Prediction of the mechanical and failure behavior of metal-composite hybrid joints using cohesive surfaces

Friction Spot Joining (FSpJ) is an alternative technique developed to manufacture hybrid lightweight structures by joining metal to composites. This work has developed a finite element model to evaluate the failure behavior of aluminum alloy 2024-T3 and carbon-fiber-reinforced polyphenylene sulfide single spot joints produced by FSpJ. Cohesive surface behavior was applied to model the interface between aluminum and composite in the joint. The different bonding zones of the FSpJ joint were discretized in the model with a specific traction-separation law. The numerical and experimental force versus displacement curves have presented deviations of 8% for the ultimate lap shear force (ULSF) and 1.6% for displacement at failure. The evolution of the damage in the joint occurred preferably from the free edge of the composite due to the differential stiffness between aluminum and the composite. The influence of the edge distance on the mechanical behavior of the joints was also investigated using FEM. It has been observed that longer overlap lengths redistribute the stress in the bonding area more uniformly, thereby delaying the damage evolution in the bonding zones.