Modeling the Long-Term Strength of Metals in an Unsteady Complex Stress State

The known results of tests for long-term strength in an unsteady complex stress state are simulated using the kinetic theory. Experimental data are usually described using a vector damage parameter with a piecewise-constant damage accumulation rate. The long-term strength of tubular samples is simulated under the simultaneous action of a constant axial stress and a shear stress once or periodically changing sign. To describe the known effect in which the time to fracture in a uniaxial plane stress state is several times smaller than the time to fracture under a uniaxial tension, a variant of Yu.N. Rabotnov’s kinetic theory with additional consideration of the anisotropy of the material is proposed. The long-term strength with an abrupt change in the stress intensity is simulated by two methods: with allowance for the damage accumulation only in the creep process and with allowance for the additional damage accumulation under instant loading. All the variants of the kinetic equations proposed lead to a good agreement between the experimental and theoretical values of the time to fracture.