Investigation of Fracture Behavior of Deep Drawn Automotive Part affected by Thinning with Shell Finite Elements 2020-01-0208
In the recent decades tremendous effort has been made in automotive industry to reduce vehicle mass and costs in order to improve fuel economy and develop safer vehicles than any other decades.
An accurate modeling approach of sheet metal fracture behavior under plastic deformation is one of the key parameters affecting optimal vehicle development process. FLD (Forming Limit Diagram) approach which plays an important role in judging forming severity has been widely used in forming industry and localized necking is the dominant mechanism leading to fracture in sheet metal forming and crash events.
FLD is known as limited only to deal with the onset of localized necking and could not predict shear fracture. Therefore it is essential to develop accurate fracture criteria beyond FLD for vehicle development. To enhance the accuracy of crash simulations, forming results from stamping process are generally introduced to consider work hardening and thinning/thickening of a stamped part during the simulations. However fracture criteria is only applied to the original design thickness not thinned or thickened gage after forming process. It causes inaccurate fracture prediction on 2D Shell elements.
How to create HC fracture model from existing FFLD curves is demonstrated in this paper and the developed FFLD (Fracture Forming Limit Diagram) ,which covers ultimate cracks beyond local necking, based on traditional FLD enabling to predict fracture of CR340HSLA steel on deep drawn seat belt anchor plate under tensioning load is investigated and compared to corresponding GISSMO(Generalized Incremental Stress State dependent damage Model) using Triaxial Limit by a new keyword(*DEFINE_CURVE_TRIAXIAL_LIMIT_FROM_FLD) in LS-DYNA3D which is being converted from FFLD and developed by HC(Hosford-Coulomb) fracture model. And the thinning effect on 2D-shell elements by deep drawing affecting fracture behavior is also investigated.
Finally a proposed approach to predict accurate fracture considering thickness changes during forming on deep drawn parts by FFLD is validated to corresponding experiments.