Damage of structural materials under complex low-cycle loading

On the basis of the concepts of the continuum mechanics of damage, we propose an engineering method for the analysis of the kinetics of accumulation of scattered defects in metallic structural materials under conditions of elastoplastic deformation and low-cycle fatigue. It is shown that, in the general case of complex loading for the complex stress state, it is reasonable to use the specific energy of additional stresses (with regard for the arc of plastic strains in a loading cycle) as a parameter of damage for two types of fracture (rupture and shear). __________ Translated from Problemy Prochnosti, No. 6, pp. 25–34, November–December, 2007.     

Evaluation of the strength of structural materials with cracks under complex loading

We develop an experimental procedure and geometry of the specimens for the evaluation of the characteristics of crack growth resistance of structural materials for various macromechanisms of fracture (modes I, II, and III). We plotted diagrams of the limiting-equilibrium state of a body containing a crack (its strength) under complex proportionally increasing loading.     

Deformation resistance and limiting state of structural materials in multiaxial low-cycle deformation

The results are presented of investigations into the relationships governing low-cycle fatigue of VT14 alloy and 14Kh17N2 steel at T=290 K under the conditions of proportional and nonproportional rigid low-cycle loading. Symmetric and pulsed (nonzero) deformation cycles were examined. The limits of applicability of the determining equation in the form of a generalized diagram of low-cycle loading for the case of piecewise-broken flat trajectories were determined. The results show that strain asymmetry has a strong effect on the endurance (in the stage of macrocrack formation) because of the special features of the deformation resistance of structural materials in the presence of a mean strain and the effect of the properties of cyclic hardening and softening.Translated from Problemy Prochnosti, No. 10, pp. 11–16, October, 1990.     

A method for low-cycle fatigue life assessment of metallic materials under multiaxial loading

A new method of fatigue life assessment under multiaxial low-cycle regular and irregular loading is proposed, which is based on the modified Pisarenko-Lebedev criterion, the linear damage accumulation hypothesis, and the nonlinear Manson approach. The results of low-cycle fatigue tests of titanium alloy VT9 under irregular proportional and non-proportional biaxial loading are given. The tests were carried out at three Mises strain levels (0.6, 0.8, and 1.0%) with various combinations of proportional and non-proportional strain paths. All the tests were carried out at room temperature. The proposed method turned out to be effective and to allow for such factors as strain state type, strain path type and loading irregularity. __________ Translated from Problemy Prochnosti, No. 1, pp. 56–59, January–February, 2008.     

Models of endurance under low-cycle loading

Moscow. Translated from Problemy Prochnosti, No. 4, pp. 8–13, April, 1989.     

Procedure for the evaluation of the accumulation of defects in metallic structural materials under complex elastoplastic loading

Within framework of the continual fracture mechanics, we describe the engineering approach to the assessment of scattered microdamage accumulation kinetics in metallic materials under elastoplastic loading conditions in case of plane stressed state. Automatized experimental stand and the respective investigation technique are discussed. The stand has been developed based on modification of the UMé-10T electromechanic test machine. State-of-the-art computer technologies and microprocessing hardware are incorporated in the stand automation. We present the technique of experimental assessment of damage accumulation kinetics in metallic structural materials under complex elastoplastic loading conditions with account of two different fracture (cleavage and shear) processes, which technique is based on measuring the specific electric resistance of the specimen. __________ Translated from Problemy Prochnosti, No. 1, pp. 128–137, January–February, 2006.     

Effect of structural parameters on the fatigue failure of cast steels in loading with low-cycle overloads

Experiments were carried out to examine the effect of structural parameters on the fatigue resistance in block loading with elastoplastic (low-cycle) overloads. Differences in the structural parameters were produced by heat treating 20GL steel by different techniques: normalizing, quenching and tempering, thermocyclic treatment (TCT), and by alloying. The results are presented of fractographic and metallographic analysis of specimens subjected to different heat treatments and fractured as a result of fatigue tests. An equation is derived for predicting the fatigue endurance of a specimen in block loading in relation to the mechanical characteristics and structural parameters of the steel.Translated from Problemy Prochnosti, No. 7, pp. 51–57, July, 1991.     

Strength in low-cycle loading of high-nickel alloy being irradiated

The results are given of an investigation of low-cycle fatigue of the austenite class 03Kh20N45M4BCh chromium alloy, realized in its application to the selection of materials for the manufacture of structural elements of the thermonuclear reactor discharge chamber. The loading regime consists of alternating elastoplastic strain by twisting a thin-walled tubular specimen with holdings of 200-sec duration. Radiation tests were carried out in a materials science channel of the WR-M (water-cooled and water-moderated) reactor of the Institute of Nuclear Research at the Academy of Sciences of the Ukrainian SSR in a flux of fast neutrons 4.5 ' 10¹³ neutron · cm² · sec. The effect of neutron irradiation on strain and strength properties of the investigated alloy are evaluated. Comparison is made of the data on the effect of irradiation on the low-cycle fatigue of some steels.Translated from Problemy Prochnosti, No. 2, pp. 46–50, February, 1990.     

Material characterization of SS 316 in low-cycle fatigue loading

This study deals with simulation of low-cycle fatigue (LCF), followed by evaluation of fatigue parameters, which would be suitable for estimating fatigue lives under uniaxial loading. The cyclic elastic–plastic stress–strain responses were analyzed using the incremental plasticity procedures. Finite-element (FE) simulation in elastic–plastic regime was carried out in FE package ABAQUS. Emphasis has been laid on calibration of SS 316 stainless steel for LCF behavior. For experimental verifications, a series of low-cycle fatigue tests were conducted using smooth, cylindrical specimens under strain-controlled, fully reversed condition in INSTRON UTM (Universal Testing Machine) with 8,800 controller at room temperature. The comparisons between numerical simulations and experimental observations reveal the matching to be satisfactory in engineering sense. Based on the cyclic elastic–plastic stress–strain response, both from experiments and simulation, loop areas, computed for various strain amplitude, have been identified as fatigue damage parameter. Fatigue strain life curves are generated for fatigue life prediction using Coffin–Manson relation, Smith–Watson–Topper model, and plastic energy dissipated per cycle (loop area). Life prediction for LCF has been found out to be almost identical for all these three criteria and correlations between predicted and experimental results are shown. It is concluded that the improvement of fatigue life prediction depends not only on the fatigue damage models, but also on the accurate evaluations of the cyclic elastic–plastic stress/strain responses.