A 2-D non-local analysis of hydroforming for thin sheets

An enhanced membrane theory is used to analyse hydroforming of thin metal s heets. The use of a plane stress or membrane model for such metal forming s tudies, rather than a full three dimensional numerical analysis, is highly advantageous from the point of view of reducing computer requirements, but the onset and development of localized plastic straining is not realistical ly predicted. It has been found that a nonlocal formulation of a membrane m odel, in which a material length is used to represent thickness effects, ca n give rather accurate predictions of the full 3-D effects. The non-local m odel implemented here in a hydroforming study is a 2-D version of gradient dependent plasticity theory. The model is used to illustrate the effect of different initial geometries and of different material length parameters.