Numerical analysis of damage for prediction of fracture initiation in deep drawing

The sheet metal may have inherent voids/imperfections present because of preprocessing. These voids/imperfections grow under the applied load resulting into final fracture. The occurrence of ductile fracture is often a limiting factor in metal forming processes. Prediction of the initiation of ductile fracture allows a prior modification of the process which can result in a defect-free final product with financial savings. The intensity of voids is often represented by introducing a variable called damage. This paper deals with the prediction of fracture initiation in deep drawn cup using Lemaitre's continuum damage mechanics model. The damage is incorporated in the constitutive equation through the principle of strain equivalence. The damage is evaluated using the damage growth law proposed by Lemaitre. An in-house 3D finite element formulation is employed for the analysis. The maximum cup height at which the fracture initiates is determined using the critical damage criterion. A parametric study of the maximum cup height is carried out to investigate the influence of material, geometric and other process parameters.