Ply Scale Modeling and Fatigue Behavior of Glass/Carbon Epoxy Hybrid Composites

Hybrid composites facilitate innovative material design by incorporating high-stiffness, robust carbon fibers with economical glass fibers within a resin matrix. This combination allows for tailored mechanical properties suited to specific requirements, particularly when directional loading properties are critical. This study employs the Tsai–Wu failure criterion to determine the optimal stacking sequence for a hybrid composite shaft with high-stiffness carbon fibers on the surface and cost-effective glass fibers in intermediate layers under combined torsional and bending stresses. On the basis of the failure analysis, test samples were prepared with epoxy resin, E-glass fibers (nonhybrid), or a combination of carbon and E-glass fibers (hybrid) for fatigue testing on a custom-designed fatigue machine. The fatigue test results demonstrated that the hybrid composites exhibited greater fatigue strength when high-stiffness carbon fibers were placed on the outer surface, where the bending stress is maximum. The S-N curves for both composites showed a consistent decrease in fatigue strength as the stress level increased, with no clear endurance limit.