I. A. Volkov

Modeling of processes of complex plastic deformation of materials along arbitrary temperature and force loading paths

We develop a mathematical model describing the processes of complex plastic deformation of structural materials (metals and their alloys) under multiaxial nonproportional paths of complex temperature and force loading. To obtain qualitative and quantitative assessment of the constitutive relations developed here, we study how the strain path shape affects the plastic behavior of metals. We show that the version of constitutive relations developed here correctly represents the main elastoplastic deformation effects in metals for arbitrary strain paths.

Numerical Investigation of the Effect of Loading Multiaxiality and Deformation Process Parameters on the Fatigue Life of Metals

Known experimental data on the effect of loading multiaxiality and the type of deformation path on the fatigue damage accumulation process have been analyzed. In terms of the mechanics of a damaged medium, a variant of the defining relations has been developed that describes the processes of elastoplastic deformation and damage accumulation in structural materials (metals and their alloys) in the case of multiaxial nonproportional low-cycle loading paths. The damaged-medium model consists of three interrelated components: relations defining elastoplastic behavior of the material with allowance for the influence of the fracture process, equations describing the damage accumulation kinetics, and a strength criterion for damaged material. To qualitatively assess the defining relations, a numerical experiment to construct equal-damage surfaces has been carried out. The calculated data are compared with the experimental ones. The effect of the stress-state multiaxiality and the type of the deformation path on the low-cycle fatigue life of metals has been investigated. It has been shown that the developed variant of defining relations for a damaged medium reflects correctly the main effects of cyclic elastoplastic deformation and damage accumulation at a multiaxial stress-state and arbitrary material deformation paths.

State Equations of Unsteady Creep under Complex Loading

A mathematical model describing the unsteady creep of metals under complex loading is proposed. The results of numerical simulation of creep of St.304 steel in complex regimes of block multiaxial cyclic deformation are given. The numerical calculation results obtained are compared with the data of full-scale experiments. Creep is simulated in complex deformation processes accompanied by the rotation of main regions of stress, strain, and creep strain tensors.

Assessment of the service life of structural steels by using degradation models with allowance for fatigue and creep of the material

A mathematical model is developed within the framework of equations of damaged medium mechanics to describe the processes of viscoplastic straining and damage accumulation in structural steels with allowance for fatigue and creep of the material. A model of damage summation due to interaction of low-cycle fatigue and creep of the material is proposed. Material parameters and scalar functions of equations of mechanics of damaged media are determined. Viscoplastic straining and fatigue-induced damage accumulation in 08Kh18N10T and 12Kh18N9 are studied numerically, and the data obtained are compared with available results of physical experiments.

Modeling of fatigue life of materials and structures under low-cycle loading

A damaged medium model (DMM) consisting of three interconnected components (relations determining the cyclic elastoplastic behavior of the material, kinetic damage accumulation equations, and the strength criterion for the damaged material) was developed to estimate the stress strain state and the fatigue life of important engineering objects. The fatigue life of a strip with a cut under cyclic loading was estimated to obtain qualitative and quantitative estimates of the DMM constitutive relations under low-cycle loading. It was shown that the considered version of the constitutive relations reliably describes the main effects of elastoplastic deformation and the fatigue life processes of materials and structures.