EVALUATION OF HYDROSTATIC PRESSURE IN EQUAL CHANNEL ANGULAR PRESSING CONSIDERING CHANNEL GEOMETRY AND FRICTION MODEL

Abstract

The relevance of this work stems from the substantial potential of Equal-Channel Angular Pressing (ECAP) for producing unique material structures, which necessitates a comprehensive understanding of the influence of all process parameters. Hydrostatic pressure is a key factor governing microstructure evolution during severe plastic deformation; however, its dependence on tool geometry and friction conditions has not been fully elucidated. This study is dedicated to the quantitative assessment of the effect of the channel intersection angle and the contact friction coefficient on the magnitude of hydrostatic pressure within the deformation zone during ECAP. Using the finite element method (FEM) within the DEFORM-2D software package, the process was simulated for an ideal plastic material. The investigation covered channel intersection angles within the range effective for nanostructure formation, specifically from 90° to 120°, and Amontons-Coulomb friction coefficients ranging from 0.05 to 0.3. To verify the accuracy of the results, the obtained numerical data were compared with the known analytical solution by Segal. It was established that an decrease in the channel angle leads to a reduction in hydrostatic pressure by 34–51%, whereas an increase in friction elevates it by 31–48%. Significant discrepancies between the FEM data and the analytical model were identified in regions of low friction combined with large angles, and high friction combined with small angles. It is demonstrated that these discrepancies are attributable to the formation of a corner gap or a fan zone within the deformation zone, phenomena not accounted for in the classical analytical approach. Based on regression analysis, an interpolation formula for calculating hydrostatic pressure was derived. Critical values of the friction coefficients delineating different metal flow modes were determined, and the relationship between the Amontons-Coulomb and Siebel friction models in the context of ECAP was established. The results enable improved accuracy in predicting the stress state of billets and facilitate the optimization of pressing parameters for obtaining materials with targeted properties.