Simulation of the sheet metal extrusion process by the enhanced assumed strain finite element method

The extrusion process of a steel plate has been simulated by the geometrically non-linear enhanced assumed strain finite element method. An enhanced strain field has been added to the conventional axisymmetric four nodes element to avoid volumetric locking in the plastic range. In order to achieve volume constraint closely, the enhanced deformation gradient has been constructed in the rate form. The standard Newton-Raphson iteration method together with the corresponding consistent tangent operator have been used to solve the incremental equilibrium equations. The local integration of the finite strain J2-flow theory has been carried out by the elastic predictor and plastic corrector return mapping algorithm. The material constitutive equation used takes the effects of strain hardening and damage softening into account. In the solution process, a line search technique has been used to ensure computational convergence. The computed profile of the protruded workpiece has been found to be in good agreement with the actual profile. The results also show that damage softening has a remarkable influence on the limit strain of the extrusion process. It may be concluded that the enhanced assumed strain finite element method can be used to analyze sheet metal extrusion.