Computational and Experimental Analysis of Resistance to Low-Cycle Deformation of Heat-Resistant Alloy

Abstract

It is noted that, in the general case, diagrams of cyclic elastoplastic deformation of a material characterize its resistance to low-cycle loading and display the relationship between current stress values and deformation during deformation. Such diagrams in the mechanics of deformation and fracture are described by complex equations of state that depend nonlinearly on the conditions and loading modes, including temperatures, strain rates, cycle shapes, types of stress state, absolute dimensions of sections, types of working media, types of structural material, etc. The mentioned factors in their entire complex influence the shape of curves (diagrams) of material deformation and the main parameters of the equations of state describing them, for example, such basic characteristics of mechanical properties as the modulus of elasticity, yield stress and ultimate strength, and indicators of static and cyclic hardening. As exemplified by experimentally obtained data on the kinetics of cyclic and one-sided accumulated plastic deformations in each of the half-cycles (cycles) of loading during static and low-cycle tests of specimens from a heat-resistant nickel alloy, it is shown that, under conditions of cyclic elastoplastic deformation, these deformation characteristics have an essentially nonlinear pattern of change, which is described on the basis of power equations and the parameters of cyclic deformation diagrams included in them. Here, the parameters of these equations depend on the type of cyclically hardening, softening, or stable material during its deformation in the elastoplastic region. It is noted that the resistance to cyclic elastoplastic deformations of a material can be described by a set of analytical expressions with a kinetic function included in them, which varies over the number of loading half cycles, in the form of power or exponential expressions depending on the cyclic properties of the material and data on the characteristics of the mechanical properties of specific structural materials. The obtained computational and experimental data on the kinetics of deformations of the alloy under study during its cyclic elastoplastic loading and on the parameters of the deformation diagrams, which are the basic characteristics for the corresponding equations of state, make it possible to fully apply the deformation-kinetic criterion for the accumulation of damage under the considered loading conditions for calculating the durability of structural elements made from it, which are operated, as a rule, under complex temperature and power conditions. The results of the performed experiments and calculations are presented in the form of diagrams of the cycle-by-cycle kinetics of cyclic and accumulated plastic deformations of the studied material under soft and hard loading conditions and in a wide range of test temperatures.