Double-stage gear cluster-enabled metastructure for multi-magnitude continuously tunable stiffness

• A double-stage gear-based metastructure is proposed for stiffness tuning. • It enables wide-range rapid and narrow-range precise stiffness adjustment. • The Young’s modulus adjustment range of the unit cell spans 3 orders of magnitude. • The continuous tunability of the metastructure is independent of base materials. The development of gear-based stiffness-tunable mechanical metamaterials provides a reliable technical approach for the adaptive and continuous adjustment of structural stiffness under different working conditions. However, continuously and precisely regulating wide-range stiffness spanning multiple orders of magnitude while ensuring structural integrity remains a challenge. To address this limitation, a novel metastructure enabled by a double-stage gear cluster is proposed. This design leverages the coordinated rotation of primary and secondary gear frames to dynamically redistribute internal forces within the unit cell, enabling fast coarse tuning and precise fine tuning of stiffness within an ultra-wide-range. The metastructure was fabricated using stereolithography from polymer resin, and its mechanical behavior was systematically studied through extensive finite element analysis (549 distinct configurations) and quasi-static compression experiments. Remarkably, it exhibits a continuously tunable compressive Young’s modulus spanning three orders of magnitude (10 -1 to 10 1 MPa), achieving an adjustment range of 109.2 times. Further, the double-stage gear metastructure has an adjustment range of more than 60 times. Sustainable tensile modulus tunability was also demonstrated. Different materials can be used to fabricate this metastructure, satisfying various stiffness span requirements. This work establishes a robust pathway for designing highly adaptable mechanical metastructures, enabling wide-range rapid stiffness adjustment and narrow-range precise fine-tuning as requirements.