On the influence of glass fiber mat on the mixed-mode fracture of composite-to-metal bonded joints

In this work, the influence of a layer of glass fiber mat (GFM) inserted in a bi-material bonded joint interface is investigated as a toughening mechanism to improve the fracture performance of bonded structures. Composite-to-metal bonded specimens were manufactured by hand lay-up using two different consolidation processes: at room pressure or using vacuum bagging. The fracture behavior was evaluated under quasi-static loadings using the mixed-mode bending (MMB) test. Test results revealed an increase of the fracture toughness with the insertion of an adjacent layer of GFM. The toughening mechanism is associated with a more irregular fracture surface profile. It was verified a relationship between the fracture surface roughness and the fracture toughness. The toughening effect showed to be more evident in higher mode II fracture conditions. The insertion of a layer of GFM and the use of vacuum pressure in the consolidation of the composite increase the fracture performance of composite repairs in metal structures.