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

Paper #:
  • 2017-01-0477

  • 2017-03-28
The use of carbon fiber reinforced polymer (CFRP) composites presents an attractive solution for automotive lightweighting due to the extensive weight savings. One of the key challenges to using CFRP for structural applications is developing and characterizing a robust joining technique for CFRP to metal sheets. Self-piercing rivet (SPR) has emerged as an economical and viable joining technique and is successfully used by the automotive industry in joining aluminum sheets. In this paper, the tensile and fatigue properties of continuous braided fiber CFRP to AA6011-T82 lap-shear SPRs are presented for joints produced with rivet head heights at two values within the nominal range. Even within the narrow range of head heights considered “nominal”, the rivet head piercing was found to have a dominant effect on both the tensile and fatigue properties of the lap-shear SPR joints. Joints created with a flush head height resulted in a greater degree of fiber breakage in the top ply of the CFRP laminate resulting in lower lap-shear strength as compared to SPRs produced with a proud rivet head height. Irrespective of the lap-shear strength, rivet pullout was the most common failure mode observed for both rivet head heights. In fatigue test, the SPRs produced with a proud rivet head exhibited higher fatigue life compared to SPRs produced with a flush rivet head. Interestingly, in fatigue test, the failure mode for both head heights was due to kinked crack growth in the plastically deformed region of the bottom aluminum sheet. The microhardness mapping of the bottom aluminum sheet in the two SPRs indicated lower plastic deformation in SPR produced with a proud rivet head height. In a comparison to AA6011-T82 to AA6011-T82 SPRs, the CFRP to AA6011-T82 SPRs exhibited better fatigue life in lap shear. Overall, the CFRP to AA6011-T82 SPR produced with proud rivet head height exhibited higher fatigue life. An existing structural stress model commonly used for spot welded joints was adapted to generate a master curve to predict the fatigue life of the SPRs.
Also in:
  • SAE International Journal of Materials and Manufacturing - V126-5EJ
  • SAE International Journal of Materials and Manufacturing - V126-5
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