Interfacial performance of phenolic‐sized continuous carbon fiber‐reinforced phenolic resin composites with different impregnation nozzle diameters via 3D printing

Abstract The interfacial bonding strength of the 3D‐printed composites was poor due to the inadequate impregnation. To improve the interfacial performance and mechanical properties of the 3D‐printed composites, carbon fiber (Original‐CF) was modified by oxidation combined with sizing, to obtain Sized‐CF, and continuous carbon fiber‐reinforced phenolic resin (Original‐CF/PF and Sized‐CF/PF) composites were fabricated via in situ‐curing 3D printing. The impregnation nozzle diameter influences the resin content and the impregnation effect of the resin into the fiber bundles. Mechanical properties with different impregnation nozzle diameters of Sized‐CF/PF composites all increased compared to that of Original‐CF/PF composites. The flexural strength of Sized‐CF/PF composites increased by 15.3% and interlaminar shear strength increased by 28.6%, compared to that of Original‐CF/PF composites, when the impregnation nozzle diameter was 0.40 mm. The fiber‐resin interface and the effect of interfacial performance on fracture mode of the composites were investigated systematically. The interfacial performance was improved, owing to the decrease of void defect volume and the increase of impregnation uniformity between the fiber and resin interface; the fracture mode was transferred from longer fiber pulling‐out for Original‐CF/PF composites to shorter fiber pulling‐out for Sized‐CF/PF composites, owing to the improvement of interfacial performance. Highlights Carbon fiber was modified to improve interfacial and mechanical properties. Nozzle diameter of 0.4 mm obtains adequate resin content and extrusion force. Defect volume reduced and impregnation uniformity improved after modification. Flexural strength of the composite increased by 15.3% after CF modification.