Effect of Double‐Double Lay‐Up on Damage Evolution and Fracture Behavior of Open‐Hole GLARE Laminates Under Tensile Loading

ABSTRACT To clarify the applicability of double‐double (DD) lay‐ups in open‐hole fiber metal laminates (FMLs), this study investigates glass laminate aluminum reinforced epoxy (GLARE) laminates with conventional QUAD lay‐ups and stiffness‐equivalent DD lay‐ups under different 0° fiber contents. The open‐hole tensile response, damage evolution mechanisms, and size effects are systematically examined. The results show that both QUAD and DD laminates exhibit a progressive damage process involving strain concentration around the hole, intralaminar damage initiation, interfacial delamination growth, and final through‐thickness fracture. However, their damage organization mechanisms are markedly different. In QUAD laminates, continuous 0° fiber plies enhance the load‐bearing capacity but intensify the stress concentration around the hole, thereby accelerating matrix damage and delamination in the composite layers and further inducing deflected fracture of the aluminum layers. In contrast, DD lay‐ups promote load redistribution among plies with different orientations, thereby modifying the spatial evolution of matrix and interfacial damage and maintaining a more stable fracture path close to the net‐section direction. As the 0° fiber content decreases, the governing role of fiber fracture in final failure gradually weakens, while matrix damage and delamination become increasingly dominant.