Effects of hygrothermal aging on the tensile and bonding performance of consolidated 3D printed polyamide-6 composites reinforced with short and multidirectional continuous carbon fibers

In this research work, the effectiveness of hot pressing in improving the durability of 3D-printed thermoplastic composites subjected to cyclic hygrothermal aging is experimentally demonstrated. By varying the type (short or continuous) and orientation (unidirectional or multidirectional) of reinforcement fibers, different material configurations were tensile tested before and after aging. Moisture absorption of pressed composites was evaluated during aging time against unpressed reference samples, and correlated to the characteristic volume fractions of matrix, fibers, and voids. The pressed composites were then used as substrates of structural epoxy-adhesive joints, whose shear strength and relative decay during aging were evaluated by varying the overlap length between laminates. Supported by fracture analysis, the experimental results showed that post-printing consolidation is beneficial to both the short-term and long-term performance of 3D-printed composites, as it leads to a reduction in the void volume fraction that partially counteracts moisture absorption by the hygroscopic polyamide matrix.