Use of a vector damage parameter in modeling of long-term strength of metals

We consider the results of known tests of tubular specimens under a constant axial stress and a constant or alternating tangential stress. The cyclic variation in the sign of the tangential stresses significantly increases the time to fracture. The modeling of long-term strength of metals in unsteady complex stress states encounters significant difficulties. The application of the kinetic theory of long-term strength is apparently the most promising method for solving this problem. As a rule, the use of a scalar damage parameter does not permit describing the specific characteristics of fracture for various loading programs. The use of a tensor damage parameter also encounters difficulties because of a large number of functions and material constants contained in the kinetic equations. In this paper, we propose to use a vector damage parameter to describe the experimental data under study.