Global Journal of Science Frontier Research, A: Physics and Space Science, Volume 23 Issue 11

idea of the dependence of the critical parameters of the localization onset on the initial structures. The majority of works on studying LSBs relates to the materials engineering aspect, which accounts for availability of good measuring equipment. The microstructure characterization after dynamic loading is very important for understanding the shear localization mechanism. In spite of a high level of description of changes in the substance that take place after its impulse loading, the factors causing them remain unknown , since the samples retained after explosive loading are studied. The ratio between changes in the sample structure during deformation and after it can be ambiguous. According to authors' opinion [3], the physical interpretation of these phenomena often turns out to be far from reality. One of the reasons for this state is the failure to take into account the compressibility of a solid under impulse loading. The strain localization process accompanies almost all shock and explosive impacts on the material. Pulse processes differ markedly from quasi-static ones, since they lead to a change in the structure and density of the metal, the propagation of compression waves (shock waves) or unloading waves, and the formation of a mass flow of matter, which cannot be ignored. The review on the problem of strain localization in metals is presented and the mechanism of the formation of localized strain bands (LSBs) and mechanisms accompanying the localization of processes leading to changes in the band microstructure are studied in this article. The LSBs are considered as material prefracture. The wave pattern of the process was considered nearly for every experiment and eliminated an ambiguity in the interpretation of experimental data based on the study of the samples retained after explosive loading. The basis of this work is taking into account the compressibility of the material. a) Why “localized strain bands” rather than “adiabatic shear bands”? Under competitive conditions, the operation of Damageability of Metals under Impulse Loading © 2023 Global Journals 1 Year 2023 22 Frontier Research Volume XXIII Issue ersion I VXI ( A ) Science Global Journal of Adiabatic shear bands as a consequence of thermal decompression of the material must have a high temperature. It seems impossible nowadays to experimentally measure the temperature in localization bands and, hence, it is calculated. According to different sources, the calculated temperature is 500ºC [4], 600ºC [5], or 800ºC [6]. The Jones-Cook [6] and Zerilli- Armstrong [7] models most commonly used in temperature calculations contain five fitting parameters. Such models are not suitable for describing impulse processes [8], because they inadequately describe the processes behind the shock wave front and ignore the wave amplitude, density, flow limit change, and plastic properties of materials. Doubts about thermal softening were given [9]. The temperature recorded by an infrared detector is total over the surface area (spot radius ~ 45 µm) and is not characteristic of the band temperature. As shown in [9], an increase in the total temperature the internal heating source noticeably reduced the rate of heat removal from LSBs. The titanium alloy had the highest temperature heating compared to other metals. Thus, the maximum temperature of a localization strip with a thickness of 50 μ m from the initial temperature, which is close to the residual temperature, is 220°C, while for an aluminum alloy it is only 65°C, the cooling time of a LSB with a thickness of 10 μ s under the competitive conditions between thermal conductivity and the operation of an internal heating source does not exceed 1 µs. The name of localized strain bands as adiabatic appears outdated and does not reflect their specific features. before localization is quite insignificant. Taking into account thermal conductivity of the medium adjacent to the hot spot shows that the lifetime of the spot with an initial temperature of 800°C is only 1 ns [10]. The work [5] is interesting because the model of a deformed body is not used to calculate the temperature. The irreversible loss of plastic deformation energy under impulse loading is estimated on the account of the geometric interpretation of the conservation laws. In the P-V diagram (pressure-specific volume), the irreversible energy is equal to the surface area between the Rayleigh-Michelson straight line and the Hugoniot curve. The authors suggest that the loss of plastic flow stability and the transition from uniform deformation to that when a “trap” is formed to capture the released energy occur at a certain shock wave pressure. The authors of [5] attributed all the released heat to a thin shear band when obtaining the temperature in the band equal to 600 0 C, which is 250 0 С higher than the shock compression temperature. According to the estimates [5], the calculated time of high temperature existence is several nanoseconds after the passage of the shock wave front. It seems doubtful that such a short heating duration could significantly influence the formation of the macrolocalization process. The solution of the nonstationary one- dimensional nonuniform partial differential heat equation is given in [11]. The shock wave at pressures of 10–20 GPa is weak, the temperature at the wave front, as a rule, does not exceed 350°C, and the residual heating is 30°C. Instant heating at the shock wave front was specified to be 350º С . Localized shear bands were simulated by thin metal plates, on the surfaces of which a residual temperature of 30ºC was specified. During high-speed deformation, the heat removal of energy was carried out by thermal conductivity. The internal heating source due to plastic deformation was simulated by the equation: ( , ) = 600 exp (− ) � º � .