A strategy for improving negative-Poisson's-ratio constraint effect and shape accuracy of metamaterials by regulating mechanical properties of elastomer with facile filler incorporation

Negative Poisson's ratio (NPR) metamaterials are widely used for their light weight and good shear resistance. However, the essential concave hollow structures in NPR materials may easily distort irregularly when the constraint effect of their solid materials is weak, especially for elastomer-based materials. Here, we introduced nano-scale carbon black (CB) particles into the NPR material based on thermoplastic polyurethane (TPU) elastomers to control the static and dynamic mechanical deformation behavior of the material, improving their constraint effect on the NPR structure. The results show that the modulus of the NPR structure is improved by 269% by adjusting the unit and rigid particle load. The Poisson's ratio of the NPR structure reaches as great as -1.3 via controlling the thickness/width ratio (TWR) of the unit. Meanwhile, finite element analysis verifies that when TWR is less than 0.5, increasing the modulus and yield strength of the composites can enhance the constraint on the NPR unit. Theoretical calculation shows that CB introduced into TPU can improve the shape accuracy of NPR structure. Therefore, the work could offer a new mechanical enhancing strategy for NPR materials, and its application potential is verified as a form of exoskeletons.