Modeling of Anisotropic Damage for Ductile Materials in Metal Forming Processes

The primary goal of this study is to model the anisotropic effect of ductile damage in metal forming processes. To represent the ductile metals, an anisotropic ductile plasticity/damage formulation is considered within the framework of continuum mechanics. The formulation is motivated from fracture mechanisms and physical observations in Al-Si-Mg aluminum alloys with second phases. The ductile damage mechanisms are represented by the classical ductile process of nucleation of voids at inclusions, followed by their growth and coalescence. Functions of each mechanism evolution are related to different microstructural parameters. The damage, represented by a second rank tensor, is coupled to the Bammann-Chiesa-Johnson (BCJ) rate-dependent plasticity using the effective stress concept. The constitutive equations are integrated using a fully implicit scheme and implemented into a explicit finite element code. This implementation is used to predict damage during the forward axisymmetric extrusion of an aluminum bar. This example illustrates the applicability of the model to predict the initiation and the evolution of anisotropic damage in metal forming processes.