OBRABOTKAMETALLOV Vol. 26 No. 1 2024 TECHNOLOGY where where ε0 is the strain corresponding to the stress σ0; ε is the current value of the strain; m is the coeffi cient of deformation hardening equal to 0.3T ′ (where T ′ is the homological temperature of the processed material). However, equation (1) cannot be used to determine the yield stress for highly dynamic cutting processes (which include high-speed milling), since it does not take into account changes in deformation temperature and strain rate for changes in yield stress. In addition, the deformation temperature and the strain rate have a joint eff ect on the change in the yield stress, and are not free multipliers, as stated in a number of papers [18, 19]. The infl uence of temperature and strain rate in various equations for modeling changes in yield stress is taken into account by introducing appropriate multipliers. In particular, at present, the most popular JohnsonCook plasticity model, which determines the behavior of a material during hardening, takes into account the infl uence of the strain rate on the change in yield stress using the dynamic coeffi cient Kε [17, 20]. However, in the Johnson-Cook equation, the dynamic factor does not depend on temperature changes [21], while experimental data obtained by a number of scientists [16, 22, 23] confi rm the combined eff ect of strain rate and temperature on the dynamic factor (fi gure 1). Fig. 1. Dependence of the Dynamic factor on the Homologous temperature [21, 24] The diagram (fi gure 1) shows empirical results describing the infl uence of such factors as strain rate and homological temperature on the value of the dynamicity coeffi cient, as well as values approximated for the same conditions for the Johnson-Cook plasticity model [21]. In experiments, the strain rate varied by 1,000 and 2,000 times. And the change in homological temperature was achieved due to various processing materials (copper, steel, lead, aluminum). A group of aluminum alloys D16T, AMg6, 2024-T3 was selected for the research because it has similar physical properties and can be used for the manufacture of fuel tanks in the aircraft and rocket industry. The calculations carried out in this research were performed on the basis of the dependences of the change in the actual ultimate strength on temperature during high-temperature tests of aluminum alloys (Table 1) [18, 19]. Based on Table 1, graphs of the change in ultimate strength versus test temperature were plotted (fi gure 2). These graphs were approximated by an exponential curve with an accuracy of 0.9351 for the D16T alloy and 0.9544 for the AMg6M alloy, which gives satisfactory results. Exponential extrapolation was chosen due to the fact that exponential equations are easier to integrate and diff erentiate than, for example, equations with polynomial dependence (although polynomial interpolation is a little more accurate), and linear approximation gives less accurate values for alloy D16T and is 0.8971, and for alloy AMg6M practically does not diff er from exponential and is 0.9318.
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