The kinetics of damage accumulation in heat-resistant steels under different loading conditions

Abstract

620.178.15/179.119 and T. N. Mozharovskaya The investigation results are presented for the kinetics of damage accumulation and the process of deformation in a heat-resistant steel 10GN2MFA for different loading conditions under complex stress state.Introduction. At present, investigations on the assessment of the load-carrying capacity and life of structures performed with consideration for the current state of structural materials are based on a rather large volume of theoretical developments whose foundation is formed by hypothetical prerequisites concerning the properties of materials with no consideration for their current state and actual operating conditions. The development of the methods for assessing the residual life of machines and structures, the majority of which operates under cyclic loading, is the urgent problem. The main reason for the premature loss of the load-carrying capacity for that kind of objects is the out-of-control damage accumulation and crack formation processes in structural materials.Testing Procedure. In this paper, the results of experimental investigations are presented for the development of the process of deformation and kinetics of damage accumulation in heat-resistant steel 10GN2NMFA at room temperature under conditions of a single load application, stepwise cyclic and continuous cyclic loadings at complex stress state. The tests were performed on thin-walled tubular specimens (D out d = 50, where D out is the outer diameter of the specimen and d is the specimen wall thickness) loaded by the axial force and internal pressure in different combinations using a test rig type SNT-8U [1]. The experiments involved a uniaxial (K

Studies on damage accumulation kinetics in a metal under cyclic loading in the multiaxial stress state

“…As was shown earlier [8], homogeneity factor reduction rates with an increase in the maximum stress intensities under uniaxial cyclic loading are somewhat higher than those under nonuniform biaxial one. The results of experimental investigations substantiate this tendency.…”

“…The above is substantiated by the data (Figs. 2 and 3) similar to these for nonuniform biaxial loading [8], where N is the number of loading cycles at each step preceding full specimen unloading and shifting to the next loading step of a higher stress level, without specimen fracture, N b is the number of loading cycles to specimen fracture, s i , ¢ s i max , and s i max are the maximum stress intensities at an examined loading step with loading termination without specimen fracture, and after equilibrium attainment of the specimen's metal, respectively, and s ib is the stress intensity corresponding to specimen fracture under single loading. Homogeneity Factor Variations with a Stress State.…”