Additive manufacturing (AM) facilitates the production of industrial applications with different materials and complex structures. Fused filament fabrication is the most commonly used AM process when considering thermoplastic matrix materials. During this process, filament strands are deposited onto a built-platform layer-by-layer. The layer-wise deposition induces defects and anisotropy in the printed parts. The diffusion depth between adjacent strands significantly influences the resulting mechanical properties. In recent years, FFF is also performed with continuous fibre reinforced filaments. A currently highly researched fibre-matrix combination represents continuous flax fibre reinforced polylactide. This composite is used in this study as the interest in the commercial use of natural fibre-based composites is steadily increasing.
Since components for industrial applications often have to withstand several loading and unloading cycles, the fatigue behaviour of the material needs to be analysed in advance. In order to be able to describe components using numerical methods later on, the material is tested in the direction (UD0) and perpendicular to (UD90) the strands/fibres with tension (R=0.1) and alternating (R=-1) loads. The stress levels are set in a way to reach cycles to failure in the range of 10³ to 106. The loading frequency is selected in order to avoid excessive hysteretic heating. The evaluated fatigue curves for the two loading modes and strand/fibre orientations were compared.