Abstract
<title>Abstract</title> <p>The design flexibility enabled by 3D printing is opening new opportunities for composite structures beyond the limitations of conventional manufacturing. Here, a dual-state printing strategy is presented to maximize mechanical performance in additive-manufactured short fiber-reinforced composite structures. By coupling Finite Element Analysis with smart infill-pattern planning, the dual-state technique takes principal-stress-driven toolpath generation to the next level, with customizable adjustments to fiber anisotropy for composite applications. This hybrid printing method increases both the failure load and energy absorption by strategically creating aligned and random fiber-orientation areas within the same model. To establish the theoretical foundation, the performance enhancement of the dual-state printing methodology is first numerically investigated. Thereafter, carbon fiber-reinforced thermoset composite samples with various sizes and shapes were manufactured using Direct Ink Writing 3D printing. The 3D-printed geometries were then tested under different boundary conditions to demonstrate the capabilities of the presented dual-state printing methodology in practice. Relative to single-state and conventional infill strategies, dual-state printed specimens exhibit simultaneous increases of up to ~20% in failure load and up to ~17% in energy absorption across bending and tensile tests, achieving the strongest and most damage-prolonged response among all architectures.</p>