Forming limit curve determination of a DP-780 steel sheet

C. SCHWINDT; L. IURMAN; M. STOUT; J. W. SIGNORELLI

Congreso; International Congress of Science and Technology of Metallurgy and Materials; 2015

In the present work, the forming limit curve (FLC) of a 1.1 mm thick DP-780 steel sheet is evaluated. The full FLC determinationinvolved tensile tests of planar samples with different notch geometries ? providing data in the tension-compression range ? andNakajima tests with a 40 mm diameter hemispherical punch and different notch geometries, covering the full loading zone of theforming limit diagram. The proposed Nakajima tool geometry reduces the standard test dimensions (ISO 12004-2) by 60%.Results show that the reduced diameter Nakajima test, in the particular case of Dual-Phase steels, overestimates limit strainswhen compared to the tensile test. This observed difference is explained in terms of the presence of a strain gradient through thesheet thickness imposed by the 40 mm diameter Nakajima punch, leading to the conclusion that this reduced sample type is notsuitable for FLC determination when the DP-780 steel sheet is more than a millimeter thick.