Investigation on anisotropic toughness and cracking behavior of woven lay-up Fiber Metal Laminates with two-level customized interfaces

Interlaminar toughening for metal-polymer interfaces in woven lay-up Fiber Metal Laminates (w-FMLs) is a critical concern, demanding isotropic mechanics and higher energy dissipation. Customizing interfaces with interlocking structures like dimples or grooves has proven effective in meeting these requirements, while the resulting two-level features introduce greater complexity in toughening effects, and interfacial mechanics are influenced by factors such as fiber orientation and resin distribution. To understand the anisotropy effect and toughening mechanics induced by different two-level features, three types of two-level customized interfaces of w-FMLs are examined. Edge shear tests are utilized to evaluate interfacial mechanics and toughness, with a focus on tracing crack propagation behaviors. Through numerical simulation and characterization, the toughening effect and its mechanisms are unveiled, revealing that differences in toughness pinning effect and local plastic deformation of the customized interfaces are the primary determinants of interlaminar toughness. Additionally, a coupling effect between the woven core and interfaces is observed, showing that the superposition of the tougher orientation of the woven core on the strong toughness pinning orientation of the interfaces is a crucial factor in determining excellent overall interlaminar toughness.