Einfluß des Spannungszustandes während des hydraulischen Tiefungsversuchs auf das Umformverhalten von Blechwerkstoffen

摘要

In this thesis a new measuring method for a new method of measuring for the stress strain curve under multi axial stress condition was developed and by means of this special measuring gadget the influence on the forming behaviour und hardening behaviour was investigated. Especially the availability for use of the laser-optics in practice was examined. The laser-optics, consisting of a measuring head with several laser beam apparatuses and a CCD-camera, were used together with an Erichsen-Sheet-Test-Machine for the bulge-test. All functions could be controlled automatically by means of an especially developed Software. The results gained from the laser-optics method prove the independence of the stress strain curve in relation to the orientation of the sample and the measuring drection and the level of the punch velocity. By means of a suitable method of comparing the adequate exactitude of this method could be proven. A fundamental-grundlegend part of this thesis deals with the reproducibility of the laser-optics-method, which was scrutinized in parallel tests with different drawing dies. It turned out that the stress strain curve showed a very good correspondence of the process, whereas the fracture effective strain could not be determined accurately. The possibility of determining the stress strain- and handening curves at very high deformation degree is to be considered as a great advantage of this method compared to the conventional flat tensile test. By using different tools a more realistic material testing under multi axial stress condition can be established as well. Another starting-point was the influence of the stress state on formability and hardening behaviour of the examined steels. Various steels showed various fracture effective strains and deformation ratios using the same drawing dies. While the fracture effective strain decreased significantly during the transition from the pure stretch forming- to the plane strain state, the position of the stress strain curve did not show any influence. Compared with the flat tensile test it became obvious that the stress strain curve of the bulge-test showed a lower position and a more hardening.