Planar metamaterial with sign-switching Poisson's ratio based on self-contact slits

The emergence of artificial metamaterials not only enables many physical and mechanical properties that are not accessible by natural materials but also provides people with new opportunities to break down particular limitations in engineering. In this work, a new metamaterial characterized by unusual sign-switching Poisson's ratio is introduced. Different from all conventional and auxetic materials that exhibit reversed lateral deformation under tension and compression, the new metamaterial proposed here always expands in the direction orthogonal to the applied load. Our design relies on a planar construction perforated with periodically distributed selfcontact slits. The mechanical responses of the proposed metamaterial subjected to uniaxially tensile, compressive, and bending loads are systematically investigated using a combination of numerical simulations and experimental tests. It is found that a lateral expansion effect is also induced for the bending test. Based on its unique property, a new concept of implant is developed to reduce the risk of loosening after total hip replacement. The demonstrative example highlights the potential applications of the new metamaterial in various fastening systems.