Crack twisting in hierarchical chiral structures

Numerous biological composites exhibit superior mechanical properties owing to their intricate hierarchy of chiral structures. Nonetheless, the mechanisms underlying the toughening of hierarchical chiral structures remain enigmatic. In this paper, we present a fracture mechanics model for the biological composites featuring a hierarchical chiral structure, aiming at elucidating the twisting behavior of crack and its corresponding toughening impact. We meticulously investigate the effects of chirality of structure elements at various levels on the energy release rate. The theoretical analysis reveals that by the fine-tunning chirality across multiple levels, the hierarchical chiral structure induces a discernible reduction in the energy release rate during crack propagation in a twisted way, significantly bolstering fracture toughness of biological composites. This study provides novel insight into the structure–property relationship of biological materials.