Mechanical design and analysis of bio-inspired reentrant negative Poisson's ratio metamaterials with rigid-flexible distinction

Aiming at achieving tunable reentrant structures with rigidity and uniformity, respectively, the C-shaped and S-shaped reentrant metamaterials were proposed by the bionic design of animal structures. Utilizing beam theory and energy methodology, the analytical expressions of the equivalent elastic modulus of the metamaterials were derived. Differences in deformation modes, mechanical properties, and energy absorption capacities were characterized by using experiments and the finite element analysis method. The effects of ligament angle and thickness on the mechanical characteristics of two novel metamaterials were investigated by using a parametric analysis. The results show that the stiffness, deformation mode, stress-strain curve, and energy absorption effects of three metamaterials are significantly different. This design philosophy can be extended from 2D to 3D and is applicable at multiple dimensions.