PSI - Issue 33

M.P. Tretyakov et al. / Procedia Structural Integrity 33 (2021) 1089–1094 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The maximum rigidity of the tooling matches the rigidity of the Instron 8850 testing machine used when using hydraulic grips. Instron 8850 is a versatile two-axis servo-hydraulic testing system that allows tensile-compression tests with a maximum load of 100 kN and torsion with a maximum torque of 1000 Nꞏm. After installing the Belleville springs according to the required scheme, the tooling is installed in the grips of the testing machine in series with the sample. The sample is fixed in the tooling rod by means of a threaded connection. Further, a displacement at a constant speed is applied to the sample, the change in the load is recorded, and the evolution of the deformation field on the surface of the working part of the sample is recorded. 3. Results and discussion As a result of testing according to the method described above, deformation diagrams of Al-Mg alloy samples at different rigidity of the loading system were obtained. Fig. 3 shows a diagram obtained with a loading rigidity of 120 MN / m. Uniform deformation of the specimen is observed up to a stress level of 290 MPa, which corresponds to a smooth section of elastic deformation and the initial stage of hardening. At a stress level in the range of 290 – 300 MPa, the first band of plastic deformation is formed, which is reflected in the diagram as a stress drop. The hardening section of the obtained deformation diagram is characterized by the presence of single teeth associated with the appearance of stripes (Fig. 3, b). At the stage of supercritical deformation, the diagram is characterized by the presence of a large number of closely spaced teeth (Fig. 3, c). Fig. 4 shows a diagram obtained with a loading rigidity of 50 MN/m. Qualitatively, it is comparable for a specimen tested at a stiffness of 120 MN/m, but is characterized by the presence of larger teeth at the supercritical stage of deformation (Fig. 4, b).

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Fig. 3. Tension diagram of a specimen at a nominal stiffness of the loading system of 120 MN/m (a), enlarged sections of the diagram at the stage of hardening (b) and softening (c).