3D printing of curved continuous fibre filaments using fused deposition modelling

• Printing error of curved profile is greater for carbon fibres than glass and aramid. • Filament twisting at curved section causes fibre breakage to carbon and glass. • Aramid filament experiences fibre crimping with no fibre breakage. • Damages occurred with twisting include fibre detachment and matrix tearing. • Microstructural damages reduced tensile properties of filaments (largest to carbon) Fused deposition modelling (FDM) is a 3D printing technique capable of fabricating intricately shaped composites through the deposition of continuous fibre filaments. This study investigates the limitations of 3D printing curved filaments using FDM. Polyamide matrix filaments containing continuous carbon, glass, or aramid fibres were 3D printed into curved profiles with different radii as low as 1 mm. A detailed microstructural and mechanical analysis was conducted to assess the damage incurred during curved printing. The deposition mechanism of the FDM process was found to lack high dimensional accuracy when 3D printing continuous fibre filaments in tight curvatures. Issues including filament peeling and twisting resulted in printing error of up to 60 % in the curvature radius, depending on the fibre types. The filaments experienced fibre damage, matrix tearing, and shape distortion during the curved printing process, which subsequently reduced the tensile properties of the printed composites. The average filament strengths were found to be only 30 %, 41 % and 64 % compared to that of the straight printed filament for carbon, glass, and aramid fibre filaments, respectively, when the radius was below 5 mm. These findings provide foundations for identifying optimal FDM printing conditions to produce defect-free composite with complex structures.