Multi-walled design and crushing failure of 3D-printed continuous fibre reinforced composite structure with negative Poisson’s ratio effect

Composite additive manufacturing enables freeform fabrication of complex structures, while multi-walled structures offer excellent mechanical properties. Herein, composite star-shaped multi-walled structures with tuneable inner/outer angles are fabricated via in situ impregnation 3D printing. Quasi-static crushing tests and finite element simulations investigate how structural parameters affect deformation, energy absorption and failure modes. Results show that the outer angle dominates initial failure mode and load-bearing capacity, while the inner angle regulates the secondary load-bearing stage. Two distinct failure mechanisms are revealed that the outward deformation mode, with an internal pull-back effect, enables a stable secondary energy absorption stage. The specimen with 150° inner angle achieves a secondary peak load 2.9 times the initial value. By contrast, the inward deformation mode induced by coordinated negative Poisson’s ratio (NPR) effect weakens this capacity. A targeted reinforcement strategy further suppresses unstable deformation and improves plateau stress in the modified R-1 structure.