Within the scope of the collaborative research center (SFB) Transregio funded by the German Research Foundation (DFG), damage-controlled forming processes are examined in collaboration with other institutes of RWTH Aachen University as well as with TU Dortmund, BTU Cottbus-Senftenberg and the Max-Planck-Institute for Iron Research to quantify and monitor the influence of forming methods on the properties of workpieces. At WZL, deep drawing is investigated in particular. In addition to tests for the actual deep drawing of round cups, the influence that different processes of the stress states have on the damage is investigated in the material by means of stopped Nakajima tests. Here, different stress states are set using the various geometries of the Nakajima specimens. In contrast to tests for generating forming limit curves, the specimens are removed after a defined die displacement and examined electromicroscopically for their damage state. With the BUP 200 sheet metal testing machine
from ZwickRoell, maximum ram forces of 200 kN and controlled deep drawing speeds up to 1200 mm/min can be achieved. Due to the ability to replace the test tool as well as the tool head quickly and easily, Nakajima tests can be performed with various tool head geometries and thereby the stress states in the sheet metal can be influenced purposefully. The high-resolution measurement of the die displacement allows for precise ending of the test and thereby a return from the damage state to the stress state.