Numerical simulation of tensile tests of prestrained sheets

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 yield criterion with isotropic hardening describes the anisotropic plastic properties of the sheet. The isotropic hardening is modelled by a modified Swift law that describes the response of prestrained materials in reloading. Two different situations were simulated: reloading in tension of samples with constant cross sectional area and reloading in tension of samples with two zones of slightly different cross sectional areas. The results show that the strain distribution along the tensile axis of a prestrained sample depends on the level of the prestrain and also on the presence and size of geometrical fluctuations in the cross section, which always occur in experimental samples. This dependence is higher for materials with lower work-hardening rates.