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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 phenomenon of plastic strain localization in alloys under dynamic loading was experimentally studied on a Hopkinson–Kolsky bar and during target penetration tests. The temperature fields generated during deformation were studied in situ using a CEDIP Silver 450M high-speed infrared camera with the aim to identify the characteristic stages of localized shear. The temperature field distribution obtained at different time allowed us to trace the evolution of plastic strain localization. Microstructural analysis of the post-test samples was carried out using an optical interferometer-profilometer and electron microscopes. The structural analysis provided evidence for the correlated behavior of the ensemble of defects, which can be classified as a structural transition responsible for the strain localization. The results of experimental studies, the study of the deformed sample structure, as well as the data of numerical simulation made with consideration for the evolution of microdefects in the material, suggest that one of the mechanisms of plastic strain localization in alloys under high-speed loading is caused by jump-wise processes in the defective structure of materials.

Experimental studies on the response of samples to dynamic loading were performed using a split Hopkinson-Kolsky bar and in a series of perforation tests. In-situ investigations of the thermodynamics of deformation processes made it possible to identify the characteristic deformation localization stages. Temperature fields were recorded with a high-speed infrared camera CEDIP Silver 450M, and strain localization in the samples was evaluated with a strain noninvasive measurement system StrainMaster. Temperature measurements made in the localization zone did not support a generally accepted concept that the strain localization mechanism is the mechanism governed by thermoplastic instability. The microstructural analysis of the samples stored after the experiment was carried out using an optical interferometer-profilometer and a scanning electron microscope. The analysis revealed the 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 performed with consideration of 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 the material.

The behavior of specimens dynamically loaded during the split Hopkinson (Kolsky) bar tests in a regime close to simple shear conditions was studied. The lateral surface of the specimens was investigated in-situ using a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time allowed one to trace the evolution of plastic strain localization. The process of target perforation involving plug formation and ejection was examined using a high-speed infra-red camera and a VISAR velocity measurement system. The microstructure of tested specimens was analyzed using an optical interferometer-profiler and a scanning electron microscope. The development of plastic shear instability regions has been simulated numerically.

The paper focuses on the experimental and theoretical study of instability of plastic strain and its localization in materials subjected to high-velocity perforation. The online study of the specimen surface was made using the high-speed infrared camera CEDIP Silver 450M. The distribution of the temperature field obtained at different instants of time allows getting insight into the evolution of the process of plastic strain localization. After testing, the structure of the specimen material was examined by scanning electron microscopy. In our investigation, the mechanisms of plastic shear instability and localization of plastic strain (in the three-dimensional statement) have been simulated numerically, and the peculiarities of the kinetics of microshear accumulation in the material have been analyzed.

Experimentally observed universality of fluctuation statistics in fully developed turbulent shear flow is linked to the dynamics of collective shear localization modes and new class of critical phenomenon of solid with defects—structural-scaling transition. Universality appears as self-similarity of the distribution function of momentum power fluctuations on rotating discs (the Karman test) on the four orders of the Reynolds number that corresponds to the sharp power decay injected into the flow. Similar features of the coherent multiscale behavior established under multiscale plastic flow instability in AlMg alloy revealing the Portevin–Le Chatelier effect. Localized shears could be considered as mesoscopic structural defects in liquids appearing due to the collective molecular slips.

The paper focuses on the experimental and theoretical study of plastic deformation instability and localization in materials subjected to dynamic loading and high-velocity perforation. We investigate the behavior of samples dynamically loaded during Hopkinson-Kolsky pressure bar tests in a regime close to simple shear conditions. Experiments were carried out using samples of a special shape and appropriate test rigging, which allowed us to realize a plane strain state. Also, the shear-compression specimens proposed in were investigated. The lateral surface of the samples was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. Use of a transmission electron microscope for studying the surface of samples showed that in the regions of strain localization there are parts taking the shape of bands and honeycomb structure in the deformed layer. The process of target perforation involving plug formation and ejection was investigated using a high-speed infra-red camera. A specially designed ballistic set-up for studying perforation was used to test samples in different impulse loading regimes followed by plastic flow instability and plug ejection. Changes in the velocity of the rear surface at different time of plug ejection were analyzed by Doppler interferometry techniques. The microstructure of tested samples was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The subsequent processing of 3D deformation relief data enabled estimation of the distribution of plastic strain gradients at different time of plug formation and ejection. It has been found that in strain localization areas the subgrains are elongated taking the shape of bands and undergo fragmentation leading to the formation of super-microcrystalline structure, in which the size of grains is ~300nm. Rotational deformation modes give rise to the high angular disorientations of grains. The development of plastic shear instability regions has been simulated numerically. For this purpose, we use a recently developed theory, in which the influence of microshears on the deformation properties of materials has been studied by the methods of statistical physics and thermodynamics of irreversible processes. The results of theoretical and experimental studies suggest that one of the mechanisms of the plastic shear instability and localization of plastic strain at high-velocity perforation is related to structural and kinetic transitions in microshear ensembles.&nbsp

We have studied, both experimentally and theoretically, the mechanisms of plastic shear localization during the dynamic deformation (adiabatic shear band formation) of metals. Instability mechanisms are frequently associated with collective effects in microdefect ensembles in spatially localized regions. Infrared in-situ scanning of instability regions and further investigation of a dislocation substructure confirm that non-equilibrium transitions play a key role in defect ensembles during the evolution of a localized plastic flow. The use of equations reflecting a relationship between non-equilibrium transitions and plastic flow has made it possible to perform simulations for plastic shear localization.

The behavior of specimens dynamically loaded during split Hopkinson (Kolsky) bar tests in a regime close to simple shear conditions was studied. The lateral surface of the specimens was investigated in-situ using a high-speed infrared camera CEDIP Silver 450M. The temperature field distribution obtained at different time allowed one to trace the evolution of plastic strain localization. The process of target perforation involving plug formation and ejection was examined using a high-speed infrared camera and a VISAR velocity measurement system. The microstructure of tested specimens was analyzed using an optical interferometer-profiler and a scanning electron microscope. The development of plastic shear instability regions has been simulated numerically.

The behavior of specimens dynamically loaded during the split Hopkinson (Kolsky) bar tests in a regime close to simple shear conditions was studied. The lateral surface of the specimens was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. The process of target perforation involving plug formation and ejection was examined using a high-speed infra-red camera and a VISAR velocity measurement system. The microstructure of tested specimens was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The development of plastic shear instability regions has been simulated numerically.

Plastic strain localization and fracture of dynamically loaded metallic samples occurred during plug formation are investigated. These processes are closely related to the instability of plastic flow and can be attributed to structural-scaling transitions in mesodefect ensembles. The multiscale nature of defect structure allows one to use the fractal concept for quantitative analysis of both the fracture surface and the inner structure of deformed material. The scaling properties of fracture surfaces are established in terms of the roughness index (Hurst exponent) as the characteristics of strain localization and fracture.

The developed statistical model of solid with mesoscopic defects allowed the formulation of phenomenological model in terms of two independent variables—the defect density tensor and structural scaling parameter and the simulation of shock wave propagation in the linkage with structural relaxation phenomena. It was established the link of the Hugoniot elastic limit with kinetics of structural transition (mathematically related to the defect density tensor) in the structural metastability area, that has generally thermally‐activated character. The development of plastic front is described as the consequence of self‐consistent structural (orientation) transition in microshear ensemble that is realized due to the kinetics of structural scaling parameter. The present investigation was directed to describing of the failure phenomena. Two cases are discussed (quasi‐brittle and elastic‐plastic behavior).