Elastic-plastic behavior and fracture of structures with loss concentrators under cyclic loads

The results of experimental and theoretical studies of structures with stress concentrators under cyclic loading are presented. The studies were carried out on cylindrical specimens with an annular undercut under mild cyclic loading. The sample material is bronze alloy BrKh08-Sh. When testing samples using the digital image correlation method, the deformation of the material on the surface of the undercut is measured, which makes it possible to determine the nature of the change in its range from cycle to cycle. For mathematical modeling of elastoplastic behavior and failure 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 monotonic and cyclic loading. This division allows one 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 fitting and stepping out of the elastoplastic hysteresis loop. The plasticity model makes it possible to assess the damaged state of the material based on the kinetic equation of damage accumulation based on the energy principle (the work of microstresses on the field of plastic deformations). The material behavior model is embedded in the finite element software package. Based on the calculation results, cartograms of the accumulated plastic deformation and stress intensity were constructed. Comparison of the results of calculations and experiments on the range of axial deformation, average axial deformation on the surface of the undercut and the cycle of cycles to failure is carried out. It was found that in a structure with a groove with a radius of 0.25 mm in the concentration zone, rigid loading is realized, and with a radius of 1 mm in the concentration zone, soft asymmetric loading with one-sided accumulation of deformation (stepping out) is realized. There is a decrease in durability with a decrease in stress concentration due to the different nature of the change in the stress-strain state.