Anisotropic ductile fracture criterion based on linear transformation

An anisotropic ductile fracture criterion is proposed for ductile fracture of lightweight metals. The ductile fracture criterion couples effect of stress triaxiality on void growth, and assumes the shear linking-up of voids governed by the largest shear stress. The criterion is developed based on an isotropic strain rate potential computed from an isotropic damage equivalent strain rate vector, which is mapped from the plastic strain rate vector by a forth order linear transformation tensor. The proposed anisotropic ductile fracture criterion is applied to depict anisotropic ductile fracture of AA 6K21 in shear, uniaxial tension and plane strain tension along different loading directions, and the balanced biaxial tension. The predicted fracture strain and fracture locus are compared with experimental results for the verification of the proposed criterion. The comparison demonstrates that the ductile fracture criterion properly models the anisotropy in ductile fracture under shear, uniaxial tension, plane strain tension and balanced biaxial tension with high accuracy. It shows that the proposed anisotropic ductile fracture criterion can be utilized to predict the onset of ductile fracture in plastic deformation and metal forming of lightweight metals with approximately proportional loading.