The Johnson–Cook constitutive equation is very widely used for simulating cutting processes. Different methods are applied for establishing parameters of the constitutive equation. Based on the methods analysed in this study, two algorithms were worked out to determine the constitutive parameters for the prevailing conditions during cutting processes. In the first algorithm, all constitutive parameters were established simultaneously with standardized test methods. In the second algorithm, the constitutive parameters were established separately in accordance with the cutting conditions prevailing in machining processes. The developed methodology was verified with AISI 1045 heat-treatable steel and Ti10V2Fe3Al (Ti-1023) titanium alloy. The two materials were examined in standardized tensile and compression tests with varying strain rates and temperatures. In addition, the kinetic characteristics of the orthogonal cutting process were established. Based on the results obtained by experiment and the algorithms developed, the constitutive parameters for the cutting conditions were calculated. The parameters were used to determine the material model for simulating the orthogonal cutting process. The algorithms developed were verified by comparing the simulated and experimentally determined kinetic cutting characteristics, which confirmed their good quality.

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This paper analyses experimental results and different hypotheses about the resistance of the machined material to plastic deformation in machining. It is necessary to take into account that strain rate and temperature affects the mechanical properties of the material. It is useful to describe the regularities of material resistance to plastic deformation with differential equations, determining a dependence of the specific deformation work on deformation. For machining processes, the correlations between yield point and deformation or rather flow curves are analytically deduced from the differentiation of the specific deformation work. It has been found out that the flow curves are vaulted for the adiabatic conditions of deformation in the chip forming area and the accumulation zones near the cutting edge. The yield point here reaches its maximum for deformations that are usually lower than the true final shear of the material penetrating through the chip forming area. It is suggested to take these maximum values of the yield point as mechanical properties of the material to be machined. The main goal of the theoretical and experimental investigations presented in this paper is to establish the analytical dependence of the specific deformation work and therefore also of yield point and specific tangential forces on deformation, taking account of the effect of temperature on yield point. The main advantages of applying the specific deformation work is not only its direct relation to deformation temperature but also the possibility of experimentally determining this work through specific tangential forces and true final shear. In this way it is possible to establish how deformation temperature affects yield point by means of empirical constants.

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