Fig. 3: Fracture toughness improvements by strategically designing the stacking sequence of nature-inspired architecture.

a Alternate layup stacking configuration of the modified isotropic architecture showing the αβγ stacking sequence with respect to the shift position and specific orientation of the granular domains. b, c Tomographic images of the fracture surfaces. Straight-through failure of the pure filament sample (b). Complex post-fracture surface and extended crack profile images of composite architecture showing damage tolerance and fracture resistance driven by the αβγ stacking sequence effect (c). d Anisotropic approximation graph showing stiffness differences in local and global regions between pure PLA and BF/PLA composite architectures. e Extended tomography images of the region of interest (e) in Fig. 3c showing details of inter- and intra-granular crack propagation in the α top, β middle, and γ bottom layers, respectively. Individual granular domains were identified according to local fiber orientation and then segmented into 30° (yellow), 90° (red), and 150° (blue) hexagonal regions. The schematic images provide detailed descriptions of crack propagation types. f Extended images of the region of interest (f) in Fig. 3c Increased width of the crack arrow indicates increased crack driving force. g L-D curves of pure and composite filaments. SEM shows severe crack bridging and pullout of the transverse fibers. h Step-like rising R-curve showing fracture toughness with accompanying continuous crack arrest and crack propagation. The gray shaded region shows the shape of the R-curve macroscopically. i, j Comprehensive comparison of tensile modulus and fracture energy of pure and composite architectures. Tensile modulus (E) and Fracture energy (G) are presented as mean values ± SD, n = 5 independent samples. Source data are provided as a Source Data file.