Balancing Strength and Flexibility: Mechanical Characterization of Carbon Fiber-Reinforced PLA Composites in FDM 3D Printing

Fused Deposition Modeling (FDM) is a commonly used 3D printing process characterized by its versatility in material selection; however, FDM’s layer-by-layer process often leads to lower strength properties. This study explores the mechanical properties of FDM 3D-printed composite materials printed with varying nozzle diameters, specifically on the influence of Carbon Fiber-reinforced Polylactic Acid (PLA-CF) on tensile and flexural strength when reinforcing Polylactic Acid (PLA) parts. Composite samples were printed with varying ratios of PLA and PLA-CF, ranging from 0% to 100% PLA-CF in 20% increments, with layer groups stacked vertically, while also using three different nozzle diameters (0.4 mm, 0.6 mm, and 0.8 mm). Tensile testing revealed a proportional increase in strength as PLA-CF content increased, indicating that carbon fiber reinforcement significantly enhances tensile performance. However, flexural testing demonstrated a decrease in bending strength with higher PLA-CF content, suggesting a trade-off between stiffness and flexibility. Mid-range ratios (40–60% PLA-CF) provided a balance between tensile and flexural properties. Finally, atomic force microscopy was utilized to provide a better understanding of the microscale morphology and surface properties of PLA and PLA-CF thin films. The results highlight the potential of PLA-CF/PLA composites to allow for more direct control over the tensile–flexural trade-off during the printing process, as opposed to manufacturing filaments with fixed fiber percentages. These results provide a path for tailoring the mechanical behavior of printed parts without requiring specialized filaments.