Spring-back simulation based on characterization of sheet metals under reverse plastic strains

The application of new sheet materials is often impeded by the insufficient predictability of the spring-back complicated by the Bauschinger effect. The prediction of spring-back during sheet forming requires the exact calculation of the stress distribution in the sheet after one or more cycles of reverse plastic deformations. A Chaboche-type combined hardening model has been used to enable such calculations. The required material parameters have been determined from cyclic stress-strain curves measured in tension-compression tests. In order to facilitate those tests also with thin sheet specimens, a special testrig and a new specimen design have been developed. A Chaboche-type combined hardening model has been invoked through the user subroutines in a commercial finite element (FE) code. A number of studies from simple hat profiles to rather complex real automotive parts in cooperation with different industrial partners have been performed. Besides different steel sheets, sheet magnesium alloy MgAZ31 has been investigated.