Bio-inspired hierarchical metamaterials: cross-configuration shape optimisation for NPR retention and simultaneous stiffness-strength-energy absorption

The application potential of auxetic metamaterials in impact resistance and energy absorption has been widely studied. However, most research focuses on optimising a single performance of a single unit, struggling to balance the negative Poisson's ratio (NPR) effect and overall performance. Herein, this study for the first time integrates hierarchical design into auxetic configurations, fabricating bio-inspired hierarchical nested Ti–6Al–4V auxetic metamaterials via laser powder bed fusion (L-PBF). Combined with quasi-static compression simulations, experiments, and dynamic impact simulations, their properties, NPR effect, and protective performance are systematically evaluated. Validated finite element analysis explores the influence of key parameters in depth. Results show that the bio-inspired bamboo-like structure maintains a stable NPR effect, with specific stiffness, specific strength, and specific energy absorption increased by up to 252.5%, 130.7%, and 112.4% respectively. The maximum specific stiffness of the beam-lattice composite structure reaches 4.29 times that of traditional structures. Under impact speeds of 1–100 m/s, the bamboo-like structure exhibits smooth stress response and stable energy absorption characteristics. Through the ‘stress dispersion-interlayer expansion-fragment interlocking’ mechanism, it achieves the concurrent optimisation of stiffness, strength, energy absorption, and NPR effect, demonstrating application potential for impact-resistant and energy-absorbing components in the aerospace and automotive fields.