Improved structural efficiency in composite manufacturing via hammered printing for large-curvature fiber paths

Maximizing the structural efficiency of composite materials is often limited by the minimum turning radius of fibers in composite manufacturing. Neglected defects, such as local fiber buckling, become more pronounced in regions with a large curvature, leading to reduced load-carrying capabilities and a deviation from the target design specifications. This study introduces "hammered printing" as a novel approach for achieving a large curvature of the fiber path in composite manufacturing. By utilizing the transition of the modulus with temperature of a thermoset epoxy pre-polymer, the proposed hammered printing technique generates a unique pressure effect that improves adhesion between the fiber tow and the substrate. This enables the production of accurate and uniform composite structures with a minimum curvature radius of 2 mm, while reducing the occurrence of wrinkling and bending deformations. A continuous fiber path with a small radius (2 mm) for open-hole plates was accurately printed using this printing pattern. Compared with conventional laminates and drilled composites, the obtained printed samples exhibit 75.3% and 28.8% increments in the tensile and bearing strengths, respectively, indicating that this continuous small-radius fiber path can effectively retain the strength and safety of fastened composite parts. Finally, comparisons indicate the great potential of the proposed technique as a large-curvature-path and high-performance manufacturing alternative for the cutout of composite assemblies in the aerospace and related engineering industries.