduli of materials and tuning the couplings between shear and normal responses by rational design. Obtaining inverted and programmable Poynting effects in metamaterials inspires diverse applications from designing machine materials, soft robots and actuators to engineering biological tissues, implants and prosthetic devices functioning under compression and torsion.
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