About drawing of the yield surface for steel 45 and verification of the postulate of isotropy on straight-line paths during repeatedsign-variable loadings

In article are presented results of experimental studies at repeated sign-variable loadings of a thin-walled tubular specimen at stretching compression and torsion. The experiments were implemented on an automated computational and experimental installation for complex loading SN-EVM named A.A. Ilyushin in the vector space of deformation (rigid loading). According to experimental data evaluated the Baushinger effect and magnitude of secondary yield strength at various admissions on residual defor- mation. Given the influence of the admission on residual deformation on radius function and position of the center of spherical yield surface in stress space, used in the plastic-flow theory. With increase in the admission at residual deformation the parameter characterizing Bauschinger effect and the radius func- tion of the yield surface increases, and the displacement of its center decreases. With increasing length of the arc of plastic deformation parameter characterizing the Bauschinger effect decreases and tends to a stationary value. It is established that the radius of spherical yield surface makes temporary de- crease and then increase with increasing length of the arc of the plastic deformation. Some mathemati- cal models of the plastic-flow theory attributed this decrease in the radius of the yield surface not with change of internal structure of a material at meso-level and orientation of microtension, and with an elastic softening initially isotropic body, mistakenly believing in this strain rate negative. For the realized types of experimental path of repeated sign-variable loadings with breaks on 180 degrees verification of the postulate of isotropy by A.A. Ilyushin showed that on scalar and vector properties it is carried very well.