Damage based formability analysis of sheet metal with LS-DYNA

This papers presents a damage mechanics model, which was proposed recently by the authors for predicting the localized necking and final failure of sh eet metals. It is generalized to take into account the continuous direction al change of principal strain plane and damage plane, and their hysteretic effect on damage evolution. The generalization is a critical requirement to predict accurately the forming limit strains, as most stamped components a re subjected to multistage forming process. This type of forming process pr oduces non-proportional stamping force/load and a complex strain history in the stamped part causing directional change of principal strain plane and damage plane. The damage model is implemented into the large-scale finite e lement package LS-DYNA that then was applied to pl edict the forming limit strain and fracture limit strain of VDIF under non-proportional loading con dition. Satisfactory predictions have been achieved for several case exampl es where the complex strain histories are prescribed from a practical stamp ing operation.