Effect of Hole‐Shape on Tension‐Tension Fatigue Life and Damage Mechanisms of Open‐Hole 3D Woven Composites

Open‐hole three‐dimensional woven composites (3DWC) are increasingly used in cyclically loaded structures, yet the role of hole‐boundary geometry in their fatigue damage evolution remains insufficiently understood. This study combines tension–tension fatigue experiments with mesoscopic progressive damage simulations to examine seven central‐hole geometries with a characteristic size of 6 mm. Circular, square, and rhombic holes were investigated experimentally, and the model evaluated against these tests was subsequently applied to waist‐shaped, slit, hexagonal, and octagonal holes as numerical parametric cases. For the experimentally tested configurations, the predicted fatigue lives reasonably reproduced the measured life ranges, with most results falling within a twofold error band; the predicted damage‐localization regions were also qualitatively consistent with the observed final fracture morphologies. The numerical analyses further indicate that transverse yarn damage constitutes the dominant damage mode and that boundary continuity, corner distribution, and corner orientation relative to the yarn system jointly control stress redistribution and fatigue damage paths. Smooth‐boundary holes promote dispersed damage accumulation and slower stiffness degradation, corner‐symmetric holes guide damage along preferred directions, and corner‐dispersed holes induce multisite localized damage. These findings link hole‐boundary features to fatigue failure mechanisms in open‐hole 3DWC and provide a basis for designing noncircular cut‐outs.