Different Options of Accounting for Loosening in the Theory of Isotropic Plasticity

Two types of constitutive equations accounting for the stress mode and the loosening of the material during elastoplastic deformation are considered. The constitutive equations of one type include two nonlinear relationships between the first invariants of the stress and strain tensors and between the second invariants of the deviator tensors and include the third invariant of the stress deviator. The constitutive equations of the other type use equivalence stress containing the first and second invariants of the stress tensor. Literature experimental data for tubular isotropic specimens under tension, compression, torsion, and internal pressure are used for assessing the loosening of the material.