Synergistic strengthening and toughening of 3D-printed PEEK-CF/PEEK heterostructures via anisotropy regulation and bioinspired interfacial interlocking

Polyether ether ketone (PEEK) and carbon fiber reinforced PEEK (CF/PEEK) are vital for extreme environments such as aerospace, yet anisotropic behavior and interfacial failure mechanisms of PEEK-based heterostructures remain poorly understood. This study utilizes high-temperature dual-nozzle fused filament fabrication (FFF) to develop PEEK, CF/PEEK, and PEEK-CF/PEEK heterostructures. The work delivers three main innovations: (i) systematic elucidation of anisotropy-dependent mechanical responses of heterostructures under multiple loading modes, linking macroscopic damage evolution to microscopic fracture characteristics; (ii) quantitative validation of the stiffness-toughness synergy in representative aerospace thin-walled structures including cylindrical shells and honeycomb panels; and (iii) seamless integration of bioinspired mechanical interlocking textures into the FFF process to directly reinforce heterogeneous interfaces. Along the primary deposition direction, the heterostructures exhibit synergistic strengthening and toughening, achieving a tensile strength of 86.1 MPa and a modulus of 2.48 GPa, surpassing neat PEEK, while maintaining an 8.29% elongation at break, significantly higher than CF/PEEK. Radial compressive stiffness of the cylindrical shell increased by 86.0% over PEEK, while axial recovery improved by 31.8% relative to CF/PEEK. The bioinspired interfacial interlocking strategy enhanced interfacial strength by 28.8%, with microscopic analysis confirming a transition from abrupt brittle fracture to progressive damage evolution. These findings provide a robust strategy for manufacturing structurally optimized, mechanically tailorable PEEK heterostructures for extreme environments.