PSI - Issue 50

Alexander Inozemtsev et al. / Procedia Structural Integrity 50 (2023) 119–124 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Intrudiction The phenomenon of plastic strain localization, i.e. the formation of narrow regions of plastic flow, in which the level of plastic strain is orders of magnitude higher than in the surrounding material, is of theoretical and practical interest. The localization of plastic strains in metals at different loading rates is a complex process, which depends on the rate and magnitude of deformation, temperature, as well as evolution of the material structure. This phenomenon has been investigated by Giovanola J. H. (1988), Marchand A., Duffy J. (1988), Rittel D. at al. (2008). At present, there are two generally accepted views on the mechanisms of strain localization: thermoplastic instability, which occurs at high strain rates, and mechanisms related to structure evolution, which can be realized over a wide range of loading rates. In addition to thermoplastic instability, which arises at high strain rates, the structural transitions in ensembles of mesolevel defects (microshifts and microcracks) also significantly contribute to the process of strain localization. The purpose of this work is to justify the mechanism of plastic strain localization associated with a specific type of critical phenomenon (structural-scale transition) in the ensemble of defects, which was first established by The split Hopkinson pressure bar (SHPB) tests were performed to investigate the mechanisms of plastic strain localization under conditions of dynamic loading of specimens made of AlMg6 aluminium alloy, which exhibits tendency to plastic flow instability. To study the processes of plastic strain localization in the predominant shear mode under conditions of dynamic loading on the split Hopkinson pressure bar, we developed and patented special-shaped (U-shaped) specimens and tooling ensuring the realization of the plane strain state, Bilalov D.A .at al. (2018). All sections parallel to the lateral surfaces and drawing plane (Fig.1b) are in the close stress-strain states. This observation is confirmed by the results of numerical simulation, Sokovikov M.A. at al. (2020). In order to identify characteristic stages of strain localization and development of localized shear fracture under dynamic loading we investigated thermodynamics of the deformation process based on the results of in-situ recording of temperature fields with a CEDIP Silver 450M high-speed infrared camera. The main technical characteristics of the camera are as follows: sensitivity is no less than 25 mK at 300°K, spectral range is 3 -5 μ m, maximum frame size is 320x240 pixels, spatial resolution ("pixel size") is ~ 0.2 mm, temporal resolution is ~ 0.25 ms. In Bilalov D.A .at al (2018), it is shows that at strain rates (~10 3 s -1 ) and higher, the characteristic times of thermal conductivity for AlMg6 alloy are significantly longer than the characteristic times of the deformation process. The analysis of temperature fields on the lateral surface in real time, allowed us to draw conclusions about the distributions of temperature fields and plastic strains in all sections parallel to the lateral surface. The specimen geometry, schematic representation of the dynamic experiment and results of testing are shown in Figure 1. Naimark O.B., (2003). 1. Experimental study