Fibre misalignment and breakage in 3D printing of continuous carbon fibre reinforced thermoplastic composites

This paper investigates the formation of manufacturing induced fibre misalignment and breakage during fused filament fabrication (FFF) 3D printing of 1 K continuous carbon fibre filament. Single stripes at various turning angles and curvatures are printed by a desktop printer Prusa i3 using a specific brass nozzle and characterised using X-ray computed micro-tomography (µCT) and optical microscopy. A finite element (FE) model of the printing process is also established to support the experimental measurement. It has been found that high porosity and fibre misalignment in the printed straight stripe result from the weak fibre/matrix interface and the uneven pressure executed by the nozzle. Increase of turning angle and/or reducing of curvature radius leads to more aggravated printing defects, including shape inaccuracy, fibre twisting, folding and misalignment, due to the excessive force from the nozzle, debonding with the print bed and the unmatched geometry of nozzle outlet and fibre filament. Severe fibre breakage and significant change of thickness can be seen in the samples with turning angles larger than 120° or curvature radius smaller than 5 mm, while the wrinkles of the stripe in the inner periphery appear more frequently as the curvature radius decreases.