Programming Sequential Twist–Buckling and Fracture in Metamaterials via Hetero-chiral Design

This study presents a hetero-chiral metamaterial leveraging two helical angles to synergistically enhance strength, and toughness — thereby overcoming the typical trade-off among these properties. Under compression, the 3D-printed optimal hetero-chiral structure exhibited a 3.4-fold increase in stiffness, a 2.2-fold increase in strength and a 1.6-fold increase in toughness over its homo-chiral counterpart. Deformation tracking, fracture imaging and finite element analysis reveal that these improvements stem from a multi-stage failure mechanism, initiated by the fracture of small-angle helical rods under compressive-bending-buckling, followed by the engagement of large-angle helical rods which undergo energy-dissipating bending–twist–buckling. This sequential behavior redistributes stress and suppresses catastrophic failure, thereby improving load-bearing capacity and energy dissipation. Our findings validate a functional heterogeneity approach for designing high-performance mechanical metamaterials suitable for protective equipment and energy-absorbing applications.