# Self-Piercing Riveted Joint of Vibration-Damping Steel and Aluminum Alloy
## 3 Results and Discussion  
### SPR Joint between Vibration-Damping Steel (Top) and Aluminum Alloy (Bottom)  
Figure 6 shows the cross-sectional views of the SPR joints of vibration-damping steel (top) to aluminum alloy (bottom) formed with different dies, as presented in Figure 3. While the cavity inside the rivet shank (or rivet cavity) was formed for the dies with a flat-bottomed cavity (types A1, A2, and A3), the rivet cavity was significantly reduced when non-flat dies (type B and C) were used due to the protruded part of the dies. The punched slug from the top vibration-damping steel embedded into the shank cavity separated in common. On the other hand, the top sheets of the joints barely separated, showing a little slipping between the outer steel sheets of top vibration-damping steel. Figure 4: Definition of geometrical indices of the SPR joint. Figure 5: Schematic diagram of tensile–shear test specimen (KS B ISO 14273). The rivet head gap between the rivet head edge and the upper surface of the bended top sheet in the joint represents the amount of top surface sealing. The gap increased with the increase of the die taper angle and diameter, because the die-to-rivet volume ratio (R) increased as the die taper and diameter increased, as presented in Figure 3. As described by [PERSON] et al. [19], for R \(>\) 1, the die with the larger cavity imposed fewer constraints on the material stacks, and thus the bending curvature of the top sheet increased with increasing R and resulted in the gap increase. In the case of the not-flat dies (type B and C), the projection (or tip) of the dies did not reduce the gap. Especially for the type C die, its R was less than that of type A1 die but the gap was more than that of the type A1 die. Hence, the tip of the not-flat die was not effective for top surface sealing, but only for reducing the rivet cavity. Figure 7 shows the measurement results of geometrical indices for the SPR joint of the vibration-damping steel (top) and Al5052-H32 (bottom) with respect to the SPR die type. As seen in the figure, the joint made from the type A1 die has the largest interlock width, and it decreases in the order of type A2, type A3, type B, and type C. The flat dies (types A1, A2, and A3) induced a larger interlock width compared with the non-flat dies (types B and C). For the flat dies, the interlock width was not only reduced by the increase of the die taper angle, but also the increase of the die diameter. The increase in both the die taper angle and die diameter contributed to the increase of the die volume in the radial direction. Consequently, the bottom sheet (Al5052-H32) was more deformed in the radial direction, leading to less interlocking between the rivet shank and lower sheet. The bottom thickness of the joints was much larger than the interlock width of the joints, due to the small penetration made by the rivet shank in the bottom sheet. For the flat die, the bottom thickness of the joints had an opposite trend with the interlock width; however, no distinct trend was observed when the bottom thickness of the non-flat die was compared with that of the flat die. Figure 6: Cross-sectional images 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. Figure 7: Geometrical indices for SPR joint of vibration-damping steel (top) and Al5052-H32 (bottom) with respect to SPR die type. The tensile-shear load of the specimens is shown in Figure 8. The joint made from the type A1 die had the highest tensile-shear load, owing to the large interlock width, and it decreased with the decrease of the interlock width (refer to Figures 7 and 8).