Failure prediction in anisotropic sheet metals under forming operations using damage theory

摘要

A new damage model which takes account of void shape effect and anisotropy of the matrix material is coupled with a plastic instability criterion. The enhanced criterion proposed in this paper can be used to predict not only the necking limit but also the ductile fracture limit under proportional or non-proportional loading. The model incorporates the effect of void shape, relative void spacing, strain isotropic and kinematic hardening of the base material. The void coalescence failure mechanism by internal necking is also considered by using a modified Thomason's plastic limit-load model. A 3D. F.E.M.. analysis of a unit cube containing an ellipsoidal void is carried out to calibrate the coalescence model. Finally, the proposed plastic instability criterion coupled with damage is used to predict failure of a 5182 aluminium alloy and a Nickel-based alloy Inco 718. The calculated forming limit curves are found to be in a good agreement with the experimental ones.