Anisotropic behavior in plasticity and ductile fracture of an aluminum alloy

Anisotropic mechanical behavior is investigated for AA 6K21-IH T4 in both plastic deformation and ductile fracture. Anisotropic plastic deformation is characterized by uniaxial tensile tests of dog-bone specimens, while anisotropy in ductile fracture is illustrated with the samples with a central hole, notched and shear specimens. All these specimens are cut off at every 15° from the rolling direction. The r-values and uniaxial tensile yield stresses are measured from the tensile tests of dog-bone specimens. Then the anisotropic plasticity is modeled by a newly proposed J2-J3 criterion under non-associate flow rule (non-AFR). Ductile fracture is simulated to extract the maximum plastic strain at fracture strokes as well as the evolution of the stress triaxiality and the Lode parameter in different testing directions. The measured fracture behavior is described by a shear-controlled ductile fracture criterion proposed by Lou et al. (2014): (Modeling of shear ductile fracture considering a changeable cut-off value for stress triaxiality. Int. J. Plasticity 54, 56-80) for different loading directions. It is demonstrated that the anisotropic plastic deformation is accurately described by the J2-J3 criterion along various loading conditions including shear, uniaxial tension and plane strain tension. Moreover, it is shown that the anisotropy in ductile fracture is not negligible and cannot be modeled by isotropic ductile fracture criteria. Therefore, an anisotropic model is highly recommended to accurately illustrate the directionality in ductile fracture.