The effect of cross section Variation on formability of prestrained samples
has been investigated using finite element simulations of a standard sheet
tensile test. The mechanical model takes into account large elastoplastic
strains and rotations that occur during deformation. Hill's orthotropic yie
ld criterion with isotropic hardening describes the anisotropic plastic pro
perties of the sheet. The isotropic hardening is modelled by a modified Swi
ft law that describes the response of prestrained materials in reloading. T
wo different situations were simulated: reloading in tension of samples wit
h constant cross sectional area and reloading in tension of samples with tw
o zones of slightly different cross sectional areas. The results show that
the strain distribution along the tensile axis of a prestrained sample depe
nds on the level of the prestrain and also on the presence and size of geom
etrical fluctuations in the cross section, which always occur in experiment
al samples. This dependence is higher for materials with lower work-hardeni
ng rates. (C) 1999 Elsevier Science S.A. All rights reserved.