Effects of yield surface shape on sheet metal forming simulations

Three pheoomenological yield criteria are adopted to describe the plastic behaviour of sheet metals with normal plastic anisotropy. The sheet metals are assumed to be elastic-plastic, rate-sensitive and incompressible. A rate-sensitive thin shell finite element formulation based on the virtual work principle is derived for the three yield criteria. The effects of the yield surface shapes based on the three yield criteria with the same value of die plastic anisotropy parameter A on the strain distribution and localization are investigated under a hemispherical punch stretching operation and a plane strain drawing operation. The results of the simulations show that the yield surface shape, in addition to die plastic anisotropy parameter R, controls the punch force, strain distribution and strain localization for the punch stretching operation. However, the yield surface shape does not affect the punch force and the strain distribution significantly for the plane strain drawing operation. ? 1998 John Wiley & Sons, Ltd.