In this work, the viscoplastic behaviour of 6082-T6 and 7075-T6 aluminium alloys is examined over a wide range of strain rates. Three different testing techniques were applied to this investigation: low-rate experiments were performed using a regular servohydraulic testing machine, high-rate tests were conducted using a split Hopkinson bar apparatus and very-high-rate experiments were carried out using a miniaturised direct impact test arrangement. The latter testing set-up allowed for the characterisation of material flow at strain rates up to _ e % 4 Á 10 4 s À1 . These experimental results showed a sharp increase in the rate sensitivity of the materials once a threshold loading rate of _ e % 5 Á 10 3 s À1 is exceeded. This behaviour may be attributed to the presence of viscous drag on high-velocity dislocation motion. In addition, the thermo-viscoplastic behaviour of the 6082-T6 and 7075-T6 aluminium alloys was analytically described using the extended Rusinek-Klepaczko model of viscous drag effects. Satisfactory correlation was observed between the experiments and the constitutive model results over the entire range of strain rates studied, 4 Á 10 À4 s À1 < _ e < 4 Á 10 4 s À1 .
The analysis involved subjecting DP 500 steel to pre-fatigue loads, and then tension at high strain rates using Hopkinson bar. Digital image correlation method was used to investigate how the pre-fatigue loads change the strains' distribution on the surface of the sample subjected to tension. The analysis involved both films recorded at low rates of deformation (1.0 3 10 22 s 21) using ARAMIS system and the images captured with a high-speed camera during dynamic deformations with a Hopkinson bar (6.0 3 10 2 s 21). It was noted, based on the micro-structural analysis, that pre-fatigue loads cause the formation of micro-damages in the examined material. Thus, macroscopically observed stress-strain characteristic as well as Huber-Mises substitute strains' distribution determined locally by the image correlation method is also subject to changes. The observed effects include the following: reduction of deformation corresponding to the tensile strength, decrease in elongation at break, and increase in yield limit and tensile strength. The observed effects are intensified with an increased stress value and pre-fatigue cycles' number. Furthermore, these phenomena are more intensive in the conditions of dynamic deformation.
The application of an extended Rusinek-Klepaczko constitutive equation to predict the mechanical response of 6082-T6 aluminum under the Taylor impact test conditions was presented in this article. The numerical results obtained in the study were verified through a comparison with the experimental data extracted from the Taylor anvil-on-rod impact experiments. It was concluded that the extended Rusinek-Klepaczko constitutive model predicts the behavior of the tested aluminum alloy under applied loading conditions with satisfactory accuracy. Moreover, it was found that the plastic wave phenomenon in this material is very limited and that there was no region of constant plastic wave velocity. Strain rates up to 1.6 3 10 4 s 21 were recorded during the Taylor impact experiments; therefore, this value may be set as the upper limit of the extended Rusinek-Klepaczko model for the alloy, which was validated with the anvil-on-rod experiment.
The paper presents the results of the analysis of the striker shape impact on the shape of the mechanical elastic wave generated in the Hopkinson bar. The influence of the tensometer amplifier bandwidth on the stress-strain characteristics obtained in this method was analyzed too. For the purposes of analyzing under the computing environment ABAQUS / Explicit the test bench model was created, and then the analysis of the process of dynamic deformation of the specimen with specific mechanical parameters was carried out. Based on those tests, it was found that the geometry of the end of the striker has an effect on the form of the loading wave and the spectral width of the signal of that wave. Reduction of the striker end diameter reduces unwanted oscillations, however, adversely affects the time of strain rate stabilization. It was determined for the assumed test bench configuration that a tensometric measurement system with a bandwidth equal to 50 kHz is sufficient.
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