Stress limit model with deformation dependent damage for failure prediction in bulk forming processes

Based on the experimental results, a model for the description of damage in materials during bulk forming processes is presented. Unlike the most of the existing models which suppose no damage occurs under compressive stresses, the presented model considers all deformations as the cause for damages. The damages are strongly oriented according to the deformations. Therefore, it cannot be described using just a scalar value. However, failure appears only when the tensile stress exceeds the limit value in the material. In order to perform the failure prediction in FE-simulation of bulk forming processes, an ellipsoid in the stress space is introduced to describe the limit stress. The ellipsoid, or a sphere for an isotropic material, changes its shape according to the deformation applied on the material. The stress state works as the criterion for the rupture in the material.