The effect of intermetallic inclusions on the formation of subsurface cracks in the AlMg6 alloy under very high cycle fatigue

D.A. Bilalov, V.A. Oborin, O.B. Naimark show affiliations and emails
Received 23 January 2020; Accepted 19 March 2020;
This paper is written in Russian
Citation: D.A. Bilalov, V.A. Oborin, O.B. Naimark. The effect of intermetallic inclusions on the formation of subsurface cracks in the AlMg6 alloy under very high cycle fatigue. Lett. Mater., 2020, 10(2) 206-210


The fracture surface of the material with the formation of cracks in the volume of the sampleThe article discusses the process of deformation and fracture of the AlMg6 alloy (a material for aircraft engine building) under very high cycle fatigue. The choice of research material is substantiated, a description of its chemical composition is given. The geometry of samples for fatigue testing, loading conditions and characteristics of testing machines are given. For fatigue tests, a Shimadzu USF-2000 ultrasonic machine was used. Preliminary dynamic loading was carried out on a split Hopkinson-Kolsky bar. A series of experiments on the fatigue failure of the AlMg6 alloy was carried out, including after preliminary dynamic loading. Analysis of the fracture surfaces revealed two characteristic types of subsurface cracks. Chemical analysis showed that in the first case, the intermetallic inclusion is the focus of destruction, since a change in the percentage ratio of aluminum and magnesium in the test material was observed. In the second case, such a change was not observed, therefore, a conclusion is drawn according to which the internal defect served as the focus of destruction. A mathematical model is proposed for describing the deformation behavior of metals and alloys, based on the statistical theory of defects. Particular attention is paid to the selection of the destruction criterion. The conditions are imposed that the fracture criterion under cyclic loading must satisfy. A criterion is constructed based on the critical value of the accumulated energy. The ideology of determining unknown model parameters is proposed. Identification of unknown parameters was carried out. A number of computational experiments were carried out. The calculations are in good agreement with the experimental data. It is shown that the proposed mathematical model is capable of predicting the fatigue failure of the material under study, taking into account preliminary dynamic effects based on 10^6 –10^9  cycles.

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