Fast joining of aluminum sheets with Glass Fiber Reinforced Polymer (GFRP) by mechanical clinching

The suitability of mechanical clinching (press joining) to join fiber-reinforced plastics with aluminum sheets was investigated. To this end, different types of tools were tested, including split, grooved, flat dies, as well as rectangular ones. The influence of sheet thickness (thin sheets of 2 and 3 mm in thickness) and alloy composition (AA6082-T6 and AA5086) on joinability and mechanical behavior of the joints was analyzed. Single lap shear tests were conducted to characterize the joints, and fracture produced after joining and testing was performed. In addition, the geometry evolution of the joints during clinch joining was studied to understand the material flow and damage evolution of both aluminum and Glass Fiber Reinforced Polymer (GFRP) sheets. The study demonstrates the feasibility of the process, which has great potential for shortening the joining time dramatically as compared to conventional processes (riveting, adhesive bonding). According to the achieved results, round grooved tools are not suitable for this purpose since the formation of GFRP crumbles, which fills the die cavity, thus requiring a long restoration time. On the other hand, the other types of tool enabled joining aluminum with the GFRP sheets successfully. Such joints fractured in the aluminum bulge or in the GFRP sheet by bearing failure; in both the cases, the failure modes developed progressively rather catastrophically. The best performance was achieved by the joints produced by the split die. Such joints were also characterized by limited composite damage in the joint's neighbors, since the damaged composite material was separated from the joint.