Experimental investigation and optimization of fused filament fabrication parameters for enhanced mechanical performance of PETG and carbon fiber-reinforced PETG composites

This study investigates the influence of key additive manufacturing parameters on the mechanical performance of polyethylene terephthalate glycol (PETG) and carbon fiber-reinforced PETG (CF-PETG) composites fabricated through fused filament fabrication (FFF). Eighteen specimens were printed with varying infill densities (50%, 75%, 90%), infill patterns (gyroid, cubic, triangle), printing speeds (40–50 mm/s), and layer thicknesses (0.1–0.3 mm). Mechanical testing showed that CF-PETG printed at 90% infill, triangular pattern, 45 mm/s speed, and 0.1 mm layer thickness achieved superior compressive strength, recording 47.21 MPa at 10% and 61.56 MPa at 50% deformation-a 42% improvement over the best PETG counterpart. Flexural strength of CF-PETG printed at 75% infill, cubic pattern, 50 mm/s, and 0.1 mm layer thickness increased by 23%, reaching 59.2 MPa, while tensile strength gains remained marginal. In contrast, PETG printed at 90% infill, triangular pattern, 45 mm/s, and 0.1 mm layer thickness exhibited higher impact strength (2.55 kJ/m 2 ) than CF-PETG (1.44 kJ/m 2 ), reflecting a stiffness–toughness trade-off. Design of Experiments analysis identified infill density as the most influential factor for both materials. PETG performance improved with increasing infill and pattern complexity, whereas CF-PETG reached optimal properties at moderate speeds and simpler patterns, likely due to sensitivity in fiber dispersion and matrix bonding. Interaction plots showed that parameter combinations significantly affect tensile and flexural behaviour, with CF-PETG exhibiting more irregular responses due to complex fibre–matrix interactions. Optimization using desirability functions produced composite desirability values of 0.8518 for PETG and 0.9872 for CF-PETG, confirming the superior performance potential of fibre-reinforced systems when appropriately tuned. Overall, carbon fiber reinforcement enhances mechanical properties, especially compression and modifies process-property relationships, requiring more precise control of FFF parameters for structural applications.