Research on joint strength and energy absorption of CFRP and Al sheets bonded-FDS hybrid joining

The application of a composite-metal alloy lightweight body structure is one of the ways to achieve lightweight in an automobile. Materials such as carbon fiber reinforced polymer (CFRP) and aluminum alloys are widely used in the automotive industry due to their excellent performance. However, the significant differences in performance parameters between CFRP and aluminum alloy materials make joining heterogeneous materials challenging. Therefore, a rational joining process is crucial for the development of CFRP–aluminum alloy structures. This study proposes a hybrid joining method that combines flow drill screw (FDS) and adhesive bonding to join commonly used aluminum alloy sheets with CFRP sheets in automotive body manufacturing. Finite element analysis simulations were used to compare and characterize the failure modes of the bonded-FDS hybrid joints in tensile tests. The results were verified for accuracy. Tensile tests were conducted to compare the mechanical performance and failure modes of bonded joints, FDS joints, and hybrid joints. By analyzing the load–displacement curve, it was found that the FDS process in the hybrid joining damages the internal structure of the adhesive layer. However, the joint strength is still higher than that of the single joint strength, and the energy absorption value is about 4.7 times that of the adhesive and 1.6 times that of the FDS. This study provides a new industrial solution and serves as a reference for failure performance in composite material structures in the automotive industry, especially in cases involving one-sided access joining points.