Z-direction performance and failure behavior of 3D printed continuous fiber reinforced composites with sinusoidal structure

The 3D printing process for continuous fiber reinforced composites (CFRCs) has many benefits, but it still faces an unsolved issue: poor performance in the Z-direction (through-thickness). To address this problem, a novel Z-direction enhancement method was proposed to optimize the fiber arrangement in the Z-direction within parts by altering the in-plane structure and out-of-plane configuration of CFRCs. Based on the bioinspired structural design and the 7-axis 3D printing robot, the sine-surface-layered CFRCs (Sin-CFRCs) were fabricated. Then, the Z-direction load-bearing capacity of Sin-CFRCs was characterized by the short-beam shear test and the three-point bending test, and the effect of structural parameters on the Z-direction performance were further examined. Moreover, Z-direction enhancement mechanisms were summarized by studying the mechanical behavior and the fracture mechanism. Finally, the results revealed a substantial improvement in the Z-direction performance of Sin-CFRCs compared to plane-layered CFRCs. The interlayer shear strength (ILSS) increased by 51.7% from 18.5 MPa to 28.1 MPa, and the flexural modulus rose by 22% from 13526 MPa to 16506 MPa. Moreover, the flexural fracture energy showed a significant improvement of 126%. These enhancements in performance can be attributed to the force field redistribution and the multiscale periodic modulus mismatch of Sin-CFRCs. As a result, the Z-direction load-bearing capacity and the energy absorption capability of Sin-CFRCs were significantly enhanced. This research opens up new possibilities for enhancing the Z-direction performance or even controlling the anisotropy of 3D printed CFRCs.