Localized necking in thin metal sheets is analyzed by using the M-K-model a
pproach, and the effect of a number of different non-proportional strain pa
ths prior to the occurrence flow localization are considered. The analyses
account for plastic anisotropy, using four different anisotropic plasticity
models to fit a set of experimental data for cold-rolled steel sheet. The
predicted forming limit diagrams show strong dependence on whether or not t
he load on the sheet is removed between two load steps on a non-proportiona
l strain path. This dependence is investigated in detail for one of the ani
sotropic plasticity models, and it is shown that elastic straining plays a
large role, as the stresses quickly move from one point of the yield surfac
e to another. When the load is removed between steps, the stress point move
s in a different manner, which results in quite different flow localization
response. (C) 2000 Elsevier Science Ltd. All rights reserved.