P. Tugcu et Kw. Neale, On the implementation of anisotropic yield functions into finite strain problems of sheet metal forming, INT J PLAST, 15(10), 1999, pp. 1021-1040
In this article the implementation of anisotropic yield functions into fini
te element investigations of orthotropic sheets with planar anisotropy is d
iscussed within a plane-stress context. Special attention is focused on the
proper treatment of the orientation of the anisotropic axes during deforma
tion into the finite-strain range. As an example problem the hydrostatic bu
lging of a membrane is considered in conjunction with a recently proposed a
nisotropic yield function. It is shown that the aspects of the plane-stress
assumption, which do not come into consideration in isotropic analyses, ca
n play an important role on the accuracy of the solution when the rotation
of the orthotropic axes enters the computation directly due to the presence
of material anisotropy. When the material anisotropy is considered and whe
n the deformation of the workpiece is not limited to the plane of the undef
ormed sheet (such as cup drawing, hydrostatic bulging, etc.), the numerical
experiments indicate that the only correct formulation is the one based on
numerically imposing the requirement that for the plane-stress application
, the in-plane material axes have to remain in the plane of the sheet durin
g the deformation. (C) 1999 Elsevier Science Ltd. All rights reserved.