Post-necking behaviour modelled by a gradient dependent plasticity theory

The delay of the onset of localization and the post-necking behaviour for stretched thin sheets are determined by three-dimensional effects, Thus, a 2-D finite element analysis based on a local plasticity theory will give a physically unrealistic mesh dependent solution. This, in spite of the fact that the stress state, is essentially two-dimensional. By incorporating a length scale with relation to the thickness of the sheet, it is demonstrated how a 2-D finite element analysis based on a gradient dependent plasticity theory can give a good approximation of the post-necking behaviour. This is illustrated by numerical comparison of results from a full 3-D finite element analysis, with results from a 2-D finite element model based on a finite strain version of a gradient dependent Jzflow theory. Some numerical problems in the modeling will be discussed briefly. 0 1997 Elsevier Science Ltd.