Tunable Auxetic Mechanical Metamaterials with Arch-Shaped Units

Rationally designed artificial materials providing unusual mechanical properties are attracting continuous interests due to the wide technological applications such as metamaterials for flexible electron and biomedical devices. A variety of natural biological tissues exhibit J-shaped stress-strain behavior, so a challenge and interesting subject is to offer protection to electronics from a certain strain that may induce potential device failures. In the current letter, a novel porous auxetic metamaterial with J-shaped stress-strain curve is designed and a method for tuning Poisson's ratio and stress-strain curve is illustrated. Experimental tests, numerical simulations, and analytical modeling are implemented to quantify the evolution of the Poisson's ratio and stress-strain curve, revealing the underlying mechanisms responsible for the unusual behavior. The structure simultaneously shows elastic wave bandgaps at certain frequency, which can finally extend to three-dimension. The designed structural metamaterial has potential for applications in tissue engineering, bio-medical devices, and comfortable integration of stretchable electronics with biological tissues, it also provides a new routine to design architected metamaterial systems exhibiting desired properties.