Vibrational and dynamic properties of PLA/GF composites influenced by the synergistic effect of infill geometry and density

Fused Filament Fabrication (FFF)-based PLA composites reinforced with short glass fibers offer enhanced mechanical properties and processability. However, their vibration response, dynamic mechanical behavior, and wear resistance remain underexplored, despite being critical for load-bearing and impact-sensitive applications. This study addresses that gap by evaluating the combined effects of infill geometry and density on the mechanical, vibrational, viscoelastic, and tribological performance of 3D-printed PLA/Glass Fiber composites. Three advanced infill structures, Cubic, Octet, and Cubic Subdivision, were tested at infill densities of 50%, 70%, and 90%, using seven experimental methods including free vibration and dynamic mechanical analysis (DMA). Results show the Cubic pattern yielded the highest tensile strength and modulus (24.65 MPa, 0.95 GPa), while the Octet pattern showed superior flexural stiffness and the highest natural frequency (41.5 Hz). The Cubic Subdivision pattern offered the best damping performance, with the highest Tan δ (3.35), loss modulus (985.2 MPa), and Tg (77.21°C). Wear resistance and hardness increased with infill density across all patterns. These insights demonstrate that optimized infill design significantly improves both structural and functional performance. The findings are directly applicable to lightweight, vibration-sensitive components such as drone frames, orthopedic implants, vehicle interiors, and protective equipment.