Abstract
Current designs of artificial metamaterials with giant Poisson’s ratios proposed microlattices that secrete the transverse displacement nonlinearly varies with the longitudinal displacement, and the Poisson’s ratio depends on the applied strain (i.e., tailorable Poisson’s ratio). Whereas metamaterials with tailorable Poisson’s ratios would find many important applications, the design of a metamaterial with a giant Poisson’s ratio that is constant over all the material deformation range has been a major challenge. Here, we develop a new class of bimaterial-3D-metamaterials with giant and strain-independent Poisson’s ratios (i.e., Poisson’s ratio is constant over the entire deformation range). The unit cell is 3D assembled of hinged-struts. Specially designed spherical hinges were utilized to give constant Poisson’s ratios. This new class of metamaterials has been demonstrated by means of experimental and numerical mechanics. 15 material samples were 3D printed by Stereolithography (SLA) and tested. We revealed a robust anisotropy dependence of the Poisson’s ratio. A giant negative Poisson’s ratio of −16 was obtained utilizing a highly anisotropic unit cell of dissimilar materials and stiffnesses. Materials with giant and strain-independent Poisson’s ratios provide a new class of artificial metamaterials, which would be used to optimize the performance of many existing devices, e.g., strain amplifiers and gauges.
Highlights
Artificial metamaterials are multiscale materials with exceptional macroscopic behaviors arising from the design of their microstructures beyond those of conventional materials found in nature[1,2]
In the case that E2 > E1, the distance between hinges 5 and 6 decreases while the distance between hinges 3 and 4 increases due to a unit cell stretching along x− axis (Fig. 1(c))
Νxz is positive while νxy is negative. Both νxy and νxz are positive, when the unit cell is made of identical struts (E1 = E2)
Summary
Artificial metamaterials are multiscale materials with exceptional macroscopic behaviors arising from the design of their microstructures beyond those of conventional materials found in nature[1,2]. Metamaterials of cubic symmetric 3D-unit cells with special topologies that promote microstructural buckling can give auxetic behaviors; i.e., an auxetic metamaterial is a material with a negative Poisson’s ratio[7]. An early study revealed a giant Poisson’s ratio of −12 for a microporous foam of an open network of crosslinked-anisotropic disc-shaped particles of expanded polytetrafluoroethylene[22]. A material with a tailorable Poisson’s ratio is preferred to be implemented over a specific strain range. Materials with strain-independent (i.e., constant) and giant Poisson’s ratios are required for making strain amplifiers. For the material design and implementation purposes, the Poisson’s ratio would be required to be constant over a wide range of applied strains. The new class of metamaterials developed here will find a wide range of applications that require materials with constant properties over a wide range of the material deformation, e.g., strain amplifiers
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