Influence of post-heat treatment on the internal microstructure and mechanical behavior of 3D printed carbon fiber-reinforced PLA
The mechanical properties of components manufactured via fused filament fabrication (FFF) are significantly influenced by defects that occur during printing and post-processing conditions. This study thoroughly investigated the effects of post-heat treatment on the internal microstructure and mechanical properties of 3D-printed polylactic acid (PLA) reinforced with short carbon fibers (PLA–CF). Samples were produced using FFF and subsequently annealed at 50 and 120 °C for 2 h. X-ray microscopy (XRM) was employed to assess the internal defects, void distribution, and microstructural changes at both the macro and micro levels resulting from the heat treatment. XRM volume segmentation revealed that voids decreased steadily as the treatment temperature increased. The untreated samples had a solid-to-void ratio of 56.205%. The sample treated at 50 °C had a ratio of 56.72%, and the sample treated at 120 °C had a solid-to-void ratio of 58.922%. Mechanical testing adhered to ASTM D638 standards, and the experimentally determined geometries were used in finite element analysis models to confirm the thermomechanical responses. The findings revealed that annealing improved the tensile strength and ductility by enhancing interlayer bonding and reducing porosity while preserving material toughness. These results highlight the significance of controlled heat treatment in optimizing the performance of FFF-printed PLA–CF composites and demonstrate the value of incorporating XRM-informed geometries into computational models for accurate-performance prediction.