A Damaged Medium Model for Assessing Life Characteristics of Polycrystalline Structural Alloys with Joint Mechanical Fatigue and Long-Term Strength of Material

Abstract

The processes of initial strength degradation properties of structural materials (metals and their alloys) under combined low-cycle fatigue and long-term strength of material are considered. A mathematical model describing the processes of cyclic viscoplastic deformation and damage accumulation in structural alloys under multiaxial disproportionate modes of combined thermomechanical loading has been developed from the standpoint of mechanics of damaged medium (MDM). The version of constitutive relations of viscoplasticity based on the idea of plasticity surfaces and creep and gradientality of velocity vectors of plastic and creep deformations to the relevant surface in the loading point. This version of state equation reflects the main effects of cyclic viscoplastic deformation of material for arbitrary folded loading paths. The version of kinetic equations for damage accumulation is based on introduction of a scalar damage parameter, on energy principles and takes into account the main effects of nucleation, growth and merging of microdefects under arbitrary complex modes of cyclic thermomechanical loading. The condition when damage degree reaches its critical value is used as a strength damage criterion. The results of numerical simulation of the processes of deformation and damage accumulation in structural alloys under combined fatigue and creep are presented. The results of comparison of calculated and experimental data showed that the proposed MDM model qualitatively and accurately enough for practical calculations quantitatively describes the durability of materials and structures under combined low-cycle fatigue and long-term strength.