Influence of Pre-Deformation on Springback Effect of Advanced High Strength Steel

In sheet metal forming process of automotive components,the springback effect is significant,in particular for Advanced High Strength Steels (AHSS),for example the Dual Phase (DP) steel.Most of construction parts of modern vehicles have very complex shapes and therefore multi-step procedures are necessary to form such a part.Steel sheets,which firstly undergo pre-deformation,can show considerable change in mechanical behavior during the forming process.However,at present there are limited sufficient data concerning pre-deformation effect on the springback available.In this work,a study of influences of different pre-strain levels on the springback of steel sheet made of AHSS materials has been carried out.The sheet specimens were firstly pre-stretched on a tensile testing machine and the pre-strain values were calculated based on the engineering strain.Furthermore,the steel sheets prepared parallel,transverse,and 45° to the rolling direction have been investigated.A modified U-shape forming was used to evaluate the degree of springback of the steel sheets under various conditions.In parallel,FE simulation of the U-shape forming was performed.Both isotropic model using stress-strain responses from tensile test of specimens with different directions and anisotropic Hill’s 48 model have been applied.The experimental results are compared with the sheet metal forming FE simulations.The primarily aim is to basically understand the springback mechanism by means of the simple models.And finally,conclusions with regard to the springback modeling will be presented.