The Role of Carbon Fibers in FFF 3D Printed Composites: A Comprehensive Review on the Effect on Mechanical Properties, Fracture Toughness, and Tribological Performance.

Polymeric composites reinforced with short or continuous carbon fibers offer exceptional mechanical and tribological properties that outperform their unfilled counterparts. The combination of these excellent properties with the possibility to manufacture custom-made composites with complex shapes and geometry is unique; therefore, additive manufacturing has recently emerged as an intriguing manufacturing technique combining these two features. Specifically, Fused Filament Fabrication (FFF) has attracted significant academic and industrial attention owing to its operational simplicity, cost-effectiveness, and compatibility with a wide range of thermoplastic matrices. This review provides a comprehensive overview of FFF-printed carbon-fiber reinforced composites, focusing on strategies to optimize both their mechanical and tribological properties. The first part introduces the core aspects of FFF technology and highlights how the printing process is altered by the incorporation of carbon fibers. The central part systematically points out the benefits of utilizing short or continuous carbon fibers on the mechanical and tribological performance of the composites. The final section addresses advanced post-processing techniques designed to mitigate typical printing issues, followed by an analysis of current research trajectories. Overall, this review examines the current literature to provide a state-of-the-art summary, highlighting the manufacturing possibilities, inherent limitations, and new research frontiers of FFF-printed carbon fiber-reinforced polymer composites.