Effect of infill parameters and thermal annealing on the mechanical behavior of FDM 3D-printed polymer

This study investigates the synergistic effects of printing parameters and thermal annealing on the mechanical performance of PLA and carbon‑fiber‑reinforced PLA (CF‑PLA). Using a full factorial design, the influence of infill pattern, density, and annealing temperature was evaluated. Results indicate that while the elastic modulus remains statistically insensitive to the investigated factors, the ultimate tensile strength (UTS) and hardness are predominantly governed by material type and infill density. Notably, thermal annealing at 95 °C facilitates a transition from brittle inter‑bead separation to a cohesive failure mechanism through molecular diffusion, significantly enhancing structural integrity. Unlike continuous‑fiber composites where path orientation is dominant, this work demonstrates that for short‑fiber systems, the interaction between infill geometry and inter‑bead coalescence is the primary driver of performance. These findings provide a robust framework for optimizing the durability of functional FDM components.