Material modelling for accurate springback prediction

Abstract

The magnitude of the springback depends mainly on the residual stresses in the work piece after the forming stage. An accurate prediction of residual stresses puts, in turn, high demands on the material modelling during the forming simulation. Among the various ingredients that make up the material model, the hardening law is one of the most important ones for an accurate stress distribution prediction. The hardening law should be able to consider some, or all, of the phenomena that occurs during bending and unbending of metal sheets, such as the Bauschinger effect, the transient behaviour, permanent softening and work-hardening stagnation. Five different hardening models and four different steel grades have been evaluated in the present investigation. The unknown material parameters were identified by inverse modelling of a three point bending test. The model’s ability the reproduce experimental force-displacement relationships were evaluated. A simple springback experiment was performed for confirmation.