Single-lap bonded structures of carbon fiber-reinforced polymer composites are investigated in this study. Two adherend configurations, namely, fabric/fabric (FF) and prepreg/fabric (PF), are selected, and four adhesive layer thicknesses of 0.5, 1.0, 1.5, and 2.0 mm are considered. Tensile–shear tests, digital image correlation (DIC), fracture morphology observation, scanning electron microscopy (SEM), and cohesive zone model (CZM)-based finite element analysis are employed to systematically investigate the effects of adhesive layer thickness and adherend configuration on the mechanical properties, interfacial stress distribution, and damage evolution of the joints. The results show that the shear strength of PF joints is consistently higher than that of FF joints, and the maximum strength of both joint types occurs at an adhesive layer thickness of 0.5 mm. The strength of FF joints decreases monotonically with increasing adhesive layer thickness, whereas the strength of PF joints increases at 2.0 mm compared with that at 1.5 mm. Both joint types exhibit crack initiation at the overlap ends followed by interfacial crack propagation. However, PF joints are mainly characterized by a mixed failure mode involving both interfacial failure and adherend failure, while FF joints transform from adherend failure at smaller adhesive layer thicknesses to mixed failure at larger adhesive layer thicknesses. In addition, different failure modes affect the measured strength of the joints. The finite element results indicate that both interfacial stress and damage preferentially concentrate at the adhesive layer ends. The adhesive layer thickness further affects the crack propagation path and final failure mode by altering the stress level at the overlap ends and the load transfer capacity of the joints.
Yang et al. (Mon,) studied this question.