Fused Filament Fabrication is a very common additive manufacturing technology and several manufacturers have developed commercial 3D-printers that enable the use of fibre-reinforced filaments in order to improve the mechanical properties of the printed parts. The obtained material is a composite that exhibits complex mechanical properties. The aim of this study is to characterize the mechanical behaviour of 3D-printed continuous glass fibre-reinforced polyamide composites. In a first step, we focus on the reinforced filament: the heterogeneity of its microstructure is evidenced as well as its brittle elastic tensile behaviour. In a second step, parts of different fibre orientations and fibre volume contents are manufactured using a Mark Two 3D-printer (MarkForged®), their microstructure is analysed and tensile, flexural and short beam bending tests are performed. As expected, the results show a significant influence of fibre volume content and fibre orientation. Standard homogenization methods are used to compare the predicted mechanical behaviour to the experimental results. Regarding the elastic stiffness, a good correlation is observed when the material is loaded in the direction of the fibres. Regarding the tensile strength, the results show that no benefit is obtained above a fibre volume content of about 11%. These results highlight the importance of choosing an optimised stacking sequence prior to the printing process, in order to obtain composites with the desired mechanical properties. The mechanical results are analysed in the light of Scanning Electron Microscopy observations of specimen cross-sections before and after testing.
