Mechanical characterization of 3D printed composite specimens reinforced with continuous fibres

Over the past few years, additive manufacturing has evolved from a rapid prototyping technology into a manufacturing process increasingly used to produce functional end-use parts. However, the mechanical performance of additively manufactured composites remains highly dependent on process parameters, leading to significant variability in their properties. This study investigates the tensile behaviour of continuous glass fibre-reinforced Onyx FR composites manufactured using a Markforged X7 printer. A design of experiments was employed to evaluate the combined influence of fibre orientation, fibre-block distribution and process-induced porosity on tensile behaviour. Tensile tests were performed to measure Young’s modulus and ultimate tensile strength, while X-ray computed tomography was used to quantify porosity and determine the effective load-bearing cross-section. The results identify fibre orientation as the dominant parameter governing tensile behaviour of the printed composites. For the same volume fraction, the mechanical properties strongly depend on their distribution through the specimen thickness. Concentric configurations exhibited Young’s modulus values approximately twice those of isotropic configurations for the same number of reinforcement blocks and infill density. These findings demonstrate that optimizing the distribution and orientation of continuous fibre reinforcement is more effective than increasing the number of reinforcement blocks to improve tensile performance.