Characterization and prediction of fracture in 6000-and 7000-series aluminum alloy sheet under various stress states

This study investigates the stress state dependent fracture of several high strength aluminum sheet alloys, AA6013-T6, AA7075-T6 and a developmental AA7xxx-T76 alloy. These alloys are targeted for use in automotive structural applications for which accurate knowledge of the fracture loci are required to support crash safety simulations. A generalized Drucker-Prager (GDP) model to describe the fracture locus was proposed and calibrated to the measured fracture strains under simple shear, uniaxial, plane strain and biaxial tension. Calibration of the fracture loci was undertaken directly using measured fracture strains and direct integration of stress based on the measured strain histories. The calibrated fracture loci using the GDP function exhibited good agreement with the measured data across the range of the stress state conditions. An advantage of the GDP model is the admission of fracture asymmetry in uniaxial and biaxial tension which is not captured using the Hosford-Coulomb model. The experimental fracture loci were then paired with a damage model for non-linear strain paths and used to simulate three-point bend experiments on structural hat channel sections. For each material, the load response and onset of fracture were well predicted.