A new approach for fracture prediction considering general anisotropy of metal sheets

One of the most challenging issues in the automotive industry is to reliably predict the fracture limits across a broad range of the deformation modes subjected to various forming processes. Sheet metals in general exhibit anisotropy in both their deformation and fracture behaviors, and accordingly the stress and strain states at fracture strongly depend on both the loading condition and direction. A primary concern here is that there exists no global tendency of the anisotropic fracture limits over the wide range of the loading conditions, which gives rise to a difficulty in modeling the anisotropic fracture criterion. In this paper, a solution to the challenge of modeling anisotropic fracture behavior is proposed based on a decoupled formulation of anisotropic fracture limits with an employment of a Lagrangian interpolation function and an L-2-norm of the principal stress vector. The anisotropic fracture criterion developed based on the proposed modeling approach was successfully applied to accurately represent the fracture forming severity of the DP980 with a thickness of 1.2 mm over a wide range of the loading condition including inplane shear, uniaxial tension, plane strain tension, and equi-biaxial tension. Comparison of the experimental results with the predictions of the proposed criterion revealed that the proposed criterion has a remarkable capability in describing the anisotropic strain- and stress-based fracture limits. In addition, it was also theoretically discussed how the proposed modeling approach can be extended to predict fracture even for fully anisotropic materials without any plane of symmetry on the fracture initiation.