Self Pierce Riveting of Materials with Limited Ductility Investigated with the Bai-Wierzbicki Damage Model in GISSMO

The application of joining techniques on advanced lightweight materials with limited ductility, as for example Aluminum or Magnesium die cast, is nowadays a common practice in automotive industry. But in particular during the process of self pierce riveting cracks occur at the closing head of the joint quite frequently. So far it is uncertain, how these cracks influence the mechanical properties of the joint. Advanced damage models like the one of Bai and Wierzbicki [1] have been already used for sheet metal forming. They take into account that the strain at damage depends on the stress state itself. The application of their model to self-pierce riveting of material with limited ductility however involves some challenging tasks. Experimental data for the strain at damage from sheet specimen is only available in a small range from shear to biaxial tension. During the joining process a much higher range of triaxiality occurs, especially at high pressures. For materials with limited ductility the strain at failure is difficult to be measured due to very small localization bands. More problems arise during the simulation. One important is that the element deletion that occurs due to damage leads to zig-zag boundaries. Subsequent contact of these regions yield to convergence problems. So even though the model is very promising, further refinement of the model seems to be essential. The talk will present current results and problems associated with the model. The results also imply modifications of the model approach itself.