Synergistic regulation of carbon fiber orientation and mechanical anisotropy by the FGF shear flow field

During the fused granulate fabrication (FGF) of fiber-reinforced thermoplastic composites, fibers preferentially align along the flow direction, leading to significant mechanical anisotropy. This restricts their use in high-performance, multiaxial load-bearing structures and has become a major bottleneck in the development of FGF for high-end manufacturing. To overcome this challenge, a shear screw (SS) with integrated shear-inducing elements was developed. Structural parameters were optimized using a simulation-experimental approach, allowing precise control of carbon fiber orientation. The results show that, compared to a conventional screw (CS), the SS promotes a helical carbon fiber orientation, significantly reducing mechanical property differences between orthogonal printing directions. The anisotropy index decreases from 0.46 to 0.16, showing a marked improvement in anisotropic properties. Additionally, the SS simultaneously optimizes crystallization behavior, resulting in notable improvements in tensile strength and stiffness. This work offers an efficient screw design solution for producing high-performance, low-anisotropy composites via FGF. Leveraging shear modulation to induce helical fiber orientation effectively mitigates mechanical anisotropy, which is crucial for accelerating the large-scale adoption of these composites in advanced manufacturing sectors, such as aerospace and automotive.