Mechanical Performance of Functionally Graded Carbon Fiber-Reinforced PLA Composites Fabricated via Multi-Material FDM

In this study, the mechanical performances of carbon fiber (CF) reinforced polylactic acid (PLA) composites produced using the multi-material FDM (Fused Deposition Modeling) method were investigated. Single-, two-, and three-layer configurations were fabricated using pure PLA, 5% carbon fiber-reinforced PLA (5CF), and 10% carbon fiber-reinforced PLA (10CF) filaments. Dimensional accuracy analyses showed that high geometric precision within ±0.1 mm was achieved for all specimens. The mechanical performance of the two-layer structures was higher compared to single-layer structures. The two-layer structure with a bottom layer of pure PLA and a top layer of 5% CF-PLA showed a 19% improvement in tensile strength, a 74% improvement in elastic modulus, and a 24% improvement in flexural strength (2T-5CF). The three-layer (PLA/5% CF/10% CF) hybrid structure provided a 65% increase in elastic modulus and a 4.2% increase in flexural strength compared to pure PLA (3T). However, the flexural strength of the 3T configuration (69.17 MPa) remained below that of the single-layer 5CF (78.08 MPa) and 10CF (70.71 MPa) specimens, indicating that the three-layer arrangement offers no flexural strength advantage over single-layer CF-reinforced structures despite its gradient character. The fracture surfaces were examined using scanning electron microscopy (SEM) to evaluate interlayer transition regions and possible separations. The results reveal that the interaction of layer alignment and fiber ratio plays a decisive role in shaping the mechanical performance in functionally graded (FGM) carbon fiber reinforced PLA composites produced by the multi-material FDM method.