Failure analysis of composite-to-titanium single lap adhesive joints subjected to tensile loading

Similar (composite, titanium) and dissimilar (composite-to-titanium) single lap adhesive joints were made of the titanium alloy and aramid fiber composite. The joint surface strain and failure modes under tensile load were characterized using a digital image correlation (DIC) system, strain acquisition system and optical microscope (OM). The strain distribution and failure morphology of similar and dissimilar joints were compared to analyzing joints' bonding performance and failure characteristics. The strain evolution in the dissimilar joint was quantified to figure out failure process. The results showed that the lateral offset and deformation of dissimilar joints are higher than those of titanium and composite joints, which causes dissimilar joints to have lower bonding strength. Shearing and peeling stress concentrate at the upper end of composite, and the joint firstly fails from here. After starting failure, a high tensile strain region appears on the composite surface, and a high bending strain region appears on the surface of titanium. Both regions move along the debonding direction. Tensile and bending stress of adherend at the edge of remaining bonded area further rise, resulting in eventual failure of the joint. The joint appears in sequence with the failure of composite delamination and the interfacial failure between the titanium and adhesive.