Modeling Anisotropic Ductile Fracture Behavior of Sheet Metals Considering Non-directionality of Equi-Biaxial Tensile Fracture

An accurate characterization of fracture behavior under pure shear, uniaxial tension, plane strain tension, and equi-biaxial tension plays a vital role in high-fidelity numerical simulation of the sheet metal forming. From a plastic deformation viewpoint, the non-directionality of the equi-biaxial tensile fracture is the inherent characteristic of sheet metal. However, little attention has been paid to modeling the non-directionality of the equi-biaxial fracture strain. This paper develops a new anisotropic ductile fracture model by including an empirical weight function into the DF2014-based fracture criterion to consider the non-directionality of the equi-biaxial tensile fracture. Then, the proposed model is utilized to depict the anisotropic ductile fracture behavior of DP980 steel, AA6082-T6 aluminum alloy, and Ti-6Al-4 V titanium alloy to verify its fracture predictability under various stress states. The prediction results are compared with the DF2014 and DF2016-based criteria. The results show that the proposed model correctly captures the non-directionality of equi-biaxial tensile fracture strain and depicts the anisotropic ductile behavior of these metals with high accuracy under proportional loading conditions. Meanwhile, the proposed model provided a similar fracture prediction accuracy to the DF2016-based criterion for different metal sheets, which indicated that the fracture predictability of this model had been successfully enhanced. In addition, finite element analysis for the square cup drawing test of AA6016-AC200 alloy is conducted in ABAQUS/Explicit to validate its performance under non-proportional loading conditions. The simulation results of the punch force–stroke curve and fracture shape in good agreement with the experimental measurements. The comparison study demonstrates that the proposed anisotropic ductile fracture model provides quite accurate predictability in depicting the anisotropic ductile fracture behavior of different metallic materials. Accordingly, the proposed model is recommended to be applied in FE simulation to improve the reliability and accuracy of numerical design and optimization of metal sheets product and forming process.