Quantifying Fiber Bridging in Mode I Fatigue Delamination of CFRP/GFRP Hybrid Laminates Using a Superposed Traction–Separation Model

Hybrid CFRP/GFRP laminates offer an attractive balance between mechanical performance, damage tolerance, and cost efficiency. However, fiber bridging during mode I delamination increases crack-growth resistance while masking the intrinsic fatigue behavior of the material. This study applies a traction–separation-based superposition approach to quantify and isolate the contribution of fiber bridging in unidirectional hybrid laminates under mode I fatigue delamination. The methodology separates monotonic (during pre-cracking) and cyclic bridging contributions using bridging traction curves and fatigue crack-growth data, enabling reconstruction of the zero-bridging Paris curve. Hybrid laminates exhibited enhanced fracture toughness and fatigue resistance, while maintaining intermediate bridging traction behavior compared to nonhybrid systems. After removing bridging effects, hybrid laminates still showed superior intrinsic fatigue performance, indicating that hybridization contributes through mechanisms beyond extrinsic toughening alone. The proposed methodology provides an experimentally efficient framework for fatigue characterization of advanced composite laminates affected by fiber bridging.