Impact of Rivet Head Height on the Tensile and Fatigue Properties of Lap Shear Self-Pierced Riveted CFRP to Aluminum

Tensile and fatigue properties of continuous braided carbon fiber reinforced polymer (CFRP) composite to AA6111 self-piercing riveted (SPR) lap shear joints are presented. Rivets were inserted at two target head heights separated by 0.3 mm. Even within the narrow range of head heights considered, the flushness of the rivet head was found to have a dominant effect on both the monotonic and fatigue properties of the lap shear SPR joints. Joints created with a flush head resulted in a greater degree of fiber breakage in the top ply of the CFRP laminate, which resulted in lower lap shear failure load as compared to SPR joints produced with a proud rivet head. Irrespective of the lap shear failure load, rivet pullout was the most common failure mode observed for both rivet head heights. In fatigue tests, the SPR joints produced with a proud head exhibited higher fatigue life compared to SPR joints produced with a flush head. Joints produced with a proud head resulted in slightly longer fatigue life. However, the failure mode in fatigue tests for both head heights was due to crack growth in the plastically deformed region of the bottom aluminum sheet. Microhardness maps of the bottom aluminum sheet showed a lesser degree of plastic deformation in joints produced with a proud head height. A structural stress model commonly used for spot welded joints was adapted to generate a master curve to predict the fatigue life of the SPR joints.