# Self-Piercing Riveted Joint of Vibration-Damping Steel and Aluminum Alloy
## 3 Results and Discussion
### SPR Joint of Aluminum Alloy (Top) and Vibration-Damping Steel (Bottom)  
Figure 10 shows the cross-sectional views of SPR joints of aluminum alloy (top) to vibration-damping steel (bottom) formed with different die types, as presented in Figure 3. Different  
Figure 8: Tensile–shear loads for SPR joint of vibration-damping steel (top) and Al5052-H32 (bottom) with respect to SPR die type. Figure 9: Failure modes for SPR joint of vibration-damping steel (top) and Al5052-H32 (bottom) with respect to SPR die type. (**a**) Type A1 die, (**b**) type A2 die, (**c**) type A3 die, (**d**) type B die, and (**e**) type C die. from the reversed sheet material's stack configuration, the rivet shank in these SPR joints were fully filled with the stack materials, so no rivet cavity was formed, which is commonly reported when a ductile metal such as aluminum alloy is used as the top material [19; 24; 25]. The rivet penetrated through the top sheet of the bottom vibration-damping steel, but not into the bottom sheet of the vibration-damping steel. Hence, the top steel sheet of the vibration-damping steel actually sustained the mechanical interlocking for the joint as the bottom sheet. The bottom steel sheet of the vibration-damping steel increased the mechanical performance of the top steel sheet and made a bottom sealing. The two outer sheets of the vibration-damping steel were stuck to each other by the adhesive layer. The rivet head gap was hardly observed compared with the reversed stack configuration, regardless of die type. Figure 11 shows the measured geometrical indices of the SPR joints for this material stack with respect to the SPR die type. The results show that the stack of aluminum alloy (top) to vibration-damping steel (bottom) had more interlock width than the reverse stack for all types of dies. The rivet shank cavity was fully filled with the stack material and the rivet head gap was tightly sealed because the top sheet aluminum alloy had a better formability than the top vibration-damping steel sheet for the reversed stack. As a result, more rivet shank penetrated into the bottom sheet, and thus less shank was entrapped by the top sheet. The type A1 die gave the largest interlock width, and the smallest interlock width was obtained with the type B die. The interlock widths of other joints were similar to each other, as shown in the figure. It was also observed, as is the case for the reverse material stack, that for dies with a flat-bottom shape (types A1, A2, and A3), the increase of the die taper angle, as well as die diameter, reduced the interlock, since the number of constraints on the bottom sheet reduced with increasing die cavity. The bottom thickness had a contrary trend with the interlock width for dies with a flat-bottom shape (types A1, A2, and A3); however, a clear trend of the bottom thickness was not found for the non-flat die (types B and C), whose trend was also observed in the case of the reverse material stack configuration. Figure 10: Cross-sectional images of SPR joints of Al5052-H32 (top) and vibration-damping steel (bottom) with respect to SPR die type. (**a**) Type A1 die, (**b**) type A2 die, (**c**) type A3 die, (**d**) type B die, and (**e**) type C die. The tensile-shear test results for the SPR joints of aluminum alloy (top) and vibration-damping steel (bottom) are presented in Figure 12. The results show that this material stack configuration had a greater tensile shear load than the reversed stack for all types of die. This is attributable to the overall increase of the interlock width when the vibration-damping steel was used as a bottom sheet.