EFFECTS OF YIELD SURFACE SHAPE ON SHEET-METAL FORMING SIMULATIONS

Three phenomenological yield criteria are adopted to describe the plas tic behaviour of sheet metals with normal plastic anisotropy. The shee t metals are assumed to be elastic-plastic, rate-sensitive and incompr essible. 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 crit eria with the same value of the plastic anisotropy parameter R on the strain distribution and localization are investigated under a hemisphe rical punch stretching operation and a plane strain drawing operation. The results of the simulations show that the yield surface shape, in addition to the plastic anisotropy parameter R, controls the punch for ce, strain distribution and strain localization for the punch stretchi ng operation. However, the yield surface shape does not affect the pun ch force and the strain distribution significantly for the plane strai n drawing operation. (C) 1998 John Wiley & Sons, Ltd.