Springback simulation in metal sheet forming

Springback prediction is an important issue for the sheet metal forming industry. The application of new materials, including high strength steel, for light weight structures in the automotive industry is often impeded by the insufficient predictability of the springback effect. The prediction of springback during sheet forming requires the exact calculation of the stress distribution in the sheet. Most sheet metal elements undergo a complicated cyclical deformation history during the forming process. For an accurate prediction of springback, the Bauschinger effect must be considered to determine accurately the internal stress distribution within the sheet after deformation. 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.