OBRABOTKAMETALLOV technology Vol. 25 No. 2 2023 Calculations were performed for the following source data: ϑb = 0.4; L1/D = 4, L2/D = 2; k1 = k2 = 0.2; χ = 0.8; π/16 ≤ α ≤ π/2. The values of density ρ and porosity ϑ of a plastically compressible blank at varying specific pressures 1 p on the working plunger were determined using formulas (4), and (6). As a result, the dependence of pressing pressure 1 α ( ) p and blank porosity ϑ(α) on the angle α (fig. 7) was determined. a b Fig. 7. The dependence of the pressing pressure 1( ) á p (a) and porosity of the workpiece ϑ( ) á (b) on the angle a Numerical simulation of the ECAP process requires the use of a porous material plastic flow model included in modern CAD software. The simulation results significantly depend on the choice of both the material model itself and the methods of its identification. The Gurson model of plasticity of porous metal was used in this paper to describe the rheological behavior of the porous material [33]. The peculiarity of this model, implemented in the Simulia/Abaqus FEA software package, is the ability to describe the processes of both compaction and decompaction of powder materials in a wide range of stress-strain state changes. In this case, such a formulation of the problemmakes it possible to identify areas of the deformable porous blank with a high level of tensile stresses during ECAP, and, therefore, potentially dangerous for the formation of surface cracks and material fracture. The following shows the application of the methodology for identifying porous titanium sponge blank plastic flow model. Simulation modeling of the ECAP process was performed by the finite element method. The problem was solved in the volumetric formulation, but half of the section was used due to symmetry. For modeling, the Explicit CAE calculation module of the Abaqus system was used. A model of porous metal plasticity based on Gurson’s theory of porous metal plasticity was used. The initial relative density was 0.6. The tool was set as absolutely rigid. The contact interaction between the blank and the tool was described by the Amanton-Coulomb friction condition, friction coefficient µ = 0.1. It is assumed that the tangential stresses at the contact surface of the blank and tool are limited to τs = 30 MPa. Simulation using the finite element method makes it possible to estimate many parameters. In this case, it was limited to analyzing of the distribution of stress intensity σi and relative porosity ϑ, which is shown in figs. 8 and 9. Fig. 8 shows the stress intensity distribution in the thin layer located in the vicinity of the section separating the inlet I and outlet II parts of the mold channel. It can be seen that the highest level of stress occurs during equal-channel angle pressing at α = 45°. The ratio of maximum stress intensity values between ECAP schemes with angles of 45 and 60° is 1.57. The distribution of relative density across the section is most uniform when the angle α is 45° (fig. 9, a). At α = 50° porosity is detected only at the end of the blank, even though there is a counter-pressure. In other cases, there is decompaction in the contact zone of the blank with the surface of the mold channel.
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