Crack modes and toughening strategies of bioinspired 3D printed double-helicoidal architectures

The crack modes and toughening strategies of 3D printed double-helicoidal (DH) composites were fully characterized by performing quasi-static three-point bending experiments and simulations. Notch-containing DH specimens were fabricated with dual-material curing 3D printer PolyJet technology, while single-helicoidal (SH) specimens were also prepared for comparison. The rigid glassy polymer VeroWhite and the soft rubbery polymer TangoBlackPlus were selected as the brick and adhesive of the specimens, respectively. First, the crack propagation path of the specimens under three-point bending loading was observed, and the fracture toughness and critical deformation displacements were calculated. The double twisting pattern of DH composite makes cracks deflect along complex deflection paths, resulting in increased energy dissipation required to produce deflected crack surfaces, which delays catastrophic damage. Then, the deformation and interlayer stress distribution under static loading were analyzed by finite element analysis. It was found that the interlaminar shear stresses I:513 and I:523 generated in adjacent layers were responsible for the crack deflection of the DH specimens. Toughening mechanisms of the DH structure inspired by coelacanth will promote the design of next generation fractureresistant composites.