Mechanical performance and interlayer adhesion of multi-material 3D-printed PETG/PETG-carbon-fiber composites

3D-printed multi-materials are widely used in structural applications. However, variations in material properties can cause interlayer residual stresses, reducing overall part performance and often leading to defects such as warping, cracking, and delamination. In this study, the interlayer adhesion behavior of 3D-printed pure polyethylene terephthalate glycol (PETG) and 10wt% carbon fiber-reinforced PETG (PETG-CF) composites, fabricated via Fused Deposition Modelling (FDM), was investigated. Lap shear, flexural, and tensile tests were conducted to evaluate adhesion strength and stress distribution across the interfaces of PETG and PETG-CF layers for both annealed and unannealed specimens. The results indicate that annealing at elevated temperatures and longer durations significantly enhanced interlayer adhesion and mechanical strength. Microscopic analysis confirmed improved layer fusion in annealed specimens, characterized by reduced voids and delamination, indicating enhanced interlayer bonding. By optimizing annealing conditions, this study provides clear insights and suggests a pathway to improve the mechanical performance of multi-material 3D-printed components and reducing interlayer failures.