Recent advances in reinforced honeycomb mechanical metamaterials: a review

Honeycomb structures, as a class of ultra-lightweight mechanical metamaterials, achieve their exceptional mechanical performance predominantly through the carefully engineered geometry of their cellular architecture, rather than solely through the intrinsic properties of the constituent materials. While the intrinsic mechanical properties of the base material—such as stiffness and strength—also influence the overall response, their contribution is generally secondary to that of the structural configuration. This review systematically summarizes the major advancements in honeycomb structure design, with a focus on reinforced two-dimensional geometric configurations aimed at developing new cellular architectures with diversified and optimized mechanical properties. The paper first revisits the classical honeycomb topologies, then discusses the crashworthiness of traditional concave hexagonal honeycombs and their common improvement strategies. Furthermore, a clear classification framework is established according to design scale. Reinforced macroscopic designs are categorized into hierarchical, graded, curved, foam-filled, hybrid, and symmetric/asymmetric configurations. The review also explores the influence mechanisms of critical loading parameters and geometric characteristics, along with a summary of mainstream manufacturing techniques and their practical applications. Finally, the paper highlights key design trends and future challenges in improving the mechanical performance of honeycomb structures, providing insights into advancing collision safety and structural resilience.