Tough Nature-Inspired Helicoidal Composites with Printing-Induced Voids

Exoskeletons of Odontodactylus japonicas, the "smasher-type" mantis shrimp, feature a raptorial appendage comprising a Bouligand architecture of chitin nanofibrils with newly observed voids or defects between the polysaccharide α-chitin and protein interfaces. Here, we use a continuous-fiber 3D printing technology to simulate such materials in carbon fiber-reinforced (helicoidal) composites, complete with the presence of voids due to imperfect printing. The specific impact energies of the 3D printed helicoidal composites are clearly superior and further enhanced by the presence of the voids. To explain the role of the Bouligand architecture, interlaminar stresses are computed and found to yield anti-delamination characteristics, and a theoretical model is derived to evaluate the optimal helicoidal architecture. Finite element modeling indicates that the voids tend to deform and coalesce on loading and appear to guide the fracture into the formation of an ideally twisted crack in the printed helicoidal composites, thereby contributing to the impact toughness.