Influence of Single and Summary Deformation for the Change of Limit Stress in the Drawing Process Based on the Pelczynski Diagram

摘要

Limit stress diagram by Pelczynski was constructed in the coordinates σ_m - σ_h σ_m — average stress for the process, σ_h — stress according to the Huber hypothesis) based on the hypothesis Huber - de Saint Venant and is consistent connection between the two hypotheses. This diagram allows for presentation the dangerous states of stresses for arbitrary stress state so plane and space (biaxial and triaxial). It also allows for the analysis of stress states occurring in various processes of plastic forming. To determine the state stresses occurring in the technological process starts from the components of the plastic deformation. In the case of a wire drawing process with a circular section in the inlet area of the die there is equality of deformation _2 = _3 and the equality of stress σ_2 = σ_3 (which is uniform biaxial compression), while in a outlet of the die there is a uniaxial tensile σ_1, which cannot achieve a value equal to σ_p (yield strength), since in this case the wire could be deformed outside the die. The aim of this study was to construct the Pelczynski diagram in such a way to show on the example of brass wire M63, the course of the stresses in the drawing process. The research program included: - realization of the drawing processes in order to obtain samples of varying degrees strengthening, - determination on the basis of tensile strength the properties R_m, R_(p0.2) and cohesive strength of R_0 for varying degrees of strengthening, - determine the influence of cold deformation for the course of curve of the yield strength, - constructing a diagram of drawing process on a background of the diagram of yield strength in this process.