Interfacial performance and fracture patterns of 3D printed continuous carbon fiber with sizing reinforced PA6 composites

A sizing procedure was utilized in 3D printing of continuous fiber reinforced thermoplastic composites (CFRTPCs) process to improve their interfacial performance. The sized carbon fiber (SCF) reinforced PA6 (SCF/PA6) was successfully printed, exhibiting 42.2% higher interlaminar shear strength (ILSS) than that of virgin carbon fiber (VCF) reinforced PA6 (VCF/PA6). The influence of sizing and printing process on interfacial performance and fracture patterns was studied systematically. Weak interfacial performance with large fiber pull-out was observed in VCF/PA6. Strong interfacial performance with fiber cut-off arose in SCF/PA6 under excessive forming pressure. They were both detrimental to mechanical properties. Moderate interfacial performance with finite fiber pull-out in SCF/PA6 under decent forming pressure achieved maximum 82% and 246% increasement in flexural strength and modulus respectively. The interface optimization strategy for 3D printed CFRTPCs was set up, which could speed up the technological progress for practical industrial applications.