PSI - Issue 13

Alexey Evstifeev et al. / Procedia Structural Integrity 13 (2018) 886–889 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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deformation (SPD) techniques (Valiev et al. (1993), Valiev (1996), Sabirov et al. (2013)). But on this way, we should develop new testing methods considering the structural feature of ultrafine-grained materials. The investigation of such materials is complicated by the specific features of small-scale samples currently obtained by SPD methods (for example, disks obtained using the method of High-Pressure Torsion (HPT) are usually up to 20 mm in diameter and up to 1 – 2 mm in thickness). To carry out experiments on high-strain-rate loading, a test method was developed and used taking into account the dimensional features of samples of nanostructured materials. To achieve the goal, a technique was developed and experiments were performed on dynamic tension on model material using drop-hammer impact systems with an accelerator (Evstifeev (2018)). The present work is devoted to results of the study of the behavior of aluminum alloys 1230 ASTM, 5556 ASTM, 2024 ASTM in coarse grain conditions. This information will be foundation for future investigations of dynamic characteristics of these materials in an ultrafine-grained condition.

2. Materials and experimental technique

Experiments were carried out on pure aluminum alloy 1230 (99.3 Al), alloys in the system of Al-Mg (5556) and Al-Cu-Mg (2024). Material properties are presented in the table 1.

Table 1. Materials properties

Al alloy

E, GPa

Average tension strength, MPa

Average microhardness, HV

1230 5556 2024

71 71 71

80

27.7

321 437

113.2

147

For tensile tests, the samples had a working part of 5 mm long and 2 mm wide (Fig.1.a.). The samples were cut by the electrical discharge machine ARTA 123 PRO with high precision. A special holder for small samples was made for dynamic tension experiment (fig.1.b.). Experimental equipment was adopted for tension of small samples in static regime on the Shimadzu tensile machine AG-50kNX and for dynamic tension experiment on the Instron CEAST 9350 drop-hammer. High-energy configuration of the drop-hammer allows to carry out the experiment with the impact velocity from 4.65 to 24.0 m/s. For selected type of samples, it means that strain rate can be more than 1000 1/s.

Fig. 1. The sizes of the sample in mm (a) and the view of mandrel for dynamic tension experiments (b) of small samples.

Test experiments in different loading conditions showed the applicability of the proposed experimental scheme. The signals are stable and can be used to determine the threshold characteristics of the material.

3. Experimental results and theoretical investigation

Experimental results are presented in fig. 2. In the case of a slowly applied force, the tensile strength is equal to the static strength. In the case of dynamic loads, the strength characteristics of materials differ from the static ones. It can be explained by the structure temporal approach in mechanics (Petrov and Utkin (1989), Petrov and Morozov (1994)). Under dynamic loads the time of loading is of the same order as a special time of destruction processes on