Fibre flow and void formation in 3D printing of short-fibre reinforced thermoplastic composites: An experimental benchmark exercise

This paper for the first time presents experimental results for fibre flow and void formation during 3D printing of short fibre reinforced thermoplastic composites by fused filament fabrication (FFF). Short carbon fibre T300 reinforced nylon-6 composite is selected as the printing material. X-ray micro-tomography (µCT) scans are performed on the raw filament, in-nozzle melted filament, extruded printing bead and on-bed printing bead to trace the through-process evolution of fibres and voids for the specific nozzle used therein. Qualitative visualisation of voids fraction and fibre orientation, length and fraction, as well as quantitative analysis are carried out using image processing techniques. The results show that the orientation and volume fraction of fibres vary with different internal geometry of the nozzle and fibre misalignment occurs in the on-bed printing bead because the relative motion between the nozzle and the print bed disturbs the flow field. Also the fibre length decreases slightly during the printing process due to the collision between fibre and nozzle wall when the melted materials pass the nozzle. For the void volume fraction, most voids are generated when the melted filament is extruded from the nozzle, and porosity decreases in the on-bed printing bead. The reported experimental data of through-process evolution of fibre flow and void formation can also be used for benchmarking and/or validating computational models for 3D printing of short fibre reinforced polymer composites.