1. Introduction

Most of Code_Aster’s behavior laws can be used under the hypothesis of small disturbances (HPP), which allows the initial and current geometric configurations to be confused. However, when the deformations become significant (the limit is generally set at 5%), this hypothesis is no longer verified. The notions of particle and partial derivatives are then different, and as a result the laws of behavior formulated incrementally lose their objective character (independence of the mechanical state as a function of the observer); an annoying consequence is the possible evolution of the constraints for a rigid body movement, contrary to physics.

In order to regain objectivity, which is therefore essential to guarantee a good reliability of the result, a large distortion strategy is possible. The purpose of this document is to present the formalism implemented in Code_Aster to deal with isotropic and kinematic cold-working behavior laws and the Von Mises criterion.

We present formalism GDEF_LOG, due to C.Miehe, N.Apel and M.Lambrecht [13], which is a model of large deformations based on a logarithmic measurement, with a particular duality stress tensor. It is valid regardless of the behavior in small deformations and has the advantage of providing a symmetric tangent matrix. No modification of kinematic internal variables is necessary.