Large recoverable elastic energy in chiral metamaterials via twist buckling

Mechanical metamaterials with high recoverable elastic energy density, which we refer to as high-enthalpy elastic metamaterials, can offer many enhanced properties, including efficient mechanical energy storage1,2, load-bearing capability, impact resistance and motion agility. These qualities make them ideal for lightweight, miniaturized and multi-functional structures3–8. However, achieving high enthalpy is challenging, as it requires combining conflicting properties: high stiffness, high strength and large recoverable strain9–11. Here, to address this challenge, we construct high-enthalpy elastic metamaterials from freely rotatable chiral metacells. Compared with existing non-chiral lattices, the non-optimized chiral metamaterials simultaneously maintain high stiffness, sustain larger recoverable strain, offer a wider buckling plateau, improve the buckling strength by 5–10 times, enhance enthalpy by 2–160 times and increase energy per mass by 2–32 times. These improvements arise from torsional buckling deformation that is triggered by chirality and is absent in conventional metamaterials. This deformation mode stores considerable additional energy while having a minimal impact on peak stresses that define material failure. Our findings identify a mechanism and provide insight into the design of metamaterials and structures with high mechanical energy storage capacity, a fundamental and general problem of broad engineering interest.