LOW-CYCLE FATIGUE OF STRUCTURES WITH STRESS CONCENTRATORS

Abstract

The results of experimental and theoretical studies of structures with stress concentrators under cyclic loads are presented. The studies were carried out on cylindrical samples with a V-shaped annular recess under mild cyclic loading. The tests were carried out on samples of the BrH08-Sh alloy with a cyclic change in the tensile load from 0 to 10.8 kN. Under such loading, the material in the recess area undergoes cyclic elastoplastic deformation, which leads to destruction as a result of low-cycle fatigue. For mathematical modeling of the elastic-plastic behavior and destruction of structures with stress concentrators, a variant of the theory of plasticity based on the theory of flow under combined hardening is used. In the chosen plasticity model, a memory surface is introduced that separates the processes of monotonous and cyclic loading. This separation makes it possible to take into account various features of isotropic and anisotropic hardening of the material. Anisotropic hardening is represented as a sum of microstresses of three different types, which make it possible to describe the effects of landing and stepping of the elastic-plastic hysteresis loop. The plasticity model makes it possible to assess the damaged state of a material based on the kinetic equation of damage accumulation based on the energy principle (the operation of microstresses in the field of plastic deformations). The material behavior model is embedded in the finite element software package SIMULIA Abaqus. The results of calculations and experiments on the magnitude of axial deformation, the average axial deformation on the surface of the recess and the number of cycles to failure are compared. It is found that in a design with a recess with a radius of 1 mm, a soft asymmetric loading with a unilateral accumulation of deformation (ratcheting) is realized in the concentration zone.