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Streszczenie:
The aim of this research was to investigate an effect of low temperature on the mechanical properties and mi-crostructure of 6061-T6 aluminium alloy (AA6061-T6) subjected to dynamic loading. The specimens were subjected to dynamic compression at a low temperature of −80°C in a range of strain rates from 1.25 × 10 3 1/s to 3.4 × 10 3 1/s to compare their mechanical responses. The deformation mechanisms were analysed through EBSD observations during which dynamic recovery, was found as the dominant one. Furthermore, microstruc-tural analysis indicated that deformation under high strain rate conditions and temperature of-80°C enables to keep the constant initial grain size of the material after the loading applied. The material behaviour was modelled using mechanism-based viscoplastic constitutive equations. Furthermore, an accuracy of the developed model was validated by comparing it to experimental data. The set of constitutive equations proposed has been successful in modelling the stress-strain behaviour of the material for the range of strain rates and temperatures encountered in aluminium-forming processes under low-temperature conditions.

Słowa kluczowe:
Split Hopkinson pressure bar (SHPB),Low temperature,AA6061-T6,Microstructure

Streszczenie:
In this research, an effect of low temperature on the mechanical properties and microstructure of 6061-T6 aluminium alloy (AA6061-T6) subjected to static and dynamic loading was investigated systematically. The specimens were subjected to compression at the temperature of − 80°C in a range of strain rates from 0.001 to 0.1 1/s under static conditions, and from 1250 to 3400 1/s under dynamic conditions to compare their mechanical responses. The deformation mechanisms were discussed based on EBSD analysis. It was found, that under both testing conditions, dynamic recovery was the dominant mechanism responsible for material deformation.

Streszczenie:
The quasi-static and high strain rate compressive behavior of Gum Metal with composition Ti-36Nb-2Ta-3Zr-0.3O (wt pct) has been investigated using an electromechanical testing machine and a split Hopkinson pressure bar, respectively. The stress–strain curves obtained for Gum Metal tested under monotonic and dynamic loadings revealed a strain-softening effect which intensified with increasing strain rate. Moreover, the plastic flow stress was observed to increase for both static and dynamic loading conditions with increasing strain rate. The microstructural characterization of the tested Gum Metal specimens showed particular deformation mechanisms regulating the phenomena of strain hardening and strain softening, namely an adiabatic shear band formed at ~ 45 deg with respect to the loading direction as well as widely spaced deformation bands (kink bands). Dislocations within the channels intersecting with twins may cause strain hardening while recrystallized grains and kink bands with crystal rotation inside the grains may lead to strain softening. A constitutive description of the compressive behavior of Gum Metal was proposed using a modified Johnson–Cook model. Good agreement between the experimental and the numerical data obtained in the work was achieved.

Streszczenie:
Taylor impact tests in the classic and symmetric configurations were applied to analyse the development of plastic deformation and damage in Al-6082-T6 rods. Deformation histories during impact were recorded using high-speed photography, while internal axial damage was identified using metallography. The axial damage observed during the symmetric test were initiated during stress triaxiality peaks under tensile loading conditions. Variations of the stress state are the result of superimposed lateral mechanical waves reflected from the perimeter of the specimen. The fracture strain decreases with the increase of the stress triaxiality; it is thus possible to initiate damage at relatively low strain values under high-stress triaxiality values. During classic Taylor test because of the deflection of the elastic steel anvil in the rod on anvil test, the oscillations are smaller and quickly damped in comparison to the rod on rod experiment. Therefore, the initiation of axial damage is impossible. The cracks on the specimen edge are due to tensile loadings. For both the symmetric and classic Taylor tests, the damage conditions are comparable, i.e., a stable increase of strain combined with tensile loadings.

Słowa kluczowe:
Taylor impact, Numerical modelling, High-speed photography, Damage initiation, Constitutive relation

Streszczenie:
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 × 104 s−1 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.

Słowa kluczowe:
Taylor test, split Hopkinson pressure bar, direct impact compression test, 6082-T6 aluminum alloy, plastic wave propagation