Identification method for anisotropic and high strain rate plasticity of sheet metals based on heterogeneous highspeed inertial impact and principle of virtual work

High-strength lightweight alloy sheets. such as 2024 wrought aluminum alloy sheets, are widely applied in aeronautic and astronautic industries as essential structural materials. The anisotropic plasticity induced by the rolling process and the strain rate sensitivity under impact loadings significantly affect their dynamic deformation behaviors, which make it difficult to accurately predict the material response during complex forming process or under extreme service conditions. Currently, the characterization of dynamic mechanical properties of materials mainly relies on the classical split Hopkinson pressure bar. It is based on the assumption of uniform deformation and one-dimensional stress wave propagation, which lead to the shortcomings of large number of required tests for comprehensive anisotropic plasticity, difficulty in characterizing coupling effect as well as in extracting parameters at early yielding stage. In this paper, a new method for the simultaneous characterization of the anisotropic and strain rate-related plasticity parameters is proposed based on the heterogeneous inertial fields obtained from the highspeed impact of a nonuniform specimen and the virtual fields method. Specifically, by designing and conducting the virtual highspeed impact test of a double-notched specimen, the comprehensive stress-strain state of the specimen can be manipulated and the simulated heterogeneous strain, strain rate and acceleration field data at the inertial acceleration stage obtained. Then, the dynamic constitutive parameter identification algorithm is developed based on the principle of virtual work, using which the multiple anisotropic and strain rate-related dynamic plasticity parameters of the specimen are accurately characterized at the same time from the single virtual heterogeneous impact test. Also, the influence of the state variables such as the boundary conditions, impact loading modes on the identification accuracy is analyzed. The proposed method shows its merits in minimizing the required tests for identifying such comprehensive constitutive models and releasing the limitations suffered by conventional dynamic testing methods.