| Resumo: | During the last decade, several commercial codes were developed to meet the increasing demands from industry to evaluate deformation paths as well as forming defects, in order to avoid the long and expensive tryout in press shops. Although these numerical codes have reached a high accuracy in the evaluation of forming defects, the accurate prediction of a necking initiation is still a largely open question. The traditional method for failure prediction is to perform a comparison of the material points principal strains with the Forming Limit Diagram, obtained under proportional in-plane loading. Although this kind of analysis is reliable for simple cases, when complex strain paths and anisotropy are involved, this approach may fail to give the right answer due to the strong dependence of the Forming Limit Diagram level in respect to the strain and stress history. Alternatively, prediction of failure for complex parts stamping can be made by post-processing the numerical solution using a Plastic Instability Model such as the widely used localization approach proposed by Marciniak and Kuczincki coupled with the conventional theory of Plasticity [1]. Another promising approach is to consider a continuum damage model that describes the internal material degradation due to micro-defects that occur during plastic loading and, therefore, can establish a limit for plastic deformation of a part in forming operations. Within this framework, a continuum damage model is implemented in a commercial code, fully coupled with an orthotropic plasticity criterion. The resulting constitutive equations are implemented and assessed for the prediction of fracture onset in sheet metal forming processes. An experimental failure case is presented to demonstrate the applicability of the implemented model in the necking prediction in sheet metal forming processes. Corresponding numerical simulation is performed and its results compared with experimental ones for a selected material.
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