Mechanical properties and damage failure of 3D-printed continuous carbon fiber-reinforced composite honeycomb sandwich structures with fiber-interleaved core

Sandwich structures with good mechanical performance can be manufactured by continuous carbon-fiber-reinforced composites (CCFRC) via the fused filament fabrication (FFF) technology. Poor inter-thread bonding is a major reason for the failure of these sandwich structures. In the present study, a novel fiber-interleaved printing pattern has been proposed to improve the bonding property between printing threads. And panel/core integrated sandwich structures were fabricated via the FFF technology. The manufacturing quality was examined by microscopic examination and non-destructive computed tomography (CT) scanning. The results indicated that manufacturing voids are mainly concentrated in the printed carbon fiber bundles, resulting from inadequate infiltration between the reinforcement and the matrix. Flatwise compression tests were conducted to compare the mechanical performance of sandwich structures with the fiber-adjacent and fiber-interleaved core. The results clearly demonstrated that the fiber-interleaved design can significantly improve the mechanical performance of the sandwich structures (i.e., 44% higher in elastic modulus and 119% higher in strength). Furthermore, three-point bending tests were conducted to investigate the flexural behavior. Fractographic analysis demonstrated that the main failure modes under these loading conditions include fiber pull-out and breakage, delamination, local core crushing, fiber/matrix and panel/core debonding.