Cryogenic fracture modeling and prediction of Al-Cu-Mn alloy sheet

Cryogenic ductile fracture model is important for guiding forming processes under complex stress and cryogenic temperature conditions. However, it is challenging to obtain reliable cryogenic fracture strains under biaxial tension and shear stress states. The elevated cryogenic friction exacerbates localized deformation in the traditional rigid punch bulging test. Serious torsion occurs in shear specimens due to the significantly enhanced hardening ability at cryogenic temperatures. Therefore, a free bulging device pressurized by liquid nitrogen was developed to obtain cryogenic fracture strains under a biaxial tensile stress state. A novel two-step hybrid method that accounts for edge damage was proposed to obtain cryogenic fracture strains under the shear stress state. The cryogenic fracture loci were established based on the advanced Lou-Huh fracture criterion using reliable cryogenic fracture strains under uniaxial tension, plane strain, shear, and equi-biaxial tensile stress states. Finally, a cryogenic material model framework, including non-associated anisotropic plasticity and ductile fracture, was applied in finite element analysis to predict fracture. The results showed that the proposed methods accurately determined the cryogenic fracture strains. The fracture strains of AA2219 at -196 °C under equi-biaxial tension and shear stress states were 0.7983 and 1.4460, which were 53.4% and 50.6% higher than those at room temperature. The developed cryogenic model framework for AA2219 effectively predicted the failure initiation location, morphology, and stroke under complex cryogenic stress states. Comparative experimental results showed that the deviation in the predicted failure stroke was less than 5.2%. This study provides a reliable modeling approach for optimizing cryogenic forming processes involving aluminum alloys.