On the role of strain rate in in FE-simulation of sheet forming processes

Paper in proceeding, 2008

Strain rate dependency of the sheet material is known to have a delaying effect on the formation of necks in the material. This phenomenon is especially strong in highly ductile steel alloys. The strain rate effect is rarely considered in commercial simulations of forming processes. However, if the purpose of the simulation is to predict strain localization and necking, the strain rate effect has to be considered. In the current paper a simple inverse approach is suggested for the determination of the material’s strain rate dependency. The method assumes that the FLD0, the limit strain at plane strain, is known from some experiment. The material’s strain rate dependency is then determined from simulations of a plane strain test in a trial-and-error process. As a faster alternative to performing full FE simulations, the use of a simple M-K model, consisting of two finite elements, is suggested. Three different functions describing the strain rate hardening effect have been evaluated. The strain rate parameter determined by means of the simplified M-K model has been used in full FE simulations of press forming operations. The FE model is shown to be capable of predicting necking strains in an accurate way.