Finite Element-Based Modeling of Strain Hardening in Metal Forming

Strain hardening in cold metal forming occurs as a result of impeded dislocation movements. It is one of the key advantages of cold metal forming, since it increases the fatigue strength and load capacity of components. As a consequence, strain hardening is an important design feature. The state of the art quantitative prediction of the strain hardening is possible if precise values of the strain rate, temperature, and effective strain of the forming process are known and the appropriate flow data exists. This work introduces a practicable way of modeling strain hardening based on an FE analysis in DEFORM. The modeling is realized by a user subroutine that computes the current and initial flow stress. The approach can be applied to any flow curve formulation. This work, however, exemplifies the complex case of tabulated temperature- and strain-rate-dependent flow stresses. The computation of strain hardening is shown on a three-shouldered cold solid forward extrusion process and verified by experimental micro hardness tests.