Modular metamaterials with strong auxeticity, tunability and crashworthiness

Abstract

The properties of existing auxetic materials cannot be tuned once after manufacture, and their auxeticity is commonly weakened at large deforming degree. To break these limits, modular metamaterials are proposed to combine strong auxeticity, tunability and crashworthiness, which can be flexibly assembled and arbitrarily 3D expanded only using same small-size chiral units, enabling the conveniences in manufacture, transportation, storage, assemble, etc. The modules can thus be on-demand disassembled and reorganized to tune the stiffness distribution and mechanical properties to adapt to complex protective requirements. For instance, they can be specially assembled with stiffness gradient to customize the mechanical response, or can be hybrid and randomly assembled to quickly respond to emergencies without affecting the crashworthiness. Based on experimental and simulation results, the modular metamaterials deform stably and uniformly with firm interlocking capability under crush loads, and present significantly stronger and larger-range auxeticity than traditional integrated auxetic materials. More critically, they possess superior mechanical robustness under various crush velocities and the structural scales. On this basis, parametric study is carried out to further improve the comprehensive performance. Despite specific energy absorption and energy absorption efficiency of the optimal metamaterial are respectively 6.33 % and 23.58 % smaller than classical auxetic material of same mass, its effective Poisson’s ratio and force efficiency are respectively 6.67 % and 329.8 % larger, and thus they can be seen as a potential candidate for protective devices. This work provides a novel strategy for designing auxetic materials, and opens a new avenue on improving specific functions of the mechanical metamaterials.