Finite element analysis of damage evolution and the prediction of the limiting draw ratio in textured aluminum sheets

Void nucleation and growth models have been incorporated into an elasto-plastic finite element code together with an anisotropic fourth-order strain rate potential so that damage evolution during the deep drawing of textured aluminum sheets can be analyzed. The fourth-order strain rate potential is based on the Taylor model of crystal plasticity and therefore takes the presence of texture into account. The damage evolution is modeled in terms of void nucleation and growth during deformation. Strain-induced and stress-controlled nucleation models were employed in conjunction with the Cocks and Ashby growth model to calculate the increase in void volume fraction. The influence of plastic anisotropy on damage is discussed together with the roles of void nucleation and growth on damage evolution for cold rolled and cold rolled annealed aluminum sheets. It is shown that the growth of voids as opposed to their nucleation plays a very important role in damage formation during the development of localized necks. More attention should therefore be paid to void nucleation and growth in the analysis of localized necking and fracture during sheet metal forming.