Improving bending and interlayer properties of hybrid-fiber-reinforced composites through functionally graded hybrid strategy by 3D-printing manufacturing process

To improve the bending and interlayer properties of hybrid-fiber-reinforced composites (HFRCs), a functionally graded hybrid (FGH) strategy is proposed inspired by the graded structure of bamboo. Specimens were prepared by utilizing the continuous-fiber 3D-printing manufacturing process, achieving graded changes in the fiber content and properties of the composites between and within layers. The differences in the mechanical properties and failure mechanisms of traditional interlayer HFRCs (IHFRCs) and functionally graded HFRCs (FGHFRCs) were comparatively analyzed. The mechanical-property test results demonstrated that the FGH strategy can further improve the mechanical properties of HFRCs. Compared with those of the IHFRCs, the bending strength and interlayer shear strength of the FGHFRCs increased by a maximum of 25.95 % and 41.20 %, respectively. Macro-micro fracture morphology analysis revealed that the interlayer hybrid led to a risk of delamination failure. However, the FGH effectively reduced the interlayer performance differences, changed the direction of crack propagation along the interlayer, and effectively suppressed the generation of delamination damage, which was conducive to further improving the properties of HFRCs. Owing to their enhanced properties and positive hybrid effect, the manufacturing process and the FGH strategy have considerable potential in engineering applications.