Microscale Damage Evolution and Failure Behavior of Metal–Composite Friction Spot Joints: Modelling and Experimental Analyses

This study aimed to understand the damage evolution at the interface of AA2024-T3/CF-PPS friction spot joints. For this purpose, the finite element method was applied and the bonding zones of the joints were discretized based on a traction–separation law. It was observed that the damage had initiated at the AZ (adhesion zone) and then propagated as a symmetric linear front from the edges towards the center of the joined area. Nevertheless, as the damage advanced inside the PDZ (plastically deformed zone), its propagation became an asymmetrical linear front that evolved preferably from the free edge of the composite part due to the higher peeling stresses in this region (asymmetrical secondary bending of the structure). Based on the findings of this study, modifications are proposed to the failure theory previously stated for friction spot joints.