Influence of 3D printing path and continuous Flax yarn reinforcement on the performance of additively manufactured T-joints for large-scale components

The design of optimized 3D printing paths is a key factor in improving the structural performance of continuous fiber-reinforced composites, especially for complex geometries are difficult to achieve using conventional manufacturing techniques. This study investigates the combined influence of continuous flax yarns as a bio-based reinforcement for Polylactic Acid and layer-wise printing path strategies on the mechanical response of printed components. Special emphasis is placed on T-joint configurations, which represent critical structural regions subjected to complex multi-axial stress states and govern load transfer and failure mechanism. Printing paths were specifically engineered to follow load-transfer directions, and intermediate reinforcement layers were introduced to enhance joint behavior. Experimental results demonstrate that both path optimization and continuous natural fiber reinforcement significantly improve the rotational response of the joints, leading to increased stiffness and moment capacity, as well as reduced brittleness and improved ductility when compared to unreinforced specimens. The results further indicate a synergistic interaction between adaptive path design and bio-based continuous yarn reinforcement, offering a viable route toward high-performance and sustainable continuous fiber-reinforced thermoplastic composites capable of sustaining complex loading conditions. In addition, a simplified bilinear model is proposed to describe the moment–rotation behavior of T-joint profiles, supporting structural interpretation and facilitating future numerical and design-oriented applications.