Chiral multi-curved shell metamaterials integrating compression-torsion and buckling mechanisms for ideal energy absorption.

Metamaterials with compression-torsion or buckling mechanism have demonstrated significant potential for energy absorption. However, compression-torsion metamaterials easily trigger deformation, resulting in low load-bearing capacity, and buckling ones have high peak load with fluctuations, accompanying severe localized deformations. Here, we propose chiral multi-curved shell (CMCS) metamaterials that synergistically couple compression-torsion and buckling mechanisms, achieving high and smooth load curves. The compression-torsion mechanism enables metamaterials to convert compressive deformation into torsional deformation, preventing abrupt changes in local geometry. Simultaneously, the synergy of compression-torsion and curved shell ensures that the buckling provides high load-bearing capacity and avoids localized deformation. This coupled compression-torsion-buckling deformation enables the material to achieve high energy storage. Characterized by tests, the CMCS metamaterials exhibit enhanced energy absorption and tuneability. Compared with Kresling and hexagon metamaterials, the proposed design achieves a 20-fold higher specific energy absorption (SEA) and a 50% higher efficiency of energy absorption (EEA) owing to its higher and gentler plateau phase, respectively. Multiple drop tests demonstrate their reliable impact protection and reusability. CMCS metamaterials provide a novel concept for lightweight and high-strength protective structures or materials.