Influences of isothermal annealing post‐treatment on mechanical performances in fused deposition modeling manufactured short carbon fibrous PETG and PA composites

Fused deposition modeling (FDM) based large‐area additive manufacturing has advanced significantly, particularly for producing large parts with high‐performance short fibrous composites. To improve the mechanical performance of these manufactured parts, isothermal annealing is often employed as a post‐treatment for FDM‐produced components. Hence, this study examines the impact of isothermal annealing on the mechanical properties of short carbon fiber‐filled Polyamide 12 (PA12‐CF) and polyethylene terephthalate glycol (PETG‐CF). Samples are prepared using a customized high‐extrusion‐rate FDM (HFDM) system with varying key printing parameters (layer height and extrusion width). Three‐point bending tests are employed to assess the bending strength, modulus, and fracture deflection of the samples. Results show that annealing treatment significantly enhances the bending performance of PA12‐CF, with strength and modulus increasing by 27.8% and 31.2%, respectively. In contrast, PETG‐CF exhibits relatively minor improvements in bending strength (8.1%) and modulus (2.7%). Optical microscopy reveals that different printing parameters notably influence the alignment of short carbon fibers, affecting the mechanical properties, while the annealing treatment does not alter these parameter‐dependent trends. Finite element simulations further demonstrate that the presence of carbon fibers contributes to a progressive enhancement of the polymer matrix, which impacts mechanical improvement during annealing.