Tailoring the Flexural Performance of Additively Manufactured Carbon/Glass Fiber Hybrid Composites: Synergistic Optimization of Hybrid Ratio and Ply Stacking Sequence

ABSTRACT The growing demand for lightweight, high‐performance composites in rail transit applications has driven the development of hybrid fiber‐reinforced materials with tunable flexural properties. This study investigated the synergistic effects of hybrid ratio and ply stacking sequence on the flexural performance of additively manufactured carbon/glass fiber‐reinforced polyamide‐6 composites. Eight laminate configurations were fabricated via multi‐material fused deposition modeling (FDM), with carbon fiber volume fractions ranging from 0 to 100 vol% and stacking architectures classified as symmetric, sandwich, or alternating. Quasi‐static three‐point bending tests were performed in accordance with ASTM D7264, with deformation fields captured by digital image correlation (DIC) and fracture mechanisms analyzed using scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM). The results indicated that flexural strength and modulus exhibited a nonlinear decline with decreasing carbon fiber content, identifying a critical threshold at approximately 25 vol%, below which both properties deteriorated sharply (up to a 56.6% reduction in modulus), whereas increasing glass fiber content enhanced failure strain. At a 1:1 carbon/glass fiber ratio, carbon‐outer configurations (e.g., C4G8C4) achieved superior strength (233.40 MPa) and modulus (19.96 GPa), whereas glass‐outer designs (e.g., G4C8G4) enhanced failure strain by 87.5% (4.05%) through ductile damage. Alternating sequences (G2C2) achieved a balance of strength (182.08 MPa) and damage tolerance via progressive failure. These findings demonstrate that hybrid ratio governs strength‐toughness trade‐offs, while stacking sequence dictates failure modes, providing a framework for optimizing additively manufactured hybrid composites for structural applications.