ОЦЕНКА РЕСУРСНЫХ ХАРАКТЕРИСТИК ПОЛИКРИСТАЛЛИЧЕСКИХ КОНСТРУКЦИОННЫХ СПЛАВОВ ПРИ ДЕГРАДАЦИИ ПО СОВМЕСТНЫМ МЕХАНИЗМАМ УСТАЛОСТИ И ПОЛЗУЧЕСТИ МАТЕРИАЛА

Abstract

The problem of assessing the resource characteristics of responsible engineering facilities, taking into account the peculiarities of operational loading conditions, is discussed. The processes of degradation of the initial strength properties of structural materials (metals and their alloys) under combined fatigue and long-term strength mechanisms are considered. A mathematical model describing the processes of cyclic viscoplastic deformation and accumulation of fatigue damage in structural alloys under multiaxial disproportionate modes of combined thermomechanical loading has been developed from the modern positions of mechanics of the damaged medium and fracture mechanics. The model consists of three interrelated components: relations determining the cyclic viscoplastic behavior of the material, taking into account the dependence on the destruction process; evolutionary equations describing the kinetics of the damage accumulation process; criteria for the strength of the damaged material. The variant of the cyclic determining relations is based on the idea of the existence of plasticity and creep surfaces in the stress space and the principle of gradiency of the velocity vectors of plastic deformations and creep deformations to the corresponding surface at the loading point. These equations of state reflect the main effects of the process of cyclic viscoplastic deformation of the material for arbitrary complex loading trajectories. The variant of kinetic equations of damage accumulation is based on introduction of a scalar damage parameter and on energy principles. Ittakes into account the main effects of formation, growth and fusion of microdefects under arbitrary complex modes of combined thermomechanical loading. A joint form of the evolutionary equation of damage accumulation in the areas of low-cycle fatigue and long term strength is proposed. As a criterion of the strength of the damaged material, the condition of reaching the critical value of the damage value is used. The results of numerical modeling of deformation processes and damage accumulation in structural alloys with degradation mechanisms combining fatigue and long-term strength of the material are presented. The results of the comparison of calculated and experimental data showed that the proposed model of the mechanics of the damaged medium qualitatively and with the accuracy necessary for practical calculations quantitatively describes the processes of destruction of hazardous areas of structural elements under the combined actions of degradation mechanisms of fatigue and long-term strength.