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Cubic shaped specimens with different angles between layer orientation and loading surface were tested quasistatically and dynamically. We found, that shear strength is slightly dependent on the compression load when the angle between layer orientation and load direction is in the range 30-60 degrees and increases 2 times at the angle 750. Material is strain rate sensitive but the behavior of the shear strength is the same at the high strain rates. transversal direction.

This work was inspired by works of Gianfranco D’Anna (2000) where the Portevin-Le Chaˆtelier effect (PLC) was investigated by compressing Al-Mg alloy specimen in a very large deformation range and the results were interpreted from the viewpoint of phase transitions and critical phenomena. Two critical points where deformation process changes from “laminar” to jerky flow and back were noticed. We found that the second critical point where the rate of the serrations is decreased before the macroscopic fracture is not reachable for some alloys even with proposed geometry. We have tested 2 sets of specimens made of the same AMG6 alloy (~6% of magnesium) but with different amount of Si obtained from different producers. Specimens with a higher amount of Si tends to fracture before reaching the second point. Also, we have measured the amount of stored energy which can be recovered as heat during the annealing process. We used the differential scanning calorimeter STA "Jupiter" 449. We found that the amount of this energy sharply increases with the beginning of PLC serrations (first critical point) and drops at a second critical point or at macroscopic fracture. This can be related to a special type of critical phenomena—structural scaling transitions in mesodefect ensembles and associated structural relaxation mechanisms Naimark (2016)

The purpose of this work is to provide theoretical framework and experimental supporting evidence for a crucial role of structural transitions in the ensemble of defects at the meso-level (microshears and microcracks), as one of the mechanisms of plastic strain localization in metals under high-rate loading. The investigation of the sample response to dynamic loading was carried out on the split Hopkinson pressure bar and in a series of target penetration tests. To identify the characteristic stages of strain localization, the thermodynamics of the deformation process was investigated "in-situ" by recording the temperature fields using a high-speed infrared camera CEDIP Silver 450M. The temperature measured in the localization zone does not confirm the generally accepted concept of the strain localization mechanism as the mechanism governed by a thermoplastic instability. The samples stored after the experiment were subjected to microstructural analysis, using an optical interferometer-profilometer and a scanning electron microscope. The structural analysis revealed a correlated behavior of the ensemble of defects, which can be classified as a structural transition providing strain localization. The data of experimental studies, the examination of the structure of deformed samples, as well as the data of numerical modeling taking into account the kinetics of accumulation of microdefects in the material suggest that one of the mechanisms of plastic strain localization at high loading rates is associated with the jump-like processes in the defect structure of a material.

The effects of loading intensity and material structure on statistical regularities of fragmentation were studied. The material under investigation is zirconia-based ceramics. The samples with different pore structure (10%, 20%, 30%, 45%, 60% - the porosity of the powder used for ceramic sample sintering) were tested. The experimental data on dynamical fragmentation of ZrO2 ceramics allowed us to construct the fragment size distribution (spatial scaling) and the distribution of time interval between fractoluminiscense pulses (time scaling). The power law exponent of spatial scaling depends on ceramics porosity and intensity of loading, which has a considerable influence on the power law exponent for samples with highest porosity (60%). Two types of the distribution function for time interval were observed. For ceramics of low porosity (less than 60%) the distribution is fitted by two power laws with different exponents, and the distribution of time intervals for ceramics of highest porosity (60%) obeys one power law. An increase in porosity leads to the growth of the number of single fracture events (the number of middle and short intervals), as a consequence of missing the second power law exponent. Statistics of pore systems in two samples with 20% and 60% porosity was studied using X-ray Computed Tomography (CT). Analyzing more than a thousand of cross section images for every sample, we get a cumulative pore area distribution, and a relationship between area and perimeter. The best fitting for pore area distribution are: 1) two power laws for sample with highest porosity (60%); 2) double exponential law for low porosity (20%). The area – perimeter relation satisfies a power law.