Effect of Planar Anisotropy on the Hole Expansion Ratio of Cold-Rolled DP 590 Steel

Hole expansion ratio (HER) is extensively used in the sheet metal forming industry to assess the sheet metal's stretch-frangibility limit. Cold-rolled dual-phase steel (DP 590) showed planar anisotropy during the uniaxial tensile test. Hill-48 yield criterion was selected to represent the planar anisotropy of DP 590 steel sheet. Material constants i.e. anisotropic yield stress ratios of Hill-48 yield criterion were calculated from the r-values (Lankford coefficient) determined from the uniaxial tensile test. The finite element simulation result showed that the thickness reduction was maximum at 45 degrees to rolling direction during hole expansion, and a crack was visible in the same location during hole expansion experimentation. HER of DP 590 steel and crack location were successfully predicted from the finite element model for Wire-Electrical Discharge Machine cut central hole edge in the present work.