An improved physical damage model incorporating stress state effect for aluminum alloys

Aluminum alloys are typical lightweight metallic material, and their fracture behavior has attracted significant attention in the automotive and aerospace industries. In our investigation, a stress-state-dependent void nucleation strain was derived based on the maximum principal stress nucleation criterion and the Johnson-Cook (JC) constitutive model. Moreover, a improved physical damage model incorporating stress-state effects was established based on it. Its parameters were fitted using the void results in the ”strain freezing” experiments. Subsequently, the dynamic fracture behaviors of 5052 and 2024 aluminum alloys under different loading stress states (uniaxial tensile, tensile-shear mixed plane strain state, plane strain states with high stress triaxiality, and pure shear state) were investigated using Split Hopkinson Pressure Bar (SHPB). The improved physical damage model and four widely used traditional damage models were applied to numerically calculate the dynamic fracture behaviors for these cases. The new damage model successfully captured the macroscopic fracture morphologies, force–displacement curves, fracture strains (maximum error of −11.64%), and microscopic void ellipticity on fracture surfaces (maximum error of 13.08%) under different stress states of two aluminum alloys. Compared to traditional damage models, the new damage model not only had clear physical significance, but also exhibited higher predictive accuracy in fracture strain (average errors are 3.59% and 4.87% for 5052 and 2024 aluminum alloys). Moreover, the fracture initiation and propagation under tensile-dominated or shear-dominated loading were insensitive to the ductility for aluminum alloy. However, their fracture initiation and propagation exhibited notable differences under tensile-shear mixed loading.