Harnessing out-of-plane deformation to design 3D architected lattice metamaterials with tunable Poisson's ratio.

Auxetic materials exhibiting a negative Poisson's ratio are of great research interest due to their unusual mechanical responses and a wide range of potential deployment. Efforts have been devoted to exploring novel 2D and 3D auxetic structures through rational design, optimization, and taking inspiration from nature. Here we report a 3D architected lattice system showing a negative Poisson's ratio over a wide range of applied uniaxial stretch. 3D printing, experimental tests, numerical simulation, and analytical modeling are implemented to quantify the evolution of the Poisson's ratio and reveal the underlying mechanisms responsible for this unusual behavior. We further show that the auxetic behavior can be controlled by tailoring the geometric features of the ligaments. The findings reported here provide a new routine to design architected metamaterial systems exhibiting unusual properties and having a wide range of potential applications.