Effects of Hygrothermal Aging on Microstructure and Tensile Strength in 3D Printed Carbon Composites

This work explores the impact of hygrothermal aging on the structural changes and tensile properties of specimens from short carbon fiber reinforced PA6 matrix with and without continuous carbon fiber reinforcement, manufactured using fused filament fabrication (FFF). The study reveals that environmental factors like humidity can affect the material properties of polymer composites, causing a hygroscopic swelling which leads to specimen warpage and ultimately, a reduction in tensile strength. For this purpose, tensile test specimens were produced and conditioned by hygrothermal aging at 60 °C and 90% humidity for five weeks. Subsequently, micro- and macro-structural changes were analyzed by X-ray computed tomography as well as tensile experiments were performed. Results showed that because of the non-uniform porosity distribution in FFF specimens, hygrothermal aging leads to increased warpage in all specimens, with more pronounced curvatures observed in specimens without continuous fiber reinforcement. However, the conditioning resulted in the degradation of the fiber-matrix bonding quality in continuous fiber reinforced specimens, causing cracks and delaminations. Tensile tests consequently revealed a significant effect of the aging on mechanical properties, with a reduction of 17% in ultimate strength for specimens without and 40% for specimens with continuous fiber reinforcement.