Influence of Deposition Strategy and Fiber Alignment on the Mechanical Anisotropy of Short-Fiber-Reinforced Polyamide Manufactured by Additive Manufacturing Material Extrusion

Short-fiber-reinforced composites (SFRCs) are widely used for their high strength-to-weight ratio. In the Additive Manufacturing (AM) field, Material Extrusion (MEX) processes inherently induce anisotropy, primarily due to fiber alignment along the deposition path, making printing direction and layer orientation critical for mechanical performance. In this study, specimens made of Onyx®, a carbon short-fiber-reinforced polyamide, were fabricated by varying their orientation on the build platform, thereby producing different infill deposition directions. Each replica contained 25 layers. Two deposition strategies were investigated: a conventional alternating ±45° raster pattern and a 0°/90° configuration. Owing to the odd number of deposited layers, the latter resulted in two distinct stacking configurations, namely 0°/90° and 90°/0°, depending on the orientation of the first deposited layer. With such a strategy, it was possible to obtain configurations with a predominance of fibers either aligned with or transverse to the loading direction, depending on the orientation of the first-deposited layer. Mechanical test results were systematically compared to evaluate the influence of deposition strategy and fiber orientation on tensile performances. The effect of extrusion on fiber alignment was evaluated using Scanning Electron Microscopy (SEM). Mechanical behavior was evaluated using replicated tensile testing (five specimens per condition) and SEM-based fiber-orientation analysis. The investigation confirms the anisotropic nature of MEX-produced SFRCs. In particular, the 0°/90° configuration showed reductions of approximately 24% in tensile strength and 58% in elongation at break compared with the ±45° configuration. These results demonstrate that both extrusion-induced fiber orientation and layer-wise deposition strategy play a crucial role in defining the mechanical response of the material.