Bio-inspired self-stitching for enhancing ductility and impact resistance of unidirectional laminated composites

This paper innovatively proposed sandwich-type hybrid carbon fiber reinforced polymer (CFRP) laminates with continuous layers and discontinuous self-stitching layers. The self-stitching structure, characterized by nesting of adjacent layers, was inspired by the unique overlapping feature of ironclad beetle and brick-and-mortar feature of nacre. Three-point bending according to ASTM D7264 were performed using an universal testing machine and Charpy impact according to ISO 179-2 were performed using a Digital IZOD Impact tester to evaluate the mechanical performance. The self-stitching microstructure can significantly enhance the toughness and pseudoductility of CFRP laminates by promoting delamination and activating large scale fiber bridgings additionally. Compared with unidirectional CFRP, a well-designed hybrid laminates with self-stitching layers can simultaneously improve the flexural stiffness, energy absorption and failure strain by 9.1%, 81.5% and more than 228% under quasi-static bending conditions, respectively. Meanwhile, the dynamic energy absorption of the welldesigned hybrid laminate outperformed that of unidirectional CFRP by 66.5%. This work achieved a good trade-off between strength and toughness of CFRPs and provided a new way for the design of high-performance materials.