FEATURES OF THE ORIGIN AND DEVELOPMENT OF  CRACKS IN POLYCRYSTALLINE ALUMINUM SAMPLES

doi:10.26565/2222-5617-2024-41-03

E. E. Badiyan V.N. Karazin Kharkiv National University, Svobody Sq. 4, 61022, Kharkiv, Ukraine https://orcid.org/0000-0002-4623-7180
A. G. Tonkopryad V.N. Karazin Kharkiv National University, Svobody Sq. 4, 61022, Kharkiv, Ukraine https://orcid.org/0000-0002-8350-4081
M. R. Shurinov V.N. Karazin Kharkiv National University, Svobody Sq. 4, 61022, Kharkiv, Ukraine https://orcid.org/0009-0003-7660-6519
R. V. Shurinov V.N. Karazin Kharkiv National University, Svobody Sq. 4, 61022, Kharkiv, Ukraine https://orcid.org/0000-0001-6779-1845

DOI: https://doi.org/10.26565/2222-5617-2024-41-03

Keywords: polycrystalline aluminum samples, plastic deformation, destruction, mechanical properties

Abstract

The study investigates the patterns of crack initiation and propagation during the plastic deformation of two-dimensional aluminum polycrystals with different grain sizes. The high-purity (99.96%) research objects are aluminum polycrystals containing only through grain boundaries. The samples were subjected to uniaxial tension at a constant strain rate of at room temperature. An original method based on light diffraction on a quasi-periodic surface structure was used, allowing real-time tracking of crystallographic orientation changes in any region of the sample during plastic deformation and simultaneously recording the initiation and propagation of cracks leading to the destruction of the sample.

Experimental results showed that cracks most often originate at the sample edge due to stress concentration and structural features of the material. Their subsequent development can occur both within the grains and along their boundaries, depending on local deformation conditions, the type, and structure of the grain boundaries. It was found that before a crack forms in a specific region of the sample, significant crystallographic orientation changes occur, which may play a crucial role in the initiation of fracture.

In some cases, the formation of a "torch" of orientation changes – a zone into which the crack propagates, leading to accelerated sample destruction was experimentally recorded. This effect may be related to the redistribution of internal tensions and the activation of plastic deformation in the zone ahead of the crack. The study also documented a rare case of “recrystallization” during deformation, where two adjacent grains "merged into" one due to a change in the crystallographic orientation of one of the grains as a whole during plastic deformation. The ability of entire grains to reorient in two-dimensional samples under plastic deformation was experimentally confirmed in previous studies.

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