Adhesively Bonded Lap Joints : Fracture Mechanisms and Strength Evaluation

Carbon-steel (S 45 C) plates were lap-bonded using a thermosetting-type epoxy, and shear tests were carried out under tensile loading. The stress levels at which interfacial debonding, initiated during testing, occurred were successively detected using the AE (Acoustic Emission) method. Stress singularity fields exist at the two ends of the bonded overlap. Interfacial debonding was initiated in both these ends when the nominal stress reached 60∼70% of the fracture stress. Both the initiation and fracture stresses decreased with an increase in lap length. This was due to the increase in the bending moment at both ends of the bonded overlap. The stress of the interfacial-debonding initiation can be evaluated using stress-singularity K1 and energy release rate G1.