Predicting Sheet Metal Fracture Surface in AA 6xxx using Anisotropic Continuum Damage Mechanics Model

A new Anisotropic Time-Dependent Continuum Damage Mechanics Model is proposed to predict the fracture surface of AA 6xxx metal sheets. Accurately predicting fracture behavior under complex stress states is a challenging problem in metal-formed structure design. In general, sheet metals exhibit anisotropy in both deformation and fracture behavior, with the stress state at fracture being affected by the type and direction of loading. This study first examines the mechanical and fracture behavior of AA 6xxx sheets through tensile testing with varying specimen geometries. Strain distribution at the point of fracture was captured using digital image correlation. The constitutive model was implemented in commercial finite element software as a user subroutine and calibrated using a hybrid approach combining experimental results, boundary value analysis, and Nelder – Mead optimization. The prediction capability of the proposed constitutive model and calibration approach was assessed using various stress states condition. The 3D fracture surface was then constructed based on the simulated fracture point, lode angle, and stress triaxiality.