МОДЕЛИРОВАНИЕ УСТАЛОСТНОЙ ДОЛГОВЕЧНОСТИ КОНСТРУКЦИОННЫХ СПЛАВОВ ПРИ ДВУХЧАСТОТНОМ НАГРУЖЕНИИ

Abstract

The processes of fatigue life of polycrystalline structural alloys under the combined action of low- and high-cycle fatigue mechanisms are considered. From the standpoint of damaged medium mechanics (DMM), a mathematical model has been developed that describes the processes of plastic deformation and the accumulation of fatigue damage. The DMM model consists of three interrelated parts: relations that determine the cyclic elastoplastic behavior of the material, taking into account the dependence on the fracture process; equations describing the kinetics of fatigue damage accumulation; criterion for the strength of the damaged material. Variant of the constitutive relations for elastoplasticity is based on the concept of a microplastic loading surface in the von Mises form and the principle of the gradient of the plastic strain rate vector to the surface at the loading point. This version of the equations of state reflects the main effects of the process of cyclic plastic deformation of the material for arbitrary complex loading trajectories. A variant of the kinetic equations for the accumulation of fatigue damage is based on the introduction of a scalar damage parameter, is based on energy principles and takes into account the main effects of the formation, growth and fusion of microdefects under arbitrary complex loading conditions. A unified form of the evolutionary equation for the accumulation of fatigue damages for low-cycle and high-cycle fatigue is proposed. As a criterion for the strength of the damaged material, the condition for reaching the critical value of the damage is used. To assess the reliability and determine the limits of applicability of the constitutive relations of the DMM, numerical studies of the processes of accumulation of fatigue damage by cyclic inelastic deformation and fatigue failure of steel 20 and 08Х18Н12Т were carried out under single-frequency loading of the upper frequency and two-frequency loading with different amplitude ratios. And the comparison of the obtained numerical results with the data of field experiments is carried out. The results of comparing the calculated and experimental data showed that the developed model of the damaged environment reliably describes the durability of structures under the action of low- and high-cycle fatigue mechanisms.