A modified elliptical fracture criterion to predict fracture forming limit diagrams for sheet metals

The purpose of present research is to predict fracture loci containing fracture forming limit diagrams (FFLDs) in sheet metal using a modified elliptical fracture criterion based on two kinds of strain energy density (SED), i.e. distortional and volumetric SED. The fracture loci of AA2024-T351 in strain spaces were constructed to calibrate the fracture criterion by using open experimental data since the ductile fracture behavior of AA2024-T351 was extensively investigated. In addition, the effect of intrinsic parameter a which is the ratio of critical shear fracture stress to critical normal fracture stress on the fracture loci was studied. Then, the calibrated fracture criterion was utilized to predict the FFLDs of AA7050-17451. Experiments and simulations of uniaxial tension, pure shear, notch tension and flat-groove tension specimens covering a wide range of stress triaxiality were investigated to verify the predictive ability of FFLDs. It is found that the fracture locus of AA2024-T351 is in accordance with the open experimental data and the predictive ability of FFLDs for AA7050-T7451 is verified by fracture strains of the four specimens.