Selection of complex equivalent stress for two different variants of the plane stress state

To describe the creep rupture process under complex stress, various equivalent stresses are considered. From them, the equivalent stress at which the total error of the difference between the experimental and theoretical values takes the smallest value among the considered equivalent stresses is selected. In this paper, three basic equivalent stresses are considered, as well as two complex equivalent stresses, which are a linear combination of the basic ones with one material parameter. The analysis of the total errors in the considered experimental data shows that, with the simultaneous effect of internal pressure and the axial force on the wall of tubular specimens (or biaxial tension of a plane element), a complex equivalent stress should be used in the form of a combination of the maximum normal stress and the Mises stress. For simultaneous torsion and tension of tubular specimens (or simultaneous tension and compression of a plane element), a complex equivalent stress should be used in the form of a combination of the maximum normal stress and the doubled maximum tangential stress.