![[ Visit Client Website ]](images/banner.gif)
Although these materials may be resistance spot welded, it has been shown that the fatigue life of spot welded steel joints is often dominated by the geometry and not material strength. This means that resistance spot welded AHSS joints do not exhibit longer fatigue lives than spot welded conventional steels, as would have been expected from the higher base material and joint strengths in these materials.
Self piercing riveting (SPR) is an alternative to resistance spot welding. They have been widely accepted to join aluminum since the mid 1990s and have almost replaced spot welding in this application. As riveting is a “cold” technology, SPR joints will exhibit no HAZ softening so the static strength will be totally dependant on the as-produced base material and rivet strength. As well, SPR joints in aluminum applications have been shown to have very good fatigue resistance. Both of these properties make this technology a potential solutions for the issues faced in steel weldments. However, the high strength and hardness of AHSS make demands on the self piercing rivets, in terms of rivet hardness, cracking issues, joint quality and magnitude of the setting forces. To-date these issues have posed an almost insurmountable problem, to such an extent that the quality of the joints was not satisfactory.
This paper deal with investigations in which, with the help of FEM simulation, the geometries of both rivets and dies were optimised, specifically/especially for applications using the new high strength steels. Tests show that the correlation between the experimental data and the results of the FEM simulation is good. Further, it is shown that the demands on the strength and hardness of the rivet material and the setting forces can be lowered appreciably. Finally, the mechanical properties of the riveted joints can be improved.