Experimental investigation and numerical modelling of sheet metalformability

Abstract

In the present work the formability of the steel Docol 600DL has been investigated. The main objectives were 1) to execute and interpret an experimental formability test program on a dual-phase high-strength steel(Docol 600DL), and 2) to evaluate a particular constitutive and fracture model for its ability to represent the experimental results.

The formability tests executed were the Marciniak-Kuczynski test and the Nakajima tests. Simulations ofboth tests were performed in the explicit FE-code LS-DYNA. Forming Limit Diagrams (FLDs) were found from both experiments and from the numerical analysis of the experiments, in addition an analytical FLD wasfound. FLDs from the different methods and from experiments and analyses were compared.

The analytical FLD from the FLD-calculator seems to give a strain path that coincides well compared with the M-K test. Compared to the Nakajima experiments, the analytical FLD shows a bit more conservative behavior than the test, especially at equibiaxial strain. For the area between plane strain and equibiaxial strain, the FLC for the Nakajima and M-K tests are quite similar. The limit strains established from analyses of the tests had a better agreement with the experiments for the Marciniak-Kuczynski tests than for the Nakajima tests.

Localized necking was shown to be the failure mode for the material close to plane strain, while material subjected to equibiaxial stretching was found to fail through fracture.