Hybrid structural design for 2.5D continuous fiber-reinforced lattice composites with enhanced out-of-plane bending performance

Continuous fiber-reinforced polymer additive manufacturing (CFRP-AM) is emerging as a promising alternative to conventional fabrication of continuous fiber-reinforced lattice structures (CFRLSs), offering greater design flexibility and enhanced mechanical performance. However, most existing CFRLS designs are typically simple and limited to two-dimensional forms, leaving the full potential of CFRP-AM for improving mechanical performance, particularly bending performance, unexploited. This work introduces a novel structure design strategy for CFRP-AM to construct two-and-a-half dimensional (2.5D) hybrid CFRLS with superior out-of-plane bending performance by rationally combining load-specific lattice designs to harness the fiber tensile strength. This strategy partitioned CFRLS panels into compression/tension sides, followed by deploying load-specific lattices to accommodate the localized stresses: a stretch-dominated configuration on the compression-side for superior compression performance, and a unidirectional structure with bracing on the tension-side that exploits the anisotropy of the fiber composite for enhanced tensile performance. Three-point bending tests, alongside finite element modeling and analytical models, are employed to investigate their bending behavior, failure mechanisms, and performance customization strategies. The results show that the developed 2.5D CFRLS panel demonstrates superior out-of-plane bending performance while remaining lightweight, with its specific out-of-plane bending strength achieving a remarkable 45.0% to 90.0% improvement over reported designs of CFRLSs for CFRP-AM.