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

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