Morphology and fracture properties of pure and reinforced aluminum‐epoxy adhesive joints

Several types of nonreinforced and reinforced epoxy‐aluminum adhesive joints were prepared and investigated. High modulus carbon fibers and hollow glass microspheres were used as reinforcement. The amount of curing agent, postcure time, adhesive thickness, and type and amount of reinforcement were varied throughout this study, and their effect on fracture energy was determined. Unstable crack propagation through the adhesive layer was observed. Nodular morphology typified all fracture surfaces of nonreinforced adhesive joints, indicating the existence of an inhomogeneous thermosetting network. Electron microscopic evidence was obtained for plastic flow in crack initiation and crack arrest regions. The nature of this plastic flow was discussed in terms of changes in the resin morphology.