Structural design and mechanical protection performance of rod- type metamaterials: A review

With the increasing demand for lightweight and high-strength materials in aerospace, automobile manufacturing, and other fields, rod-type metamaterials have garnered significant attention owing to their programmable mechanical properties, high energy absorption efficiency, and multiscale design freedom, making them a research hotspot in the field of mechanical protection. This work systematically reviews three design categories: the single rod-type periodic microstructure design (including microstructural configuration, spatial geometry, and assembly methods), the hybrid rod-type periodic microstructure design (covering classical and novel composite strategies and key design features), and the hybrid aperiodic design (e.g., spatial arrangement, gradient distribution, and topology optimization). The mechanisms by which these methods influence mechanical performance (e.g., elastic modulus, compressive strength, and energy absorption efficiency) are analyzed. The results demonstrate that optimizing the microstructural cell topology, introducing gradient structures, and implementing multiphase composites can significantly enhance impact resistance and load-bearing stability while mitigating stress concentrations and geometric imperfections. Advances in additive manufacturing have enabled the precise fabrication of complex rod-type metamaterials. Potential applications in battery protection, heat sinks, orthopedic implants, and automotive buffers are discussed, providing theoretical and technological insights for function-oriented metamaterial design.