Dynamic Mechanical Properties And Damage Evolution Of High Purity Aluminum

In this paper, the dynamic and quasi-static compression and tension tests and the plate impact spallation experiments were performed on the high-purity aluminum samples with three different grain sizes. By using microscopic observations and numerical simulation, the dynamic mechanical properties and the basic laws of damage evolution of high-purity aluminum were studied.1.The high-purity aluminum specimens with grain size of 243,678 and 1070μm were produced by heat treatment.2.The compression and tension tests of high strain rate (102~103s-1) and low strain rates (10-3~10-2s-1) on three samples of high-purity aluminum were carried out by using experimental apparatus of SHPB(SHTB) and MTS universal testing machine. The compression and tensile properties of high-purity aluminum samples are not only sensitive to strain rate but also very sensitive to the grain size. The linear Hall-Petch equation is applicable to describe the the relationship between flow stress and grain size in dynamic compression and tensile loading conditions. However, the Hall-Petch coefficients are different for dynamic loading condition and the quasi-static loading condition, which are related to the strain and strain rate.3.Based on the experimental results, the relevant parameters of Johnson-Cook (JC) constitutive model for high purity aluminum samples were obtained. The fitted curves agree with the experimental ones very well,and find that as the grain size increases, the initial yield stress and strain hardening coefficient decreases, while the strain rate sensitivity increases.4.Spall tests were performed on the three high-purity aluminum samples by plannar impact loading.The spall signal can be seen clearly on the history of stress obtained from the experiment. The influence of grain size on the spall properties of high-purity aluminum is negligible. Metallographic observations on the recovered samples show that the fracture of high-purity aluminum is in the way of nucleation, growth and coalescence of voids.5.The numerical simulation were carried out on spallation experiments with the LS-DYNA . Simulated stress profiles by the maximum tensile stress model and model of T-B damage accumulation have the same trend with the experimental results, but there is a obvious difference for subsequent stress oscillations after spallation. The reason is that numerical simulation did not consider the influence of damage on the material constitutive equation.