Hinged-3D metamaterials with giant and strain-independent Poisson's ratios

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.