Design of multi-stable metamaterial cell with improved and programmable energy trapping ability based on frame reinforced curved beams

Curved beams are a class of elements capable of bi-stability and can be used to construct multi-stable metamaterials. These materials leverage elastic snap-through in curved beams to transition between multiple stable states, effectively achieving energy absorption and trapping. The elastic deformation allows the structure to be used repetitively. However, the conventional curved beam unit cells design process omits the influence of supporting frames, resulting in inadequate constrains of the beam in the fabricated metamaterials. Its mechanical properties and number of stable states can be significantly diverged from theoretical predictions. This paper presents a novel multi-stable metamaterial with improved and consistent energy trapping ability based on frame reinforced curved beams. Comparative finite element analysis of three unit-cell types demonstrates the superior bi-stability of the proposed cell. Moreover, parametric analysis reveals the proposed cell has a wider range of parameters that can achieve bi-stability. The mechanical properties of the single cell and the 2 x 2 metamaterial are obtained by compression tests. The results validate the linear mechanical response that correlates with the number of unit cells which allows optimal programming of multi-stable metamaterials. Finally, plate impact test is conducted to investigate and analyze the cushioning performance of the multi-stable metamaterial.