Bending effects on flow localization in metallic sheets

Abstract

In the present work the dependence of critical strain on thickness in finitely stretched metallic sheets is investigated. A finite strain axisymmetric shell theory is developed for the modelling of the punch stretching of a thick circular plate and a consistent onset of localization criterion for the shell is proposed. Experimental results as well as numerical calcutions, in the case of mild steel plates deforming under the action of a frictionless hemispherical punch, show that if the onset of strain localization is used as the failure criterion, the material’s thickness has very little influence for plate thicknesses usually used in sheet forming. The opposite held viewpoint in the literature that the sheet thickness significantly affects the critical strain is due to the experimental use of the fracture strain as the failure strain.