Novel multifunctional negative stiffness mechanical metamaterial structure: Tailored functions of multi-stable and compressive mono-stable

Negative stiffness (NS) mechanical metamaterials have excellent application prospect in a broad range of fields such as energy trapping, repeated energy absorption and so on. Although various kinds of NS mechanical metamaterials have been proposed, one configuration cannot simultaneously achieve multi-stability and mono-stability. This paper presented a novel multifunctional NS mechanical metamaterial structure, which possessed tailored functions of multi-stable and compressive mono-stable state without geometrical parameters adjustment. The novel multifunctional NS mechanical metamaterial structure with a conical shape consisted of both soft and hard material part and was fabricated by additive manufacturing technology. NS behaviors were achieved by the instability of the soft counterpart. Mechanical performance of this novel multifunctional NS mechanical metamaterial structure under axial compression was experimentally and numerically investigated. Influences of geometrical parameters tailoring stable state were systematically investigated and the ratio of offset distance, tilt angle, slenderness were found the key factors. Effective methods to make sure the tri-layer metamaterial structure achieving multi-stable after unloading from completely compacted state were proposed.